Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MASS SPECTROMETER
The present invention relates to a mass spectrometer and
a method of mass spectrometry.
It is a common requirement in a mass spectrometer for
ions to be transferred through a region maintained at an
intermediate pressure i.e. at a pressure wherein collisions
between ions and gas molecules are likely to occur as ions
transit through an ion guide. Ions may need to be
transported, for example, from an ionisation region which is
maintained at a relatively high pressure to a mass analyser
which is maintained at a relatively low pressure. It is
known to use a radio frequency (RF) transport ion guide
operating at an intermediate pressure of around 10-3-101 mbar
to transport ions through a region maintained at an
inteimediate pressure. It is also well known that the time
averaged force on a charged particle or ion due to an AC
inhomogeneous electric field is such as to accelerate the
charged particle or ion to a region where the electric field
is weaker. A minimum in the electric field is commonly
referred to as a pseudo-potential well or valley. RF ion
guides are designed to exploit this phenomenon by causing a
pseudo-potential well to be formed along the central axis of
the ion guide so that ions are confined radially within the
ion guide.
It is known to use an RF ion guide to confine ions
radially and to subject the ions to Collision Induced
Dissociation or fragmentation within the ion guide.
Fragmentation of ions is typically carried out at pressures
in the range 10-3-10-1 mbar either within an RF ion guide or
within a dedicated gas collision cell.
It is also known to use an RF ion guide to confine ions
radially within an ion mobility separator or spectrometer.
Ion mobility separation may be carried out at atmospheric
pressure or at pressures in the range 10-1-101 mbar.
Different faults of RF ion guide are known including a
multi-pole rod set ion guide and a ring stack or ion tunnel
ion guide. A ring stack or ion tunnel ion guide comprises a
stacked ring electrode set wherein opposite phases of an RF
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voltage are applied to adjacent electrodes. A pseudo-
potential well is formed along the central axis of the ion
guide so that ions are confined radially within the ion
guide. The ion guide has a relatively high transmission
efficiency.
An RF ion guide is disclosed in US 2005/0253064 wherein
an RF voltage is applied to an elongated rod set in order to
confine ions radially within the ion guide. A static axial
electric field is arranged to propel ions along the axis of
the ion guide. An RF axial eleCtric field is also arranged
at the exit of the ion guide. The RF axial electric field
generates an axial pseudo-potential barrier which acts as a
barrier to ions. The magnitude of the pseudo-potential
barrier is inversely dependent upon the mass to charge ratio
of the ions. Therefore, ions having a relatively low mass to
charge ratio will experience a pseudo-potential barrier which
has a relatively large amplitude. The pseudo-potential
barrier counteracts the effect of the static axial field for
ions having relatively low mass to charge ratios but does not
counteract the effect of the static axial field upon ions
having relatively high mass to charge ratios. Accordingly,
ions having relatively high mass to charge ratios are ejected
from the ion guide. Ions may be manipulated within the ion
guide or may be mass selectively ejected by adjusting the
amplitude of the static or oscillating electric fields.
The known ion guide has a well-defined radial stability
condition for ions having a particular mass to charge ratio.
This is determined by the approximately quadratic nature of
the radial potential which is maintained. Therefore,
disadvantageously, if the oscillating electric field along
the axis of the ion guide is changed in any way then this may
cause undesired radial instabilities and/or resonance effects
which may result in ions being lost to the system.
It is therefore desired to provide an improved ion guide
or mass analyser.
According to an aspect of the present invention there is '
provided a mass analyser comprising:
an ion guide comprising a plurality of electrodes;
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means for applying a first AC or RF voltage to at least some
of said plurality of electrodes such that, in use, a plurality of
first axial time averaged or pseudo-potential barriers,
corrugations or wells having a first amplitude are created along at
least a portion of the axial length of said ion guide;
means for driving or urging ions along at least a portion of
the axial length of said ion guide; and
means for applying a second AC or RF voltage to one or more
of said plurality of electrodes such that, in use, one or more
second axial time averaged or pseudo-potential barriers,
corrugations or wells having a second amplitude are created along
at least a portion of the axial length of said ion guide, wherein
said second amplitude is different from said first amplitude;
wherein said means for driving or urging ions comprises means
for applying one or more transient DC voltages or potentials or one
or more DC voltage or potential waveforms to at least some of said
electrodes so that ions having mass to charge ratios within a first
range exit said ion guide whilst ions having mass to charge ratios
within a second range are axially trapped or confined within said
ion guide by said one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells.
In a mode of operation ions having mass to charge ratios M1
preferably exit the ion guide whilst ions having mass to charge
ratios < M2 are preferably axially trapped or confined within the
ion guide by the one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells. Preferably, M1 falls
with a first range which is preferably selected from the group
consisting of: (i) < 100; (ii) 100-200; (iii) 200-300; (iv) 300-
400; (v) 400-500; (vi) 500-600; (vii) 600-700; (viii) 700-800; (ix)
800-900; (x) 900-1000; and (xi) > 1000. Preferably, M2 falls with
a second range which is preferably selected from the group
consisting of: (i) < 100; (ii) 100-200; (iii) 200-300; (iv) 300-
400; (v) 400-500; (vi) 500-600; (vii) 600-700; (viii) 700-800; (ix)
800-900; (x) 900-1000; and (xi) > 1000. According to an embodiment
M1 and M2 may have the same value.
In a mode of operation ions are preferably sequentially
ejected from the mass analyser in order of their mass to charge
ratio or in reverse order of their mass to charge ratio.
According to the preferred embodiment the ion guide comprises
n axial segments, wherein n is selected from the group consisting
of: (i) 1-10; (ii) 11-20; (iii) 21-30; (iv)
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31-40; (v) 41-50; (vi) 51-60; (vii) 61-70; (viii) 71-80; (ix)
81-90; (x) 91-100; and (xi) > 100. Each axial segment
preferably comprises 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 15, 16, 17, 18, 19, 20 or > 20 electrodes. The axial
length of at least 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%,
80%, 90%, 95% or 100% of the axial segments is preferably
selected from the group consisting of: (i) < 1 mm; (ii) 1-2
Mm; (iii) 2-3 mm; (iv) 3-4 mm; (v) 4-5 mm; (vi) 5-6 mm; (vii)
6-7 mm; (viii) 7-8 mm; (ix) 8-9 mm; (x) 9-10 mm; and (xi)
10 mm. The spacing between at least 1%, 5%, 10%, 20%, 30%,
40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of the axial
segments is preferably selected from the group consisting of:
(i) < 1 mm; (ii) 1-2 mm; (iii) 2-3 mm; (iv) 3-4 mm; (v) 4-5
mm; (vi) 5-6 mm; (vii) 6-7 mm; (viii) 7-8 mm; (ix) 8-9 mm;
(x) 9-10 mm; and (xi) > 10 mm.
The ion guide preferably has a length selected from the
group consisting of: (i) < 20 mm; (ii) 20-40 mm; (iii) 40-60
mm; (iv) 60-80 mm; (v) 80-100 mm; (vi) 100-120 mm; (vii) 120-
140 mm; (viii) 140-160 mm; (ix) 160-180 mm; (x) 180-200 mm;
and (xi) > 200 mm.
The ion guide preferably comprises at least: (i) 10-20
electrodes; (ii) 20-30 electrodes; (iii) 30-40 electrodes;
(iv) 40-50 electrodes; (v) 50-60 electrodes; (vi) 60-70
electrodes; (vii) 70-80 electrodes; (viii) 80-90 electrodes;
(ix) 90-100 electrodes; (x) 100-110 electrodes; (xi) 110-120
electrodes; (xii) 120-130 electrodes; (xiii) 130-140
electrodes; (xiv) 140-150 electrodes; or (xv) > 150
electrodes.
According to the preferred embodiment the plurality of
electrodes preferably comprises electrodes having apertures
through which ions are transmitted in use. At least 1%, 5%,
10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of
the electrodes preferably have substantially circular,
rectangular, square or elliptical apertures.
According to an embodiment at least 1%, 5%, 10%, 20%,
30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of the
electrodes have apertures which are substantially the same
size or which have substantially the same area. According to
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another embodiment at least 1%, 5%, 10%, 20%, 30%, 40%, 50%,
60%, 70%, 80%, 90%, 95% or 100% of the electrodes have
apertures which become progressively larger and/or smaller in
size or in area in a direction along the axis of the ion
guide.
According to the preferred embodiment at least 1%, 5%,
10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of
the electrodes preferably have apertures having internal
diameters or dimensions selected from the group consisting
of: (i) 1.0 mm; (ii) 2.0 mm; (iii) 3.0 mm; (iv) 4.0
mm; (v) 5.0 mm; (vi) 6.0 mm; (vii) 7.0
mm; (viii) 8.0
mm; (ix) 9.0 mm; (x) 10.0 mm; and (xi) > 10.0 mm.
At least 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,
90%, 95% or 100% of the electrodes are preferably spaced
apart from one another by an axial distance selected from the
group consisting of: (i) less than or equal to 5 mm; (ii)
less than or equal to 4.5 mm; (iii) less than or equal to 4
mm; (iv) less than or equal to 3.5 mm; (v) less than or equal
to 3 mm; (vi) less than or equal to 2.5 mm.; (vii) less than
or equal to 2 mm; (viii) less than or equal to 1.5 mm; (ix)
less than or equal to 1 mm; (x) less than or equal to 0.8 mm;
(xi) less than or equal to 0.6 mm; (xii) less than or equal
to 0.4 mm; (xiii) less than or equal to 0.2 mm; (xiv) less
than or equal to 0.1 mm; and (xv) less than or equal to 0.25
mm.
At least some of the plurality of electrodes preferably
comprise apertures and wherein the ratio of the internal
diameter or dimension of the apertures to the centre-to-
- centre axial spacing between adjacent electrodes is selected
from the group consisting of: (i) < 1.0; (ii) 1.0-1.2; (iii)
1.2-1.4; (iv) 1.4-1.6; (v) 1.6-1.8; (vi) 1.8-2.0; (vii) 2.0-
2.2; (viii) 2.2-2.4; (ix) 2.4-2.6; (x) 2.6-2.8; (xi) 2.8-3.0;
(xii) 3.0-3.2; (xiii) 3.2-3.4; (xiv) 3.4-3.6; (xv) 3.6-3.8;
(xvi) 3.8-4.0; (xvii) 4.0-4.2; (xviii) 4.2-4.4; (xix) 4.4-
4.6; (xx) 4.6-4.8; (xxi) 4.8-5.0; and (xxii) > 5Ø
At least 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,
90%, 95% or 100% of the electrodes preferably have a
thickness or axial length selected from the group consisting
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of: (i) less than or equal to 5 mm; (ii) less than or equal
to 4.5 mm; (iii) less than or equal to 4 mm; (iv) less than
or equal to 3.5 mm; (v) less than or equal to 3 mm; (vi) less
than or equal to 2.5 mm; (vii) less than or equal to 2 mm;
(viii) less than or equal to 1.5 mm; (ix) less than or equal
to 1 mm; (x) less than or equal to 0.8 mm; (xi) less than or
equal to 0.6 ram; (xii) less than or equal to 0.4 mm; (xiii)
less than or equal to 0.2 mm; (xiv) less than or equal to 0.1
= mm; and (xv) less than or equal to 0.25 mm.
According to another embodiment the ion guide may
comprise a segmented rod set ion guide. The ion guide may
comprise, for example, a segmented quadrupole, hexapole or
octapole ion guide or ion guide comprising more than eight
segmented rod sets. The ion guide preferably comprises a
plurality of electrodes having a cross-section selected from
the group consisting of: (i) approximately or substantially
circular cross-section; (ii) approximately or substantially
hyperbolic surface; (iii) an arcuate or part-circular cross-
section; (iv) an approximately or substantially rectangular
cross-section; and (v) an approximately or substantially
square cross-section.
According to an alternative embodiment the ion guide may
comprise a plurality of plate electrodes, wherein a plurality
of groups of plate electrodes are arranged along the axial
. length of the ion guide. Each group of plate electrodes
preferably comprises a first plate electrode and a second
plate electrode. The first and second plate electrodes are
preferably arranged substantially in the same plane and are
preferably arranged either side of the central longitudinal
axis of the ion guide. The mass analyser preferably further
comprises means for applying a DC voltage or potential to the
= first and second plate electrodes in order to confine ions in
a first radial direction within the ion guide.
Each group of electrodes preferably further comprises a
third plate electrode and a fourth plate electrode. The
third and fourth plate electrodes are preferably arranged
substantially in the same plane and are preferably arranged
either side of the central longitudinal axis of the ion guide
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in a different orientation to the first and second plate
electrodes. The means for applying an AC or RF voltage is
preferably arranged to apply an AC or RF voltage to the third,
and fourth plate electrodes in order to confine ions in a
second radial direction within the ion guide. The second
radial direction is preferably orthogonal to the first radial
direction.
The means for driving or urging ions preferably
comprises means for applying one more transient DC voltages
or potentials or one or more DC voltage or potential
=
waveforms to at least 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%,
70%, 80%, 90%, 95% or 100% of the electrodes. The one or
more transient DC voltages or potentials or the one or more
DC voltage or potential waveforms preferably create: (i) a
potential hill or barrier; (ii) a potential well; (iii)
multiple potential hills or barriers; (iv) multiple potential
wells; (v) a combination of a potential hill or barrier and a
potential well; or (vi) a Combination of multiple potential
hills or barriers and multiple potential wells.
The one or more transient DC voltage or potential
waveforms preferably comprise a repeating waveform or square
wave.
According to the preferred embodiment a plurality of
axial DC potential wells are preferably translated along the
length of the ion guide or a plurality of transient DC
potentials or voltages are progressively applied to
electrodes along the axial length of the ion guide.
According to an embodiment the mass analyser preferably
further comprises first means arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the amplitude, height or
depth of the one or more transient DC voltages or potentials
or the one or more DC voltage or potential waveforms.
The first means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
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a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the amplitude, height or
depth of the one or more transient DC voltages or potentials
or the one or more DC voltage or potential waveforms by
Volts over a time period tl. Preferably, xl is selected from
the group consisting of: (i) < 0.1 V; (ii) 0.1-0.2 V; (iii)
0.2-0.3 V; (iv) 0.3-0.4 V; (v) 0.4-0.5 V; (vi) 0.5-0.6 V;
(vii) 0.6-0.7 V; (viii) 0.7-0.8 V; (ix) 0.8-0.9 V; (x) 0.9-
1.0 V; (xi) 1.0-1.5 V; (xii) 1.5-2.0 V; (xiii) 2.0-2.5 V;
(xiv) 2.5-3.0 V; (xv) 3.0-3.5 V; (xvi) 3.5-4.0 V; (xvii) 4.0-
4.5 V; (xviii) 4.5-5.0 V; (xix) 5.0-5.5 V; (xx) 5.5-6.0 V;
(xxi) 6.0-6.5 V; (xxii) 6.5-7.0 V; (xxiii) 7.0-7.5 V; (xxiv)
7.5-8.0 V; (xxv) 8.0-8.5 V; (xxvi) 8.5-9.0 V; (xxvii) 9.0-9.5
V; (xxviii) 9.5-10.0 V; and (xxix) > 10.0 V. Preferably, t1
is selected from the group consisting of: (i) < 1 ms; (ii) 1-
10 ms; (iii) 10-20 ms; (iv) 20-30 ms; (v) 30-40 ms; (vi) 40-
50 ms; (vii) 50-60 ms; (viii) 60-70 ms; (ix) 70-80 ms; (x)
80-90 ms; (xi) 90-100 ms; (xii) 100-200 ms; (xiii) 200-300
ms; (xiv) 300-400 ms; (xv) 400-500 ms; (xvi) 500-600 ms;
(xvii) 600-700 ms; (xviii) 700-800 ms; (xix) 800-900 ms; 000
900-1000 ms; (xxi) 1-2 s; (xxii) 2-3 s; (xxiii) 3-4 s; (xxiv)
4-5 s; and (xxv) > 5 s.
The mass analyser preferably comprises secOnd means
arranged and adapted to progressively increase, progressively
decrease, progressively vary, scan, linearly increase,
linearly decrease, increase in a stepped, progressive or
other manner or decrease in a stepped, progressive or other
manner the velocity or rate at which the one or more
transient DC voltages or potentials or the one or more DC
. 30 potential or. voltage waveforms are applied to the electrodes.
The second means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the velocity or rate at
which the one or more transient DC voltages or potentials or
the one or more DC voltage or potential waveforms are applied
to the electrodes by x2 m/s over a time period t2. Preferably,
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x2 is selected from the group consisting of: (i) < 1; (ii) 1-
2; (iii) 2-3; (iv) 3-4; (v) 4-5; (vi) 5-6; (vii) 6-7; (viii)
7-8; (ix) 8-9; (x) 9-10; (xi) 10-11; (xii) 11-12; (xiii) 12-
13; (xiv) 13-14; (xv) 14-15; (xvi) 15-16; (xvii) 16-17;
(xviii) 17-18; (xix) 18-19; (xx) 19-20; (xxi) 20-30; (xxii)
30-40; (xxiii) 40-50; (xxiv) 50-60; (xxv) 60-70; (xxvi) 70-
80; (xxvii) 80-90; (xxviii) 90-100; (xxix) 100-150; (xxx)
150-200; (xxxi) 200-250; (xxxii) 250-300; (xxxiii) 300-350;
(xxxiv) 350-400; (xxxv) 400-450; (xxxvi) 450-500; and
(xxxvii) > 500. Preferably, t2 is selected from the group-
consisting of: (i) < 1 ms; (ii) 1-10 ms; (iii) 10-20 ms; (iv)
20-30 ms; (v) 30-40 ms; (vi) 40-50 ms; (vii) 50-60 ms; (viii)
60-70 ms; (ix) 70-80 ms; (x) 80-90 ms; (xi) 90-100 ms; (xii)
100-200 ms; (xiii) 200-300 ms; (xiv) 3007400 ms; (xv) 400-500
ms; (xvi) 500-600 ms; (xvii) 600-700 ms; (xviii) 700-800 ms;
(xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s; (xxii) 2-3 .
S; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 s.
According to the preferred embodiment the first AC or RF
voltage preferably has an amplitude selected from the group
consisting of: (i) ,< 50 V peak to peak; (ii) 50-100 V peak to
peak; (iii) 100-150 V peak to peak; (iv) 150-200 V peak to
peak; (v) 200-250 V peak to peak; (vi) 250-300 V peak to
peak; (vii) 300-350 V peak to peak; (viii) 350-400 V peak to
peak; (ix) 400-450 V peak to peak; (x) 450-500 V peak to
peak; (xi) 500-550 V peak to peak; (xxii) 550-600 V peak to
peak; (xxiii) 600-650 V peak to peak; (xxiv) 650-700 V peak
to peak; (xxv) 700-750 V peak to peak; (xxvi) 750-800 V peak
to peak; (xxvii) 800-850 V peak to peak; (xxviii) 850-900 V
peak to peak; (xxix) 900-950 V peak to peak; (3000 950-1000 V
peak to peak; and (xxxi) > 1000 V peak to peak.
According to the preferred embodiment the first AC or RF
voltage preferably has a frequency selected from the group
consisting of: (i) < 100 kHz; (ii) 100-200 kHz; (iii) 200-300
kHz; (iv) 300-400 kHz; (v) 400-500 kHz; (vi) 0.5-1.0 MHz;
(vii) 1.0-1.5 MHz; (viii) 1.5-2.0 MHz; (ix) 2.0-2.5 MHz; (x)
2.5-3.0 MHz; (xi) 3.0-3.5 MHz; (xii) 3.5-4.0 MHz? (xiii) 4.0-
4.5 MHz; (xiv) 4.5-5.0 MHz; (xv) 5.0-5.5 MHz; (xvi) 5.5-6.0
MHz; (xvii) 6.0-6.5 MHz; (xviii) 6.5-7.0 MHz; (xix) 7.0-7.5
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MHz ; (xx) 7.5-8.0 MHz; (xxi) 8.0-8.5 MHz; (xxii) 8.5-9.0 MHz;
(xxiii) 9.0-9.5 MHz; (xxiv) 9.5-10.0 MHz; and (xxv) > 10.0
MHz.
The means for applying the first AC or RF voltage is
preferably arranged to apply the first AC or RF voltage to at
least 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,
55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the
plurality of electrodes.
The means for applying the first AC or RF voltage is
preferably arranged to supply axially adjacent electrodes or
axially adjacent groups of electrodes with opposite phases of
the first AC or RF voltage.
The first axial time averaged or pseudo-potential
barriers, corrugations or wells are preferably created, in
use, along at least 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%,
70%, 80%, 90% or 95% of the axial length of the ion guide.
The plurality of first axial time averaged or pseudo-
potential barriers, corrugations or wells are preferably
created or provided along at least 1%, 5%, 10%, 20%, 30%,
40%, 50%, 60%, 70%, 80%, 90% or 95% of the central
longitudinal axis of the ion guide.
The plurality of first axial time averaged or pseudo-
potential barriers, corrugations or wells are preferably
created or provided at an upstream portion and/or an
inteLmediate portion and/or a downstream portion of the ion
guide.
According to an embodiment the ion guide preferably has
a length L and the plurality of first axial time averaged or
pseudo-potential barriers, corrugations or wells are
preferably created or provided at one or more regions or
locations having a displacement along the length of the ion
guide selected from the group consisting of: (i) 0-0.1 L;
(ii) 0.1-0.2 L; (iii) 0.2-0.3 L; (iv) 0.3-0.4 L; (v) 0.4-0.5
L; (vi) 0.5-0.6 L; (vii) 0.6-0.7 L; (viii) 0.7-0.8 L; (ix)
0.8-0.9 L; and (x) 0.9-1.0 L.
The plurality of first axial time averaged or pseudo-
potential barriers, corrugations or wells preferably extend
at least r mm in a radial direction away from the central
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longitudinal axis of the ion guide, wherein r is selected
from the group consisting of: (i) < 1; (ii) 1-2; (iii) 2-3;
(iv) 3-4; (v) 4-5; (vi) 5-6; (vii) 6-7; (viii) 7-8; (ix) 8-9;
(x) 9-10; and (xi) > 10.
According to an embodiment for ions having mass to
charge ratios falling within a range 1-100, 100-200, 200-300,
300-400, 400-500, 500-600, 600-700, 700-800, 800-900 or 900-
1000 the amplitude, height or depth of at least 1%, 5%, 10%,
20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of the
first axial time averaged or pseudo-potential barriers,
corrugations or wells is preferably selected from the group
consisting of: (i) < 0.1 V; (ii) 0.1-0.2 V; (iii) 0.2-0.3 V;
(iv) 0.3-0.4 V; (v) 0.4-0.5 V; (vi) 0.5-0.6 V; (vii) 0.6-0.7
V; (viii) 0.7-0.8 V; (ix) 0.8-0.9 V; (x) 0.9-1.0 V; (xi) 1.0-
1.5 V; (xii) 1.5-2.0 V; (xiii) 2.0-2.5 V; (xiv) 2.5-3.0 V;
(xv) 3.0-3.5 V; (xvi) 3.5-4.0 V; (xvii) 4.0-4.5 V; (xviii)
4.5-5.0 V; (xix) 5.0-5.5 V; (xx) 5.5-6.0 V; (xxi) 6.0-6.5 V;
(xxii) 6.5-7.0 V; (xxiii) 7.0-7.5 V; (xxiv) 7.5-8.0 V; (xxv)
8.0-8.5 V; (xxvi) 8.5-9.0 V; (xxvii) 9.0-9.5 V; (xxviii) 9.5-
10.0 V; and (xxix) > 10.0 V.
Preferably, at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10
first axial time averaged or pseudo-potential barriers,
corrugations or wells are provided or created, in use, per cm
along at least a portion of the axial length of the ion
guide.
The plurality of first axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have
minima along the axial length of the ion guide which
preferably correspond with the axial location of the
plurality of electrodes.
The plurality of first axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have
maxima along the axial length of the ion guide located at
axial locations which preferably correspond with
substantially 50% of the axial distance or separation between
neighbouring electrodes.
The plurality of first axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have
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minima and/or maxima which are substantially the same height,
depth or amplitude for ions having a particular mass to
charge ratio and wherein the minima and/or maxima preferably
have a periodicity which is substantially the same as or a
multiple of the axial displacement or separation of the
plurality of electrodes.
According to an embodiment the mass analyser preferably
comprises third means arranged and adapted to progressively
increase, progressively decrease, progressively vary, scan,
linearly increase, linearly decrease, increase in a stepped,
progressive or other manner or decrease in a stepped,
progressive or other manner the amplitude of the first AC or
RF voltage applied to the electrodes.
The third means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the amplitude of the
first AC or RF voltage by x3 Volts over a time period t3.
Preferably, x3 is selected from the group consisting of: (i) <
50 V peak to peak; (ii) 50-100 V peak to peak; (iii) 100-150
V peak to peak; (iv) 150-200 V peak to peak; (v) 200-250 V
peak to peak; (vi) 250-300 V peak to peak; (vii) 300-350 V
peak to peak; (viii) 350-400 V peak to peak; (ix) 400-450 V
peak to peak; (x) 450-500 V peak to peak; (xi) 500-550 V peak
to peak; (xxii) 550-600 V peak to peak; (xxiii) 600-650 V
peak to peak; (xxiv) 650-700 V peak to peak; (xxv) 700-750 V
peak to peak; (xxvi) 750-800 V peak to peak; (xxvii) 800-850
V peak to peak; (xxviii) 850-900 V peak to peak; (xxix) 900-
950 V peak to peak; (xxx) 950-1000 V peak to peak; and (xxxi)
> 1000 V peak to peak. Preferably, t3 is selected from the
group consisting of: (i) < 1 ms; (ii) 1-10 ms; (iii) 10-20
ms; (iv) 20-30 ms; (v) 30-40 ms; (vi) 40-50 ms; (vii) 50-60
ms; (viii) 60-70 ms; (ix) 70-80 ms; (x) 80-90 ms; (xi) 90-100
ms; (xii) 100-200 ms; (xiii) 200-300 ms; (xiv) 300-400 ms;
(xv) 400-500 ms; (xvi) 500-600 ms; (xvii) 600-700 ms; (xviii)
700-800 ms; (xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s;
(xxii) 2-3 s; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 s.
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The mass analyser preferablyfurther comprises fourth
means arranged and adapted to progressively increase,
progressively decrease, progressively vary, scan, linearly
increase, linearly decrease, increase in,a stepped,
progressive or other manner or decrease in a stepped,
progressive or other manner the frequency of the first RF or
AC voltage applied to the electrodes. The fourth means is
preferably arranged and adapted to progressively increase,
progressively decrease, progressively vary, scan, linearly
increase, linearly decrease, increase in a stepped,
progressive or other manner or decrease in a stepped,
progressive or other manner the frequency of the first RF or
AC voltage applied to the electrodes by x4 MHz over a time
period t4. Preferably, x4 is selected from the group
consisting of: (i) < 100 kHz; (ii) 100-200 kHz; 200-300
kHz; (iv) 300-400 kHz; (v) 400-500 kHz; (vi) 0.5-1.0 MHz;
(vii) 1.0-1.5 MHz; (viii) 1.5-2.0 MHz; (ix) 2.0-2.5 MHz; (x)
2.5-3.0 MHz; (xi) 3.0-3.5 MHz; (xii) 3.5-4.0 MHz; (xiii) 4.0-
4.5 MHz; (xiv) 4.5-5.0 MHz; (xv) 5.0-5.5 MHz; (xvi) 5.5-6.0
MHz; (xvii) 6.0-6.5 MHz; (xviii) 6.5-7.0 MHz; (xix) 7.0-7.5
MHz; (xx) 7.5-8.0 MHz; (xxi) 8.0-8.5 MHz; (xxii) 8.5-9.0 MHz;
(xxiii) 9.0-9.5 MHz; (xxiv) 9.5-10.0 MHz; and (xxv) > 10.0
MHz. Preferably, t4 is selected from the group consisting of:
(i) < 1 ms; (ii) 1-10 ms; (iii) 10-20 ms; (iv) 20-30 ms; (v)
30-40 ms; (vi) 40-50 ms; (vii) 50-60 ms; (viii) 60-70 ms;
(ix) 70-80 ms; (x) 80-90 ms; (xi) 90-100 ms; (xii) 100-200
ms; (xiii) 200-300 ms; (xiv) 300-400 ms; (xv) 400-500 ms;
(xvi) 500-600 ms; (xvii) 600-700 ms; (xviii) 700-800 ms;
(xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s; (xxii) 2-3
s; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 s.
According to an embodiment the second AC or RF voltage
preferably has an amplitude selected from the group
consisting of: (i) < 50 V peak to peak; (ii) 50-100 V peak to
peak; (iii) 100-150 V peak to peak; (iv) 150-200 V peak to
peak; (v) 200-250 V peak to peak; (vi) 250-300 V peak to
peak; (vii) 300-350 V peak to peak; (viii) 350-400 V peak to
peak; (ix) 400-450 V peak to peak; (x) 450-500 V peak to
= peak; (xi) 500-550 V peak to peak; (xxii) 550-600 V peak to
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peak; (xxiii) 600-650 V peak to peak; (xxiv) 650-700 V peak
to peak; (xxv) 700-750 V peak to peak; (xxvi) 750-800 V peak
to peak; (xxvii) 800-850 V peak to peak; (xxviii) 850-900 V
peak to peak; (xxix) 900-950 V peak to peak; (xoo() 950-1000 V
peak to peak; and (xxxi) > 1000 V peak to peak.
The second AC or RF voltage preferably has a frequency
selected from the group consisting of: (i) < 100 kHz; (ii)
100-200 kHz; (iii) 200-300 kHz; (iv) 300-400 kHz; (v) 400-500
kHz; (vi) 0.5-1.0 MHz; (vii) 1.0-1.5 MHz; (viii) 1.5-2.0 MHz;
(ix) 2.0-2.5 MHz; (x) 2.5-3.0 MHz; (xi) 3.0-3.5 MHz; (xii)
3.5-1.0 MHz; (xiii) 4.0-4.5 MHz; (xiv) 4.5-5.0 MHz; (xv) 5.0-
5,5 MHz; (xvi) 5.5-6.0 MHz; (xvii) 6.0-6.5 MHz; (xviii) 6.5-
7,0 MHz; (xix) 7.0-7.5 MHZ; 0o0 7.5-8.0 MHz; (xxi) 8.0-8.5
MHz; (xxii) 8.5-9.0 MHz; (xxiii) 9.0-9.5 MHz; (xxiv) 9.5-10.0
MHz; and (xxv) > 10.0 MHz.
The means for applying the second AC or RF voltage is
preferably arranged to apply the second AC or RF voltage to
at least 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,
55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the
plurality of electrodes and/or at least 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38,
39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or > 50 of the
plurality of electrodes.
The means for applying the second AC or RF voltage is
preferably arranged to supply axially adjacent electrodes or
axiallY adjacent groups of electrodes with opposite phases of
the second AC or RF voltage.
The one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells are preferably
created, in use, along at least 1%, 5%, 10%, 20%, 30%, 40%,
50%, 60%, 70%, 80%, 90% or 95% of the axial length of the ion
guide.
The one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells are preferably
created or provided along at least 1%, 5%, 10%, 20%, 30%,
40%, 50%, 60%, 70%, 80%, 90% or 95% of the central
longitudinal axis of the ion guide.
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The plurality of second axial time averaged or pseudo-
potential barriers, corrugations or wells are preferably
created or provided at an upstream portion and/or an
intermediate portion and/or a downstream portion of the ion
guide.
The ion guide preferably has a length L and the
plurality of second axial time averaged or pseudo-potential
barriers, corrugations or wells are preferably created or
provided at one or more regions or locations having a
displacement along the length of the ion guide selected from
the group consisting of: (i) 0-0.1 L; (ii) 0.1-0.2 L; (iii)
0.2-0.3 L; (iv) 0.3-0.4 L; (v) 0.4-0.5 L; (vi) 0.5-0.6 L;
(vii) 0.6-0.7 L; (viii) 0.7-0.8 L; (ix) 0.8-0.9 L; and (x)
0.9-1.0 L.
The one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells preferably extend
at least r mm in a radial direction away from the central
longitudinal axis of the ion guide, wherein r is selected
from the group consisting of: (i) < 1; (ii) 1-2; (iii) 2-3;
(iv) 3-4; (v) 4-5; (vi) 5-6; (vii) 6-7; (viii) 7-8; (ix) 8-9;
(x) 9-10; and (xi) > 10.
According to an embodiment for ions having mass to
charge ratios falling within a range 1-100, 100-200, 200-300,
300-400, 400-500, 500-600, 600-700, 700-800, 800-900 or 900-
1000 the amplitude, height or depth of at least 1%, 5%, 10%,
20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of the
one or more second axial time averaged or pseudo-potential
barriers, corrugations or wells is preferably selected from
the group consisting of: (i) < 0.1 V; (ii) 0.1-0.2 V; (iii)
0.2-0.3 V; (iv) 0.3-0.4 V; (v) 0.4-0.5 V; (vi) 0.5-0.6 V;
(vii) 0.6-0.7 V; (viii) 0.7-0.8 V; (ix) 0.8-0.9 V; (x) 0.9-
1.0 V; (xi) 1.0-1.5 V; (xii) 1.5-2.0 V; (xiii) 2.0-2.5 V;
(xiv) 2.5-3.0 V; (xv) 3.0-3.5 V; (xvi) 3.5-4.0 V; (xvii) 4.0-
4.5 V; (xviii) 4.5-5.0 V; (xix) 5.0-5.5 V; (xx) 5.5-6.0 V;
(xxi) 6.0-6.5 V; (xxii) 6.5-7.0 V; (xxiii) 7.0-7.5 V; (xxiv)
7.5-8.0 V; (xxv) 8.0-8.5 V; (xxvi) 8.5-9.0 V; (xxvii) 9.0-9.5
V; (xxviii) 9.5-10.0 V; and (xxix) > 10.0 V.
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Preferably, at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 of
the second axial time averaged or pseudo-potential barriers,
corrugations or wells are provided or created, in use, per cm
along the axial length of the ion guide.
The one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have
minima along the axial length of the ion guide which
correspond with the axial location of the plurality of
electrodes.
The one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have
maxima along the axial length of the ion guide located at
axial locations which preferably correspond with
substantially 50% of the axial distance or separation between
neighbouring electrodes.
The one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have
minima and/or maxima which are substantially the same height,
depth or amplitude for ions having a particular mass to
charge ratio. The minima and/or maxima preferably have a
periodicity which is preferably substantially the same as or
a multiple of the axial displacement or separation of the
plurality of electrodes.
According to the preferred embodiment the second
amplitude is preferably less than or greater than the first
amplitude. Preferably, the ratio of the second amplitude to
the first amplitude is selected from the group consisting of:
(i) < 1; (ii) > 1; (iii) 1-2; (iv) 2-3; (v) 3-4; (vi) 4-5;
(vii) 5-6; (viii) 6-7; (ix) 7-8; (x) 8-9; (xi) 9-10; (xii)
10-11; (xiii) 11-12; (xiv) 12-13; (xv) 13-14; (xvi) 14-15;
(xvii) 15-16; (xviii) 16-17; (xix) 17-18; (xx) 18-19; (xxi)
19-20; (xxii) 20-25; (xxiii) 25-30; (xxiv) 30-35; (xxv) 35-
40; (xxvi) 40-45; (xxvii) 45-50; (xxviii) 50-60; (xxix) 60-
70; (xxx) 70-80; (xxxi) 80-90; (xxxii) 90-100; and (xxxiii) >
100.
According to an embodiment the mass analyser further
comprises fifth means arranged and adapted to progressively
increase, progressively decrease, progressively vary, scan,
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linearly increase, linearly decrease, increase in a stepped,
progressive or other manner or decrease in a stepped,
progressive or other manner the amplitude of the second AC or
RF voltage applied to one or more of the plurality of
electrodes.
The fifth means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the amplitude of the
second AC or RF voltage by x5 Volts over a time period t5.
Preferably, xs is selected from the group consisting of: (i) <
50 V peak to peak; (ii) 50-100 V peak to peak; (iii) 100-150
V peak to peak; (iv) 150-200 V peak to peak; (v) 200-250 V
peak to peak; (vi) 250-300 V peak to peak; (vii) 300-350 V
peak to peak; (viii) 350-400 V peak to peak; (ix) 400-450 V '
peak to peak; (x) 450-500 V peak to peak; (xi) 500-550 V peak
to peak; (xxii) 550-600 V peak to peak; (xxiii) 600-650 V
peak to peak; (xxiv) 650-700 V peak to peak; (xxv) 700-750 V
peak to peak; (xxvi) 750-800 V peak to peak; (xxvii) 800-850
V peak to peak; (xxviii) 850-900 V peak to peak; (xxix) 900-
950 V peak to peak; (xxx) 950-1000 V peak to peak; and (xxxi)
> 1000 V peak to peak. Preferably, t5 is selected from the
group consisting of: (i) < 1 ms; (ii) 1-10 ms; (iii) 10-20
ms; (iv) 20-30 ms; (v) 30-40 ms; (vi) 40-50 ms; (vii) 50-60
ms; (viii) 60-70 ms; (ix) 70-80 ms; (x) 80-90 ms; (xi) 90-100
ms; (xii) 100-200 ms; (xiii) 200-300 ms; (xiv) 300-400 ms;
(xv) 400-500 ms; (xvi) 500-600 ms; (xvii) 600-700 ms; (xviii)
700-800 ms; (xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s;
(xxii) 2-3 s; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 s.
The mass analyser preferably further comprises sixth
means arranged and adapted to progressively increase,
progressively decrease, progressively vary, scan, linearly
increase, linearly decrease, increase in a stepped,
progressive or other manner or decrease in a stepped,
progressive or other manner the frequency of the second RF or
AC voltage applied to one or more of the plurality of
electrodes.
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The sixth means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan,- linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the frequency of the
second RF or AC voltage applied to the electrodes by x6 MHz
over a time period t6. Preferably, x6 is selected from the
group consisting of: (i) < 100 kHz; (ii) 100-200 kHz; (iii)
200-300 kHz; (iv) 300-400 kHz; (v) 400-500 kHz; (vi) 0.5-1.0
MHz; (vii) 1.0-1.5 MHz; (viii) 1.5-2.0 MHz; (ix) 2.0-2.5 MHz;
(x) 2.5-3.0 MHz; (xi) 3.0-3.5 MHz; (xii) 3.5-4.0 MHz; (xiii)
4.0-4.5 MHz; (xiv) 4.5-5.0 MHz; (xv) 5.0-5.5 MHz; (xvi) 5.5-
6.0 MHz; (xvii) 6.0-6.5 MHz; (xviii) 6.5-7.0 MHz; (xix) 7.0-
7.5 MHz; (xx) 7.5-8.0 MHz; (xxi) 8.0-8.5 MHz; (xxii) 8.5-9.0
MHz; (xxiii) 9.0-9.5 MHz; (xxiv) 9.5-10.0 MHz; and (xxv) >
10.0 MHz. Preferably, t6 is selected from the group
consisting of: (i) < 1 ms; (ii) 1-10 ms; (iii) 10-20 ms; (iv)
20-30 ms; (v) 30-40 ms; (vi) 40-50 ms; (vii) 50-60 ms; (viii)
60-70 ms; (ix) 70-80 ms; (x) 80-90 ms; (xi) 90-100 ms; (xii)
100-200 ms; (xiii) 200-300 ms; (xiv) 300-400 ms; (xv) 400-500
ms; (xvi) 500-600 ms; (xvii) 600-700 ms; (xviii) 700-800 ms;
(xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s; (xxii) 2-3
S; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 s.
The mass analyser preferably further comprises means for
applying a first DC voltage to one or more of the plurality
of electrodes such that, in use, the one or more second axial
time averaged or pseudo-potential barriers, corrugations or
wells preferably comprise a DC axial potential barrier or
well in combination with an axial time averaged or pseudo-
potential barrier or well.
According to an embodiment the mass analyser further
comprises seventh means arranged and adapted to progressively
increase, progressively decrease, progressively vary, scan,
linearly increase, linearly decrease, increase in a stepped,
progressive or other manner or decrease in a stepped,
progressive or other manner the amplitude of the first DC
voltage applied to one or more of the plurality of
electrodes.
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The seventh means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the amplitude of the
first DC voltage by x7 Volts over a time period t7.
Preferably, x7 is selected from the group consisting of: (i)
0.1 V; (ii) 0.1-0.2 V; (iii) 0.2-0.3 V; (iv) 0.3-0.4 V; (v)
0.4-0.5 V; (vi) 0.5-0.6 V; (vii) 0.6-0.7 V; (viii) 0.7-0.8 V;
(ix) 0.8-0.9 V; (x) 0.9-1.0 V; (xi) 1.0-1.5 V; (xii) 1.5-2.0
V; (xiii) 2.0-2.5 V; (xiv) 2.5-3.0 V; (xv) 3.0-3.5 V; (xvi)
3.5-4.0 V; (xvii) 4.0-4.5 V; (xviii) 4.5-5.0 V; (xix) 5.0-5.5
V; (xx) 5.5-6.0 V; (xxi) 6.0-6.5 V; (xxii) 6.5-7.0 V; (xxiii)
7.0-7.5 V; (xxiv) 7.5-8.0 V; (xxv) 8.0-8.5 V; (xxvi) 8.5-9.0
V; (xxvii) 9.0-9.5 V; (xxviii) 9.5-10.0 V; and (xxix) > 10.0
V. Preferably, t7 is selected from the group consisting of:
(i) < 1 ms; (ii) 1-10 ms; (iii) 10-20 ms; (iv) 20-30 ms; (v)
30-40 ms; (vi) 40-50 ms; (vii) 50-60 ms; (viii) 60-70 ms;
(ix) 70-80 ms; (x) 80-90 ms; (xi) 90-100 ms; (xii) 100-200
ms; (xiii) 200-300 ms; (xiv) 300-400 ms; (xv) 400-500 ms;
(xvi) 500-600 ms; (xvii) 600-700 ms; (xviii) 700-800 ms;
(xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s; (xxii) 2-3
S; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 s.
The mass analyser preferably further comprises means for
applying a third AC or RF voltage to one or more of the
plurality of electrodes such that, in use, one or more third
axial time averaged or pseudo-potential barriers,
corrugations or wells having a third amplitude are created
along at least a portion of the axial length of the ion
guide. The third amplitude is preferably different from the
first amplitude and/or the second amplitude. According to an
embodiment the third amplitude may be the same as the second
amplitude but different from the first amplitude.
The third AC or RF voltage preferably has an amplitude
selected from the group consisting of: (i) < 50 V peak to
peak; (ii) 50-100 V peak to peak; (iii) 100-150 V peak to
peak; (iv) 150-200 v peak to peak; (v) 200-250 V peak to
peak; (vi) 250-300 v peak to peak; (vii) 300-350 V peak to
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peak; (viii) 350-400 V peak to peak; (ix) 400-450 V peak to
peak; (x) 450-500 V peak to peak; (xi) 500-550 V peak to
peak; (xxii) 550-600 V peak to peak; (xxiii) 600-650 V peak
to peak; (xxiv) 650-700 V peak to peak; (xxv) 700-750 V peak
to peak; (xxvi) 750-800 V peak to peak; (xxvii) 800-850 V
peak to peak; (xxviii) 850-900 V peak to peak; (xxix) 900-950
V peak to peak; (xxx) 950-1000 V peak to peak; and (xxxi) >
1000 V peak to peak.
The third AC or RF voltage preferably has a frequency
selected from the group consisting of: (i) < 100 kHz; (ii)
100-200 kHz; (iii) 200-300 kHz; (iv) 300-400 kHz; (v) 400-500
=
kHz; (IA) 0.5-1.0 MHz; (vii) 1.0-1.5 MHz; (viii) 1.5-2.0 MHz;
(ix) 2.0-2.5 MHz; (x) 2.5-3.0 MHz; (xi) 3.0-3.5 MHz; (xii)
3.5-4.0 MHz; (xiii) 4.0-4.5 MHz; (xiv) 4.5-5.0 MHz; (xv) 5.0-
5.5 MHz; (xvi) 5.5-6.0 MHz; (xvii) 6.0-6.5 MHz; (xviii) 6.5-
7,0 MHz; (xix) 7.0-7.5 MHz; (xx) 7.5-8.0 MHz; (xxi) 8.0-8.5
MHz; (xxii) 8.5-9.0 MHz; (xxiii) 9.0-9.5 MHz; (xxiv) 9.5-10.0
MHz; and (xxv) > 10.0 MHz.
The means for applying the third AC or RF voltage is
preferably arranged to apply the third AC or RF voltage to at
least 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,
55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the
plurality of electrodes.
The means for applying the third AC or RF voltage is
preferably arranged to supply axially adjacent electrodes or
axially adjacent groups of electrodes with opposite phases of
the third AC or RF voltage.
The one or more third axial time averaged or pseudo-
potential barriers, corrugations or wells are preferably
created, in use, along at least 1%, 5%, 10%, 20%, 30%, 40%,
50%, 60%, 70%, 80%, 90% or 95% of the axial length of the ion
guide.
The one or more of third axial time averaged or Pseudo-
potential barriers, corrugations or wells are preferably
created or provided along at least 1%, 5%, 10%, 20%, 30%,
40%, 50%, 60%, 70%, 80%, 90% or 95% of the central
longitudinal axis of the ion guide.
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The one or more of third axial' time averaged or pseudo-
potential barriers, corrugations or wells are preferably
created or provided at an upstream portion and/or an
inteLmediate portion and/or a downstream portion of the ion
guide.
The ion guide preferably has a length L and the one or
more third axial time averaged or pseudo-potential barriers, .
corrugations or wells are preferably created or provided at
one or more regions or locations having a displacement along
the length of the ion guide selected from the group
consisting of: (i) 0-0.1 L; (ii) 0.1-0.2 L; (iii) 0.2-0.3 L;
(iv) 0.3-0.4 L; (v) 0.4-0.5 L; (vi) 0.5-0.6 L; (vii) 0.6-0.7
L; (viii) 0.7-0.8 L; (ix) 0.8-0.9 L; and (x) 0.9-1.0 L.
The one or more of third axial time averaged or pseudo-
potential barriers, corrugations or wells preferably extend
at least r mm in a radial direction away from the central
longitudinal axis of the ion guide, wherein r is selected
from the group consisting of: (i) < 1; (ii) 1-2; (iii) 2-3;
(iv) 3-4; (v) 4-5; (vi) 5-6; (vii) 6-7; (viii) 7-8; (ix) 8-9;
(x) 9-10; and (xi) > 10.
According to an embodiment for ions having mass to
charge ratios falling within a range 1-100, 100-200, 200-300,
300-400, 400-500, 500-600, 600-700, 700-800, 800-900 or 900-
1000 the amplitude, height or depth of at least 1%, 5%, 10%,
20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 100% of the
third axial time averaged or pseudo-potential barriers,
corrugations or wells is selected from the group consisting
of: (i) < 0.1 V; (ii) 0.1-0.2 V; (iii) 0.2-0.3 V; (iv) 0.3-
0.4 V; (v) 0.4-0.5 V; (vi) 0.5-0.6 V; (vii) 0.6-0.7 V; (viii)
0.7-0.8 V; (ix) 0.8-0.9 V; (x) 0.9-1.0 V; (xi) 1.0-1.5 V;
(xii) 1.5-2.0 V; (xiii) 2.0-2.5 V; (xiv) 2.5-3.0 V; (xv) 3.0-
3.5 V; (xvi) 3.5-4.0 V; (xvii) 4.0-4.5 V; (xviii) 4.5-5.0 V;
(xix) 5.0-5.5 V; (xx) 5.5-6.0 V; (xxi) 6.0-6.5 V; (xxii) 6.5-
7.0 V; (xxiii) 7.0-7.5 V; (xxiv) 7.5-8.0 V; (xxv) 8.0-8.5 V;
(xxvi) 8.5-9.0 V; (xxvii) 9.0-9.5 V; (xxviii) 9.5-10.0 V; and
(xxix) > 10.0 V.
According to an embodiment at least 1, 2, 3, 4, 5, 6, 7,
8, 9 or 10 third axial time averaged or pseudo-potential
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barriers, corrugations or wells are provided or created, in .
use, per cm along the axial length of the ion guide.
The one or more third axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have
minima along the axial length of the ion guide which
preferably correspond with the axial location of the
plurality of electrodes.
The one or more third axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have
maxima along the axial length of the ion guide located at
axial locations which preferably correspond with
substantially 50% of the axial distance or 'separation between
neighbouring electrodes.
The one or more third axial time averaged or pseudo-
potential barriers, corrugations or wells preferably have ,
minima and/or maxima which are substantially the same height,
depth or amplitude for ions having a particular mass to
charge ratio and wherein the minima and/or maxima have a
periodicity which is substantially the same as or a multiple
of the axial displacement or separation of the plurality of
electrodes.
The third amplitude is preferably less than or greater
than the first amplitude and/or the second amplitude. The
ratio of the third amplitude to the first amplitude is
preferably selected from the group consisting of: (i) < 1;
(ii) > 1; (iii) 1-2; (iv) 2-3; (v) 3-4; (vi) 4-5; (vii) 5-6;
(viii) 6-7; (ix) 7-8; (x) 8-9; (xi) 9-10; (xii) 10-11; (xiii)
11-12; (xiv) 12-13; (xv) 13-14; (xvi) 14-15; (xvii) 15-16;
(xviii) 16-17; (xix) 17-18; (xx) 18-19; (xxi) 19-20; (xxii)
20-25; (xxiii) 25-30; (xxiv) 30-35; (xxv) 35-40; (xxvi) 40-
45; (xxvii) 45-50; (xxviii) 50-60; (xxix) 60-70;. Opo0 70-80;
(xxxi) 80-90; (xxxii) 90-100; and (xxxiii) > 100.
The ratio of the third amplitude to the second amplitude
is preferably selected from the group consisting of: (i) < 1;
(ii) > 1; (iii) 1-2; (iv) 2-3; (v) 3-4; (vi) 4-5; (vii) 5-6;
(viii) 6-7; (ix) 7-8; (x) 8-9; (xi) 9-10; (xii) 10-11; (xiii)
11-12; (xiv) 12-13; (xv) 13-14; (xvi) 14-15; (xvii) 15-16;
(xviii) 16-17; (xix) 17-18; (xx) 18-19; (xxi) 19-20; (xxii)
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20-25; (xxiii) 25-30; (xxiv) 30-35; (xxv) 35-40; (xxvi) 40-
45; (xxvii) 45-50; (xxViii) 50-60; (xxix) 60-70; (xxx) 70-80;
(xxxi) 80-90; (xxxii) 90-100; and (xxxiii) > 100.
The mass analyser may further comprise eighth means
arranged and adapted to progressively increase, progressively
decrease, progressively vary, scan, linearly increase,
linearly decrease, increase in a stepped, progressive or
other manner or decrease in a stepped, progressive or other
manner the amplitude of the third AC or RF voltage applied to
the one or more of the plurality of electrodes.
The eighth means is preferably arranged and adapted to
=
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the amplitude of the
third AC or RF voltage by x8 Volts over a time period t8.
Preferably, x8 is selected from the group consisting of: (i) <
50 V peak to peak; (ii) 50-100 V peak to peak; (iii) 100-150
V peak to peak; (iv) 150-200 V peak to peak; (v) 200-250 V
peak to peak; (vi) 250-300 V peak to peak; (vii) 300-350 V
peak to peak; (viii) 350-400 V peak to peak; (ix) 400-450 V
peak to peak; (x) 450-500 V peak to peak; and (xi) > 500 V
peak to peak. Preferably, t8 is selected from the group
consisting of: (i) < 1 ms; (ii) 1-10 ms; (iii) 10-20 ms; (iv)
20-30 ms; (v) 30-40 ms; (vi) 40-50 ms; (vii) 50-60 ms; (viii)
60-70 ms; (ix) 70-80 ms; (x) 80-90 ms; (xi) 90-100 ms; (xii)
100-200 ms; (xiii) 200-300 ms; (xiv) 300-400 ms; (xv) 400-500
ms; (xvi) 500-600 ms; (xvii) 600-700 ms; (xviii) 700-800 ms;
(xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s; (xxii) 2-3
s; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 s.
' According to an embodiment the mass analyser preferably
further comprises ninth means arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the frequency of the
third RF or AC voltage applied to the one or more of the
plurality of electrodes.
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The ninth means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the frequency of the
third RF or AC voltage applied to one or more of the
plurality of electrodes by x9 MHz over a time period t9.
Preferably, x9 is selected from the group consisting of: (i) <
100 kHz; (ii) 100-200 kHz; (iii) 200-300 kHz; (iv) 300-400
kHz; (v) 400-500 kHz; (vi) 0.5-1.0 MHz; (vii) 1.0-1.5 MHz;
(viii) 1.5-2.0 MHz; (ix) 2.0-2.5 MHz; (x) 2.5-3.0 MHz; (xi)
3.0-3.5 MHz; (xii) 3.5-4.0 MHz; (xiii) 4.0-4.5 MHz; (xiv)
4.5-5.0 MHz; (xv) 5.0-5.5 MHz; (xvi) 5.5-6.0 MHz; (xvii) 6.0-
6.5 MHz; (xviii) 6.5-7.0 MHz; (xix) 7.0-7.5 MHz; (xx) 7.5-8.0
MHz; (xxi) 8.0-8.5 MHz; (xxii) 8.5-9.0 MHz; (xxiii) 9.0-9.5
MHz; (xxiv) 9.5-10.0 MHz; and (xxv) > 10.0 MHz. Preferably,
t9 is selected from the group consisting of: (i) < 1 ms; (ii)
1-10 ms; (iii) 10-20 ms; (iv) 20-30 ms; (v) 30-40 ms; (vi)
40-50 ms; (vii) 50-60 ms; (viii) 60-70 ms; (ix) 70-80 ms; (x)
80-90 ms; (xi) 90-100 ms; (xii) 100-200 ms; (xiii) 200-300
ms; (xiv) 300-400 ms; (xv) 400-500 ms; (xvi) 500-600 ms;
(xvii) 600-700 ms; (xviii) 700-800 ms; (xix) 800-900 ms; (xx)
900-1000 ms; (xxi) 1-2 s; (xxii) 2-3 s; (xxlii) 3-4 s; (xxiv)
4-5 s; and (xxv) > 5 s.
The mass analyser preferably further comprises means for
applying a second DC voltage to one or more of the plurality
of electrodes such that, in use, the one or more third axial
time averaged or pseudo-potential barriers, corrugations or
wells comprise a DC axial potential barrier or well in
combination with an axial time averaged or pseudo-potential
barrier or well.
The mass analyser preferably further comprises tenth
means arranged and adapted to progressively increase,
progressively decrease, progressively vary, scan, linearly
increase, linearly decrease, increase in a stepped,
progressive or other manner or decrease in a stepped,
progressive or other manner the amplitude of the second DC
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voltage applied to one or more of the plurality of
electrodes.
The tenth means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the amplitude of the
second DC voltage by xn Volts over a time period tn.
Preferably, xn is selected from the group consisting of: (i)
< 0.1 V; (ii) 0.1-0.2 V; (iii) 0.2-0.3 V; (iv) 0.3-0.4 V; (v)
0.4-0.5 V; (vi) 0.5-0.6 V; (vii) 0.6-0.7 V; (viii) 0.7-0.8 V;
(ix) 0.8-0.9 V; (x) 0.9-1.0 V; (xi) 1.0-1.5 V; (xii) 1.5-2.0
V; (xiii) 2.0-2.5 V; (xiv) 2.5-3.0 V; (xv) 3.0-3.5 V; (xvi)
3.5-4.0 V; (xvii) 4.0-4.5 V; (xviii) 4.5-5.0 V; (xix) 5.0-5.5
V; (xx) 5.5-6.0 V; (xxi) 6.0-6.5 V; (xxii) 6.5-7.0 V; (xxiii)
7.0-7.5 V; (xxiv) 7.5-8.0 V; (xxv) 8.0-8.5 V; (xxvi) 8.5-9.0
V; (xxvii) 9.0-9.5 V; (xxviii) 9.5-10.0 V; and (xxix) > 10.0
V. Preferably, tn is selected from the group consisting of:
(i) < 1 ms; (ii) 1-10 ms; (iii) 10-20 ms; (iv) 20-30 ms; (v)
30-40 ms; (vi) 40-50 ms; (vii) 50-60 ms; (viii) 60-70 ms;
(ix) 70-80 Ms; (x) 80-90 ms; (xi) 90-100 ms; (xii) 100-200
ms; (xiii) 200-300 ms; (xiv) 300-400 ms; (xv) 400-500 ms;
(xvi) 500-600 ms; (xvii) 600-700 ms; (xviii) 700-800 ms;
(xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s; (xxii) 2-3
s; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 S.
According to an embodiment the mass analyser further
comprises eleventh means arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the amplitude of a DC
voltage or potential applied to at least some of the
electrodes of the ion guide and which acts to confine ions in
a radial direction within the ion guide.
The eleventh means is preferably arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
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stepped, progressive or other manner the amplitude of the DC
voltage or potential applied to the at least some electrodes
by xn Volts over a time period tn. Preferably, xn is
selected from the group consisting of: (i) < 0.1 V; (ii) 0.1-
0.2 V; (iii) 0.2-0.3 V; (iv) 0.3-0.4 V; (v) 0.4-0.5 V; (vi)
0.5-0.6 V; (vii) 0.6-0.7 V; (viii) 0.7-0.8 V; (ix) 0.8-0.9 V;
(x) 0.9-1.0 V; (xi) 1.0-1.5 V; (xii) 1.5-2.0 V; (xiii) 2.0-
2.5 V; (xiv) 2.5-3.0 V; (xv) 3.0-3.5 V; (xvi) 3.5-4.0 V;
(xvii) 4.0-4.5 V; (xviii) 4.5-5.0 V; (xix) 5.0-5.5 V; 0o0
5.5-6.0 V; (xxi) 6.0-6.5 V; (xxii) 6.5-7.0 V; (xxiii) 7.0-7.5
V; (xxiv) 7.5-8.0 V; (xxv) 8.0-8.5 V; (xxvi) 8.5-9.0 V;
(xxvii) 9.0-9.5 V; (xxviii) 9.5-10.0 V; and (xxix) > 10.0 V.
Preferably, tn is selected from the group consisting of: (i)
< 1 ms; (ii) 1-10 ms; (iii) 10-20 ms; (iv) 20-30 ms; (v) 30-
40 ms; (vi) 40-50 ms; (vii) 50-60 ms; (viii) 60-70 ms; (ix)
70-80 ms; (x) 80-90 ms; (xi) 90-100 ms; (xii) 100-200 ms;
(xiii) 200-300 ms; (xiv) 300-400 ms; (xv) 400-500 ms; (xvi)
500-600 ms; (xvii) 600-700 ms; (xviii) 700-800 ms; (xix) 800-
900 ms; (xx) 900-1000 ms; (xxi) 1-2 s; (xxii) 2-3 s; (xxiii)
3-4 s; (xxiv) 4-5 s; and (xxv) > 5 s.
The mass analyser preferably further comprises means for
maintaining in a mode of operation the ion guide at a
pressure selected from the group consisting of: (i) < 1.0 x
10-1 mbar; (ii) < 1.0 x 10-2 mbar; (iii) < 1.0 x 10-3 mbar; and
(iv) < 1.0 x 10-4 mbar.
The mass analyser preferably further comprises means for
maintaining in a mode of operation the ion guide at a
pressure selected from the group consisting of: (i) > 1.0 x
10-3 mbar; (ii) > 1.0 x 10-2 mbar; (iii) > 1.0 x 10-1 mbar;
(iv) > 1 mbar; (v) > 10 mbar; (vi) > 100 mbar; (vii) > 5.0 x
. 10-2 mbar; (viii) > 5.0 x 10-2 mbar; (ix) 10-4-10-3 mbar; (x) 10-
3-10-2 mbar; and (xi) 10-2-10-1 mbar.
The mass analyser preferably further comprises means
arranged and adapted to progressively increase, progressively
decrease, progressively vary, scan, linearly increase,
linearly decrease, increase in a stepped, progressive or
other manner or decrease in a stepped, progressive or other
manner the gas flow through the ion guide.
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According to an embodiment in a mode of operation ions
are preferably arranged to be trapped but are not
substantially fragmented within the ion guide.
The mass analyser may further comprise means for
collisionally cooling or substantially thermalising ions
within the ion guide.
The mass analyser may further comprise means for
substantially fragmenting ions within the ion guide in a mode
of operation.
The mass analyser may further comprise one or more
electrodes arranged at the entrance and/or exit of the ion
guide, wherein in 4 mode of operation the one or more
electrodes are arranged to pulse ions into and/or out of the
ion guide.
According to another aspect of the present invention
there is provided a mass spectrometer comprising a mass
analyser as discussed above.
The mass spectrometer preferably comprises an ion source
selected from the group consisting of: (i) an Electrospray
ionisation ("ESI") ion source; (ii) an Atmospheric Pressure
Photo Ionisation ("APPI") ion source; (iii) an Atmospheric
Pressure Chemical Ionisation ("APCI") ion source; (iv) a
Matrix Assisted Laser Desorption Ionisation ("MALDI") ion
source; (v) a Laser Desorption Ionisation ("LDI") ion source;
(vi) an Atmospheric Pressure Ionisation ("API") ion source;
(vii) a Desorption Ionisation on Silicon ("DIOS") ion source;
(viii) an Electron Impact ("El") ion source; (ix) a Chemical
Ionisation ("CI") ion source; (x) a Field Ionisation ("Fl")
ion source; (xi) a Field Desorption ("FD") ion source; (xii)
an Inductively Coupled Plasma ("ICP") ion source; (xiii) a
Fast Atom Bombardment ("FAB") ion source; (xiv) a Liquid
Secondary Ion Mass Spectrometry ("LSIMS") ion source; (xv) a
Desorption Electrospray Ionisation ("DESI") ion source; (xvi)
a Nickel-63 radioactive ion source; and (xvii) a Thermospray
ion source.
The mass spectrometer preferably comprises a continuous
or pulsed ion source.
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The mass spectrometer preferably further comprises one
or more mass filters arranged upstream and/or downstream of
the mass analyser. The one or more mass filters are
preferably selected from the group consisting of: (i) a
quadrupole rod set mass filter; (ii) a Time of Flight mass
filter or mass analyser; (iii) a Wein filter; and (iv) a
magnetic sector mass filter or mass analyser.
The mass spectrometer preferably further comprises one
or more second ion guides or ion traps arranged upstream
and/or downstream of the mass analyser. The one or more
second ion guides or ion traps are preferably selected from
the group consisting of:
(i) a multipole rod set or a segmented multipole rod set
ion guide or ion trap comprising a quadrupole rod set, a
hexapole rod set, an octapole rod set or a rod set comprising
more than eight rods;
(ii) an ion tunnel or ion funnel ion guide or ion trap
comprising a plurality of electrodes or at least 2, 5, 10,
20, 30, 40, 50, 60, 70, 80, 90 or 100 electrodes having
apertures through which ions are transmitted in use, wherein
at least 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,
55%, 60%, .65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the
electrodes have apertures which are of substantially the same
size or area or which have apertures which become
progressively larger and/or smaller in size or in area;
(iii) a stack or array of planar, plate or mesh
electrodes, wherein the stack or array of planar, plate or
mesh electrodes comprises a plurality or at least 2, 3, 4, 5,
6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20
planar, plate or mesh electrodes or at least 1%, 5%, 10%,
,15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%,
75%, 80%, 85%, 90%, 95% or 100% of the planar, plate or mesh
electrodes are arranged generally in the plane in which ions
travel in use; and
(iv) an ion trap or ion guide comprising a plurality of
groups of electrodes arranged axially along the length of the
ion trap or ion guide, wherein each group of electrodes
comprises: (a) a first and a second electrode and means for
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applying a DC voltage or potential to the first and second
electrodes in order to confine ions in a first radial
direction within the ion guide; and (b) a third and a fourth
electrode and means for applying an AC or RF voltage to the
third and fourth electrodes in order to confine ions in a
second radial direction within the ion guide, wherein the
second radial direction is preferably orthogonal to the first
radial direction.
According to a preferred embodiment the second ion guide
or ion trap preferably comprises an ion tunnel or ion funnel
ion guide or ion trap and wherein at least 1%, 5%, 10%, 15%,
20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%,
80%, 85%, 90%, 95% or 100% of the electrodes have internal
diameters or dimensions selected. from the group consisting
of: (i) 1.0 mm; (ii) 2.0 mm; (iii) 3.0 mm; (iv) 4.0
mm; (v) 5.0 mm; (vi) 6.0 mm; (vii) 7.0 mm; (viii) 8.0
mm; (ix) 9.0 mm; (x) -< 10.0 mm; and (xi) > 10.0 mm.
The second ion guide or ion trap preferably comprises
fourth AC or RF voltage means arranged and adapted to apply
an AC or RF voltage to at least 1%, 5%, 10%, 15%, 20%, 25%,
30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%,
90%, 95% or 100% of the plurality of electrodes of the second
ion guide or ion trap in order to confine ions radially
within the second ion guide or ion trap.
The second ion guide or ion trap is preferably arranged
and adapted to receive a beam or group of ions from the mass
analyser and to convert or partition the beam or group of
ions such that at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18, 19 or 20 separate packets of ions
are confined and/or isolated within the second ion guide or
ion trap at any particular time. Each packet of ions is
preferably separately confined and/or isolated in a separate
axial potential well formed in the second ion guide or ion
trap.
The mass spectrometer preferably further comprises means
arranged and adapted to urge at least some ions upstream
and/or downstream through or along at least 1%, 5%, 10%, 15%,
20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%,
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80%, 85%, 90%, 95% or 100% of the axial length of the second
ion guide or ion trap in a mode of operation.
According to an embodiment the mass spectrometer further
comprises transient DC voltage means arranged and adapted to
apply one or more transient DC voltages or potentials or one
or more transient DC voltage or potential waveforms to the
. electrodes forming the second ion guide or ion trap in order
to urge at least some ions downstream and/or upstream along
' at least 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,
55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the
axial length of the second ion guide or ion trap.
According to an embodiment the mass spectrometer
preferably further comprises AC or RF voltage means arranged
and adapted to apply two or more phase-shifted AC or RF
voltages to electrodes forming the second ion guide or ion
trap in order to urge at least some ions downstream and/or
upstream along at least 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%,
40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or
100% of the axial length of the second ion guide or ion trap.
The mass spectrometer preferably further comprises means
arranged and adapted to maintain at least a portion of the
second ion guide or ion trap at a pressure selected from the
group consisting of: (i) > 0.0001 mbar; (ii) > 0:001 mbar;
(iii) > 0.01 mbar; (iv) > 0.1 mbar; (v) > 1 mbar; (vi) > 10
mbar; (vii) > 1 mbar; (viii) 0.0001-100 mbar; and (ix) 0.001-
10 mbar.
The mass spectrometer may further comprise a collision,
fragmentation or reaction device arranged and adapted to
fragment ions by Collision Induced Dissociation ("CID").
According to another embodiment the mass spectrometer may
further comprise a collision, fragmentation or reaction
device selected from the group consisting of: (i) a Surface
Induced Dissociation ("SID") fragmentation device; (ii) an
Electron Transfer Dissociation fragmentation device; (iii) an
Electron Capture Dissociation fragmentation device; (iv) an
Electron Collision or Impact Dissociation fragmentation
device; (v) a Photo Induced Dissociation ("PID")
fragmentation device; (vi) a Laser Induced Dissociation
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fragmentation device; (vii) an infrared radiation induced
dissociation device; (viii) an ultraviolet radiation induced
dissociation device; (ix) a nozzle-skimmer interface
fragmentation device; (x) an in-source fragmentation device;
(xi) an ion-source Collision Induced Dissociation
fragmentation device; (xii) a theLmal or temperature source
fragmentation device; (xiii) an electric field induced
fragmentation device; (xiv) a magnetic field induced
fragmentation device; (xv) an enzyme digestion or enzyme
degradation fragmentation device; (xvi) an ion-ion reaction
fragmentation device; (xvii) an ion-molecule reaction
fragmentation device; (xviii) an ion-atom reaction
fragmentation device; (xix) an ion-metastable ion reaction
fragmentation device; (xx) an ion-metastable molecule
reaction fragmentation device; (xxi) an ion-metastable atom
reaction fragmentation device; (xxii) an ion-ion reaction
device for reacting ions to form adduct or product ions;
(xxiii) an ion-molecule reaction device for reacting ions to
= folm adduct or product ions; (xxiv) an ion-atom reaction
device for reacting ions to foim adduct or product ions;
(xxv) an ion-metastable ion reaction device for reacting ions
to folm adduct or product ions; (xxvi) an ion-metastable
molecule reaction device for reacting ions to form adduct or
product ions; and (xxvii) an ion-metastable atom reaction
device for reacting ions to form adduct or product ions.
According to an embodiment the mass spectrometer
preferably further comprises means arranged and adapted to
progressively increase, progressively decrease, progressively
vary, scan, linearly increase, linearly decrease, increase in
a stepped, progressive or other manner or decrease in a
stepped, progressive or other manner the potential difference
between the mass analyser and the collision, fragmentation or
reaction cell preferably during or over the cycle time of the
mass analyser.
According to an embodiment the mass spectrometer further
compidses a further mass analyser arranged upstream and/or
downstream of the mass analyser. The further mass analyser
is preferably selected from the group consisting of: (i) a
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Fourier Transform ("FT") mass analyser; (ii) a Fourier
Transform Ion Cyclotron Resonance ("FTICR") mass analyser;
(iii) a Time of Flight ("TOF") mass analyser; (iv) an
orthogonal acceleration Time of Flight ("oaTOF") mass
analyser; (v) an axial acceleration Time of Flight mass
analyser; (vi) a magnetic sector mass spectrometer; (vii) a
Paul or 3D quadrupole mass analyser; (viii) a 2D or linear
quadrupole mass analyser; (ix) a Penning trap mass analyser;
(x) an ion trap mass analyser; (xi) a Fourier Transform
orbitrap; (xii) an electrostatic Ion Cyclotron Resonance mass
spectrometer; (xiii) an electrostatic Fourier Transform mass
spectrometer; and (xiv) a quadrupole rod set mass filter or
mass analyser.
The mass spectrometer preferably further comprises means
arranged and adapted to progressively increase, progressively
decrease, progressively vary, scan, linearly increase,
linearly decrease, increase in a stepped, progressive or
other manner or decrease in a stepped, progressive or other
manner the mass to charge ratio transmission window of the
further analyser in synchronism with the operation of the
mass analyser during or over the cycle time of the mass
analyser.
According to an aspect of the present invention there is
provided a method of mass analysing ions comprising:
providing an ion guide comprising a plurality of
electrodes;
applying a first AC or RF voltage to at least some of
said plurality of electrodes such that a plurality of first
axial time averaged or pseudo-potential barriers,
corrugations or wells having a first amplitude are created
along at least a portion of the axial length of said ion
guide;
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applying a second AC or RF voltage to one or more of
said plurality of electrodes such that one or more second
axial time averaged or pseudo-potential barriers,
corrugations or wells having a second amplitude are created
along at least a portion of the axial length of said ion
guide, wherein said second amplitude is different from said
first amplitude; and
driving or urging ions along at least a portion of the
axial length of the ion guide by applying one or more
transient DC voltages or potentials or one or more DC voltage
or potential waveforms to at least some of said electrodes so
that ions having mass to charge ratios within a first range
exit said ion guide whilst ions having mass to charge ratios
within a second range are axially trapped or confined within
said ion guide by said one or more second axial time averaged
or pseudo-potential barriers, corrugations or wells.
According to an aspect of the present invention there is
provided a mass analyser comprising:
an ion guide comprising a plurality of electrodes, the
plurality of electrodes comprising electrodes having an
aperture through which ions are transmitted in use;
means for applying a first AC or RF voltage to at least
some of the plurality of electrodes so that axially adjacent
groups of electrodes are supplied with opposite phases of the
first AC or RF voltage and wherein, in use, a plurality of
first axial time averaged or pseudo-potential barriers,
corrugations or wells having a first amplitude are created
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along at least a portion of the axial length of the ion
guide; and
means for reversing the polarity of the first AC or RF
voltage applied to one or more axially adjacent groups of
electrodes such that, in use, one or more second axial time
averaged or pseudo-potential barriers, corrugations or wells
having a second amplitude are created along at least a
portion of the axial length of the ion guide, wherein the
second amplitude is different from the first amplitude.
Each group of electrodes may comprise 1, 2, 3, 4, 5, 6,
7, 8, 9, 10 or > 10 electrodes.
According to an aspect of the present invention there is
provided a method of mass analysing ions comprising:
providing an ion guide comprising a plurality of
electrodes, the plurality of electrodes comprising electrodes
having an aperture through which ions are transmitted;
applying a first AC or RF voltage to at least some of
the plurality of electrodes so that axially adjacent groups
of electrodes are supplied with opposite phases of the first
AC or RF voltage and wherein plurality of first axial time
averaged or pseudo-potential barriers, corrugations or wells
having a first amplitude are created along at least a portion
of the axial length of the ion guide; and
reversing the polarity of the first AC or RF voltage
applied to one or more axially adjacent groups of electrodes
such that one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells having a second
.amplitude are created along at least a portion of the axial
length of the ion guide, wherein the second amplitude is
different from the first amplitude.
According to an aspect of the present invention there is
provided a mass analyser comprising:
an ion guide comprising a plurality of electrodes, the
plurality of electrodes comprising electrodes having an
aperture through which ions are transmitted in use;
means for applying a first AC or RF voltage to at least
some of the plurality of electrodes so that axially adjacent
electrodes or axially adjacent groups of electrodes are
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supplied with opposite phases of the first AC or RF voltage
and wherein, in use, a plurality of first axial time averaged
or pseudo-potential barriers, corrugations or wells having a
first amplitude are created along at least a portion of the
axial length of the ion guide;
means for applying one or more transient DC voltages or
potentials or one or more transient DC voltage or potential
waveforms to the plurality of electrodes in order to drive or
urge ions along at least a portion of the axial length of the
ion guide;
means for reversing the polarity of the first AC or RF
voltage applied to a pair of axially adjacent electrodes or a
pair of axially adjacent groups of electrodes such that, in
use, one or more second axial time averaged or pseudo-
potential barriers, corrugations or wells having a second
amplitude are created along at least a portion of the axial
length of the ion guide, wherein the second amplitude is
different from the first amplitude; and
means for progressively decreasing in a linear or
stepped manner the amplitude of the first AC or RF voltage so
as to progressively reduce the amplitude of the one or more
second axial time averaged or pseudo-potential barriers,
corrugations or wells.
Preferably, the means for progressively decreasing the
amplitude of the first AC or RF voltage is arranged to
progressively decrease the amplitude of the first AC or RF
voltage by x12 Volts over a time period t2.2. Preferably, x12
is selected from the group consisting of: (i) < 50 V peak to
peak; (ii) 50-100 V peak to peak; (iii) 100-150 V peak to
peak; (iv) 150-200 V peak to peak; (v) 200-250 V peak to
peak; (vi) 250-300 V peak to peak; (vii) 300-350 V peak to
peak; (viii) 350-400 V peak to peak; (ix) 400-450 V peak to
peak; (x) 450-500 V peak to peak; (xi) 500-550 V peak to
peak; (xxii) 550-600 V peak to peak; (xxiii) 600-650 V peak
to peak; (xxiv) 650-700 V peak to peak; (xxv) 700-750 V peak
to peak; (xxvi) 750-800 V peak to peak; (xxvii) 800-850 V
peak to peak; (xxviii) 850-900 V peak to peak; (xxix) 900-950
V peak to peak; (xxx) 950-1000 V peak to peak; and (xxxi) >
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1000 V peak to peak. Preferably, t1.2 is selected from the
group consisting of: (i) < 1 ms; (ii) 1-10 ms; (iii) 10-20
ms; (iv) 20-30 ms; (v) 30-40 ms; (vi) 40-50 ms; (vii) 50-60
ms; (viii) 60-70 ms; (ix) 70-80 ms; (x) 80-90 ms; (xi) 90-100
ms; (xii) 100-200 ms; (xiii) 200-300 ms; (xiv) 300-400 ms;
(xv) 400-500 ms; (xvi) 500-600 ms; (xvii) 600-700 ms; (xviii)
700-800 ms; (xix) 800-900 ms; (xx) 900-1000 ms; (xxi) 1-2 s;
(xxii) 2-3 s; (xxiii) 3-4 s; (xxiv) 4-5 s; and (xxv) > 5 S.
According to an aspect of the present invention there is
provided a method of mass analysing comprising:
providing an ion guide comprising a plurality of
electrodes, the plurality of electrodes comprising electrodes
having an aperture through which ions are transmitted;
applying a first AC or RF voltage to at least some of
the plurality of electrodes so that axially adjacent
electrodes or axially adjacent groups of electrodes are
supplied with opposite phases of the first AC or RF voltage
and wherein a plurality of first axial time averaged or
pseudo-potential barriers, corrugations or wells having a
first amplitude are created along at least a portion of the
axial length of the ion guide;
applying one or more transient DC voltages or potentials
or one or more transient DC voltage or potential waveforms to
the plurality of electrodes in order to drive or urge ions
along at least a portion of the axial length of the ion
guide;
reversing the polarity of the first AC or RF voltage
applied to a pair of axially adjacent electrodes or a pair of
axially adjacent groups of electrodes such that one or more
second axial time averaged or pseudo-potential barriers,
corrugations or wells having a second amplitude are created
along at least a portion of the axial length of the ion
guide, wherein the second amplitude is different from the
first amplitude; and
progressively decreasing in a linear or stepped manner
the amplitude of the first AC or RF voltage so as to
progressively reduce the amplitude of the one or more second
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axial time averaged or pseudo-potential barriers,
corrugations or wells.
An ion guide or mass analyser is disclosed herein
comprising:
a plurality of electrodes;
means for applying a first AC or RF voltage to the
plurality of electrodes so that at least some electrodes are
maintained, in use, at opposite phases of the first AC or RF
voltage; and
means for varying, switching, changing or scanning the
phase difference or polarity of one or more electrodes so as
to create, in use, an axial time averaged or pseudo-potential
barrier along at least a portion of the axial length of the
ion guide or mass analyser.
The means for varying, switching, changing or scanning
the phase difference or polarity of the one or more
electrodes is preferably arranged to vary, switch, change or
scan the phase difference or polarity by 0 , wherein 0 is
selected from the group consisting of: (i) < 10; (ii) 10-20;
(iii) 20-30; (iv) 30-40; (v) 40-50; (vi) 50-60; (vii) 60-70;
(viii) 70-80; (ix) 80-90; (x) 90; (xi) 90-100; (xii) 100-110;
(xiii) 110-120; (xiv) 120-130; (xv) 130-140; (xvi) 140-150;
(xvii) 150-160; (xviii) 160-170; (xix) 170-180; and (xx) 180.
A method of guiding ions or mass analysing ions is
disclosed herein comprising:
providing an ion guide or mass analyser comprising a
plurality of electrodes;
applying a first AC or RF voltage to the plurality of
electrodes so that at least some electrodes are maintained at
opposite phases of the first AC or RF voltage; and
varying, switching, changing or scanning the phase
difference or polarity of one or more electrodes so as to
create an axial time averaged or pseudo-potential barrier
along at least a portion of the axial length of the ion guide
or mass analyser.
Preferably, the step of varying, switching, changing or
scanning the phase difference or polarity of the one or more
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electrodes comprises varying, switching, changing or scanning
the phase difference or polarity by 0 , wherein 0 is selected
from the group consisting of: (i) < 10; (ii) 10-20; (iii) 20-
30; (iv) 30-40; (v) 40-50; (vi) 50-60; (vii) 60-70; (viii)
70-80; (ix) 80-90; (x) 90; (xi) 90-100; (xii) 100-110; (xiii)
110-120; (xiv) 120-130; (xv) 130-140; (xvi) 140-150; (xvii)
150-160; (xviii) 160-170; (xix) 170-180; and (xx) 180.
According to a preferred embodiment of the present
invention an RF ion guide is provided which is arranged to
confine ions radially within the ion guide about a central
axis. One or more pseudo-potential barriers are preferably
maintained at one or more points along the central axis of
the ion guide. The magnitude of the one or more pseudo-
potential barriers preferably depends upon the mass to charge
ratio of an ion. The one or more pseudo-potential barriers
may be positioned at the entrance and/or at the exit of the
ion guide. Other embodiments are contemplated wherein one or
more pseudo-potential barriers may be located at one or more
positions along the length of the ion guide between the
entrance and the exit of the ion guide.
The RF ion guide preferably comprises a stack of annular
electrodes having apertures through which ions are
transmitted in use. Opposite phases of an RF voltage are
preferably applied to alternate electrodes in order to
confine ions radially within the ion guide. The ion guide
preferably comprises a ring stack or ion tunnel ion guide.
Ions are preferably propelled along and through the ion
guide by one or more transient DC voltages or potentials or
one or more transient DC voltage or potential waveforms which
are preferably applied to the electrodes of the ion guide.
If the amplitude of the one or more transient DC voltages or
potentials or the one or more transient DC voltage or
potential waveforms is substantially less than that of the
effective pseudo-potential barrier for ions having a
particular mass to charge ratio value, then these ions will
not be driven over or through the pseudo-potential barrier.
As a result, these ions will remain confined within the ion
guide. If the amplitude of the one or more transient DC
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voltages or potentials or the one or more transient DC
voltage or potential waveforms is substantially greater than
that of the effective pseudo-potential barrier for ions
having a particular mass to charge ratio value then these
ions will be driven over or through the pseudo-potential
barrier and hence will exit the ion guide.
Ions may be driven progressively over a pseudo-potential
barrier in decreasing order of their mass to charge ratio by
progressively increasing the amplitude of the one or more
transient DC voltage or potentials which is applied to the
electrodes of the ion guide and/or by decreasing the
effective amplitude of the pseudo-potential barrier. The
amplitude of the pseudo-potential barrier may be decreased by
reducing the amplitude of the applied RF voltage and/or by
increasing the frequency of the applied RF voltage.
According to another embodiment the pseudo-potential
barrier may be augmented by an additional DC potential
applied to electrodes in proximity to the pseudo-potential
barrier. According to this embodiment the amplitude of the
barrier is a combination of a mass to charge ratio dependent
pseudo-potential barrier and a mass to charge ratio
independent DC potential barrier. The amplitude of the
effective barrier may be decreased by reducing the amplitude
of the RF voltage and/or by increasing the applied frequency
of the applied RF voltage and/or by reducing the amplitude of
the applied DC potential. Ions, which are mass selectively
ejected from the ion guide in an axial manner may be
transmitted onwardly for further processing and/or analysis.
According to another embodiment the pseudo-potential
barrier may be arranged at the entrance of the ion guide such
that if ions having a particular mass to charge ratio have
sufficient axial energy then they will overcome the pseudo-
potential barrier and so enter the preferred ion guide. If
ions having a particular mass to charge ratio have
insufficient axial energy to overcome the pseudo-potential
barrier then they are preferably prevented from entering the
ion guide and hence are lost to the system. The preferred
ion guide may be used to affect a low-mass cut off
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characteristic. The characteristics of this low-mass cut off
may be altered by increasing the amplitude of the mass to
charge ratio dependent barrier and/or by increasing the axial
energy of the ions entering the ion guide.
According to a particularly preferred embodiment a first
AC or RF voltage may be applied to the electrodes so that
axially adjacent electrodes are maintained at opposite phases
of the first AC or RF voltage. The polarity of a pair of
electrodes may then be switched or reversed. At an instance
in time the polarity of a plurality of electrodes may
therefore be changed from +-+-+-+- to +-++--+-. As a result
the effective thickness of electrodes along a portion or
section of the ion guide is effectively increased.
Further embodiments are contemplated wherein a multi-
phase RF voltage may be applied to the electrodes. For
example, a three phase RF voltage may be applied wherein a
120 phase difference is maintained initially between adjacent
electrodes. A pseudo-potential barrier may be created by
altering the phase relationship between electrodes or of a
number of electrodes in a region or section of the ion guide
or mass analyser. For example, the phase relationship or
pattern along a section of the ion guide or mass analyser may
be changed from: 123 123 123 123 123 to being: 123 331 112
223 123. Again, according to this embodiment the effective
thickness of electrodes along a portion or section of the ion
guide or mass analyser is effectively increased. A pseudo-
potential barrier will therefore created at this region which
has an amplitude which is greater than the amplitude of the
pseudo-potential corrugations which are otherwise formed
along the length of the ion guide.
According to an aspect of the present invention there is
provided a mass analyser comprising:
a plurality of electrodes;
means for applying a n-phase AC or RF voltage to the
plurality of electrodes wherein n 2;
means for maintaining a first phase relationship or
first aspect ratio between, at or of the plurality of
electrodes; and
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means for changing the phase relationship or aspect
ratio between, at or of a sub-set of the plurality of
electrodes so that a second different phase relationship or
second aspect ratio is maintained between, at or of the sub-
set of electrodes so as to create, in use, one or more axial
time averaged or pseudo-potential barriers, corrugations or
wells along at least a portion of the axial length of the ion
guide or mass analyser.
Preferably, n is selected from the group consisting of:
(i) 2; (ii) 3; (iii) 4; (iv) 5; (v) 6; (vi) 7; (vii) 8;
(viii) 9; (ix) 10; and (x) > 10.
The first phase relationship or first aspect ratio
preferably has a first periodicity, pattern, sequence or
value and the second phase relationship or second aspect
ratio preferably has a second different periodicity, pattern,
sequence or value.
According to an aspect of the present invention there is
provided a method of guiding ions or mass analysing ions
comprising:
providing an ion guide or mass analyser comprising a
plurality of electrodes;
applying a n-phase AC or RF voltage to the plurality of
electrodes wherein n 2;
maintaining a first phase relationship or first aspect
ratio between the plurality of electrodes; and
changing the phase relationship or first aspect ratio
between, at or of a sub-set of the plurality of electrodes so
that a second different phase relationship or second aspect
ratio is maintained between, at or of the sub-set of
electrodes so as to create one or more axial time average or
pseudo-potential barriers, corrugations or wells along at
least a portion of the axial length of the ion guide or mass
analyser.
An ion guide or mass analyser is disclosed herein
comprising:
a plurality of electrodes;
means for applying a n-phase AC or RF voltage to the
plurality of electrodes wherein n 2; and
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means for scanning the phase or aspect ratio of one or
more of the plurality of electrodes so as to create, in use,
one or more axial time averaged or pseudo-potential barriers,
corrugations or wells along at least a portion of the axial
length of the ion guide or mass analyser.
A method of guiding ions or mass analysing ions is
disclosed herein comprising:
providing an ion guide or mass analyser comprising a
plurality of electrodes;
applying a n-phase AC or RF voltage to the plurality of
electrodes wherein n 2; and
scanning the phase or aspect ratio of one or more of the
plurality of electrodes so as to create, in use, one or more
axial time averaged or pseudo-potential barriers,
corrugations or wells along at least a portion of the axial
length of the ion guide or mass analyser.
According to this embodiment the phase of one or more
electrodes may be progressively varied or scanned. The phase
of the one or more electrodes may be scanned by at least 6 ,
wherein 0 is selected from the group consisting of: (i) < 10;
(ii) 10-20; (iii) 20-30; (iv) 30-40; (v) 40-50; (vi) 50-60;
(vii) 60-70; (viii) 70-80; (ix) 80-90; (x) 90; (xi) 90-100;
(xii) 100-110; (xiii) 110-120; (xiv) 120-130; (xv) 130-140;
(xvi) 140-150; (xvii) 150-160; (xviii) 160-170; (xix) 170-
180; and (xx) 180. As the phase of the one or more
electrodes is progressively varied or scanned then the height
of the one or more axial time averaged or pseudo-potential
barriers, corrugations or wells preferably increases or
decreases.
According to the preferred embodiment ions near the
centre of the stacked ring ion guide will have stable
trajectories for a wide range of conditions. This is in
contrast to the radial stability conditions for ions in a
quadrupole rod set wherein changing the nature of the
oscillating field along the axis of such a device may cause
undesired radial instabilities and/or resonances resulting in
losses of ions.
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Multi-pole rod sets are also relatively large and
expensive to manufacture compared to the barrier device or
mass analyser according to the preferred embodiment. The ion
guide or mass analyser according to the preferred embodiment
is therefore particularly advantageous compared with known
arrangements.
Various embodiments of the present invention will now be
described, by way of example only, and with reference to the
accompanying drawings in which:
Fig. 1 shows a stacked ring ion guide in the y,z plane
according to an embodiment of the present invention;
Fig. 2 shows a stacked ring ion guide in the x,y plane
according to an embodiment of the present invention;
Fig. 3A shows a plot of the axial pseudo-potential along
the central axis of an ion guide experienced by ions having a
mass to charge ratio of 100 and Fig. 3B shows a plot of the
axial pseudo-potential along the central axis of an ion guide
experienced by ions having a mass to charge ratio of 500;
Fig. 4 shows a three-dimensional plot of the axial and
radial pseudo-potential for the embodiment shown in Fig. 3A
and experienced by ions having a mass to charge ratio of 100;
Fig. 5 shows an embodiment of the present invention
wherein a mass to charge ratio dependant barrier is provided
at the exit of the preferred ion guide or mass analyser;
Fig. 6A shows a plot of the axial pseudo-potential along
the centre line of the ion guide or mass analyser as a
function of distance for an ion guide or mass analyser as
shown in Fig. 5 and as experienced by ions having a mass to
charge ratio of 100 and Fig. 6B shows a plot of the axial
pseudo-potential along the centre line of the ion guide or
mass analyser as a function of distance for the ion guide or
mass analyser shown in Fig. 5 and as experienced by ions
having a mass to charge ratio of 500;
Fig. 7 shows a three-dimensional plot of the axial and
radial pseudo-potential for the embodiment shown in Fig. 6A
and as experienced by ions having a mass to charge ratio of
100;
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Fig. 8 shows another embodiment of the present invention
wherein a mass to charge ratio dependant barrier is formed at
the exit of the ion guide or mass analyser and wherein the
exit electrodes are arranged to have relatively small
apertures;
Fig. 9A shows a further embodiment wherein a mass to
charge ratio dependant barrier is formed at the exit of the
ion guide or mass analyser and Fig. 9B shows the maximum and
minimum potential of an additional time varying potential
which is applied to the electrodes;
Fig. 10 shows an embodiment wherein a preferred ion
guide or mass analyser is coupled with a quadrupole rod set
mass analyser which is scanned in use;
Fig. 11 shows an embodiment wherein a preferred ion
guide or mass analyser is coupled to an orthogonal
acceleration Time of Flight mass analyser;
Fig. 12 shows an embodiment wherein a mass to charge
ratio dependant barrier is folmed at the entrance of a
preferred ion guide or mass analyser;
Fig. 13A shows a plot of the axial pseudo-potential
along the centre line of the ion guide or mass analyser as a
function of distance for an ion guide or mass analyser as
shown in Fig. 12 and as experienced by ions having a mass to
charge ratio of 100 and Fig. 13B shows a plot of,the axial
pseudo-potential along the centre line of the ion guide as a
function of distance for an ion guide or mass analyser as
shown in Fig. 12 and as experienced by ions having a mass to
charge ratio of 500;
Fig. 14, shows a three-dimensional plot of the axial and
radial pseudo-potential as shown in Fig. 13A as experienced
by ions having a mass to charge ratio of 100;
Fig. 15 shows an embodiment wherein an ion mobility
separation device is coupled to a preferred ion guide or mass
analyser;
Fig. 16 shows a plot of the mass to charge ratio of ions
as a function of drift time through an ion mobility device
showing a scan line for low mass cut-off operation;
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Fig. 17 shows an experimental arrangement which was used
to produce experimental data as shown in Figs. 18A-18E; and
Fig. 18A shows a mass spectrum obtained in the absence
of an axial pseudo-potential barrier, Fig. 18B shows a mass
spectrum obtained when an axial pseudo-potential barrier was
provided at the entrance to .a preferred ion guide or mass
analyser as shown in Fig. 17, Fig. 18C shows a resulting mass
spectrum obtained when the axial pseudo-potential barrier had
a magnitude which was greater than that used to obtain the
results shown in Fig. 18B, Fig. 18D shows a mass spectrum
obtained when the axial pseudo-potential barrier had a
magnitude which was greater than that used to obtain the
results shown in Fig. 18C and Fig. 18E shows a mass spectrum
obtained when the axial pseudo-potential barrier had a
magnitude which was greater than that used to obtain the
results shown in Fig. 18D.
An embodiment of the present invention will now be
described with reference to Fig. 1. According to this
embodiment a RF ring stack ion guide 2 is provided. The ion
guide preferably comprises an entrance plate or electrode 1
which is preferably held or maintained in use at a DC
potential and a plurality of other annular electrodes or ,
plates 2a. Opposite phases of a modulated (RF) potential are
preferably applied to alternate electrodes or plates 2a which
foLm the ion guide. The ion guide 2 preferably comprises an
exit plate or electrode 3 which is preferably held or
maintained in use at a DC potential.
According to the preferred embodiment an additional
transient DC potential 4 is preferably applied to one or more
of the ring electrodes 2a as shown. The transient DC
potential 4 is preferably applied to one or more electrodes
2a at the same time for a relatively short period of time.
The DC potential 4 is then preferably switched or applied to
one or more adjacent or subsequent electrodes 2a. According
to the preferred embodiment one or more transient DC
potentials or voltages or one or more transient DC voltage or
potential waveforms are preferably progressively applied to
some or all of the electrodes 2a of the ion guide 2 in order
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to urge ions in a particular direction along the length of
the ion guide 2.
The ion guide 2 preferably comprises a series of annular
electrodes 2a which preferably have an internal diameter of 5
mm. Fig. 2 shows the stacked ring ion guide 2 when viewed in
the x,y plane. Each electrode 2a is preferably 0.5 mm thick
and the centre-to-centre spacing between adjacent electrodes
is preferably 1.5 mm. The diameter of the aperture of the
entrance and exit electrode 1,3 is preferably 2 mm.
Fig. 3A shows a plot of the time averaged or pseudo-
potential along the central axis of the ion guide 2 as
experienced by ions having a mass to charge ratio of 100 when
a RF voltage having a maximum voltage of 100 V at a frequency
of 1 MHz is applied to the ion guide 2. Fig. 3B shows a
comparable plot of the time averaged or pseudo-potential
along the central axis of the ion guide 2 as experienced by
ions having a mass to charge ratio of 500.
The plots shown in Figs. 3A and 3B were obtained by
recording the voltage gradient within a three dimensional
computer simulation (SIMION) of an ion guide having a
geometry as shown in Fig. 1. A static DC voltage was applied
to each of the lens elements equivalent to the maximum
voltage during a frequency cycle. The pseudo-potentials were
then calculated directly from the recorded,field using the
equation:
qE
r= 2 (1)
4m122
wherein q is the total charge on the ion (z.e), e is the
electron charge, z is the number of charges, m is the atomic
mass of the ion, L--2 is the frequency of the modulated
potential and E is the electric field recorded.
Fig. 4 shows the radial and axial pseudo-potential
within a preferred ion guide 2 cut along the centre of the z-
axis for a region at the exit of the ion guide 2 and
extending from 0 to 1 mm in the x-axis (radial direction).
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The conditions of voltage and frequency are as previously
described for ions having a mass to charge ratio of 100.
It can be seen from Figs. 3A and 3B that the axial
pseudo-potential corrugations in the z axis are larger for
ions having a relatively low mass to charge ratio than for
ions having a relatively high mass to charge ratio. As is
apparent from Fig. 4, along the central axis the axial
pseudo-potential corrugations have a relatively low amplitude
compared with the amplitude of the pseudo-potential
corrugations at a radial displacement away from the central
axis. Ions may be propelled readily along the ion guide 2 by
applying one or more transient DC voltages or potentials or
one or more transient DC voltage or potential waveforms to
the electrodes 2a of the ion guide 2.
Fig. 5 shows an embodiment of the present invention
wherein the last two annular plates or electrodes 5a,5b
immediately prior to or upstream of the exit aperture 3 are
preferably driven by a second RF voltage supply which is
preferably different to the first RF voltage supply which is
preferably applied to the preceding annular plates or
electrodes 2a.
When the amplitude of the second RF voltage which is
preferably applied to one or both of the last two annular
plates or electrodes 5a,5b is increased with respect to the
amplitude of the first RF voltage applied to the other plates
or electrodes 2a, then the depth of the pseudo-potential
corrugations and hence the height of the pseudo-potential
barrier at the exit of the ion tunnel ion guide or mass
analyser 2 is preferably increased.
According to another embodiment the frequency of the
second RF modulation applied to one or both of the last two
annular plates or electrodes 5a,5b may be decreased with
respect to the frequency of modulation of the first RF
voltage applied to the other electrodes 2a of the ion guide
or mass analyser 2.
Fig. EA shows a plot of the time averaged or pseudo-
potential along the central axis of an ion guide or mass
analyser 2 as experienced by ions having a mass to charge
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ratio of 100 when a first RF voltage having a maximum
amplitude of 100 V and a frequency of 1 MHz is applied to
annular plates or electrodes 2a, an RF voltage having a
maximum amplitude of 400 V is applied to plate 5b (which is
arranged immediately upstream of exit electrode 3) and a
third RF voltage having a maximum amplitude of 200 V is
applied to plate 5a (which is arranged upstream of electrode
5b). The phase and frequency of the modulated potential
applied to all the plates or electrodes 2a,5a,5b was
identical. Fig. 6B shows the time averaged or pseudo-
potential along the central axis of the ion guide or mass
analyser 2 as experienced by ions having a higher mass to
charge ratio of 500.
Fig. 7 shows the radial and axial pseudo-potential
within the preferred ion guide or mass analyser 2 cut along
the centre of the z-axis for a region at the exit of the ion
guide or mass analyser 2 and extending from 0 to 1 mm in the
x-axis (radial direction). The conditions of voltage and
, frequency are as previously described with regard to Fig. 6A
for ions having a mass to charge ratio of 100.
The result of increasing the amplitude of the modulated
potential at the exit of the ion guide or mass analyser 2 is
to produce a pseudo-potential barrier which preferably has an
amplitude which is inversely proportional to the mass to
charge ratio of ions.
According to the preferred embodiment ions are
preferably introduced into the ion guide from an external ion
source. The ions may be introduced, for example, either in a
pulsed manner or in a continuous manner at a time To. As ions
are introduced, the axial energy of the ions entering the ion
guide or mass analyser 2 is preferably arranged such that all
ions having mass to charge ratios within a specific range are
confined by the radial RF field and are preferably prevented
from exiting the ion guide or mass analyser 2 due to the
presence of the pseudo-potential barrier.
The initial energy spread of ions confined within the
ion guide or mass analyser 2 may be reduced by introducing a
cooling gas into an ion confinement region of the ion guide
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or mass analyser 2. The ion guide or mass analyser 2 is
preferably maintained at a pressure in the range 10-5-101 mbar
or more preferably in the range 10-3-10-1 mbar. The kinetic
energy of the ions will preferably be reduced as a result of
collisions between ions with gas molecules. Ions will
therefore cool to thermal energies.
Once ions have been accumulated within the ion guide or
mass analyser 2 a DC voltage applied to the entrance
electrode 1 may be raised in order to prevent ions from
exiting the ion guide or mass analyser 2 via the entrance.
According to another embodiment one or more pseudo-
potential barriers may be formed at the entrance of the ion
guide or mass analyser 2 by applying one or more suitable
potentials to one or more annular plates or electrodes
arranged at the entrance of the ion guide or mass analyser 2.
At an initial time To one or more transient DC voltages
or potentials or one or more DC voltage or potential
wavefolms are preferably applied to the electrodes 2a forming
the ion guide or mass analyser 2. According to an embodiment
the amplitude of the one or more DC voltages or potentials or
one or more DC voltage or potential waveforms may be
relatively low or effectively zero initially. The amplitude
of the one or more transient DC voltages or potentials or one
or more DC voltage or potential wavefoims may then according
to one embodiment be progressively ramped, stepped up or
increased in amplitude to a final maximum value. Ions are
thus preferably propelled, urged or translated towards a
pseudo-potential barrier arranged at the exit of the ion
guide or mass analyser 2. Ions are preferably caused to exit
the ion guide or mass analyser 2 in reverse order of their
mass to charge ratio with ions having relatively high mass to
charge ratios exiting the ion guide or mass analyser 2 before
ions having relatively low mass to charge ratios. The
process may then be repeated once the ion guide or mass
analyser 2 has been emptied of ions.
Fig. 8 shows an embodiment wherein the diameter of the
two annular plates or electrodes 5a,5b arranged at the exit
of the ion guide or mass analyser 2 are preferably smaller
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than the diameter of the electrodes 2a comprising the rest of
the ion guide or mass analyser 2. A mass selective pseudo-
potential barrier is preferably formed at the exit of the ion
guide or mass analyser 2 in a similar manner to the
embodiment described above in relation to Fig. 5. The
embodiment shown in Fig. 8 preferably has the advantage that
the amplitude of the modulated RF potential required to
produce a similar amplitude mass dependent pseudo-potential
barrier is less than for the embodiment shown in Fig. 5.
A less preferred method of producing a mass to charge
ratio dependent pseudo-potential barrier within an ion guide
or mass analyser 2 will be described with reference to Figs.
9A and 9B. The ion guide or mass analyser 2 is preferably
similar to the ion guide or mass analyser 2 shown in Fig. 1.
However, the amplitude of the applied RF voltage, or an
additional RF or AC voltage, which is preferably applied to
the ring electrodes 2a is preferably arranged to
progressively increase towards the exit of the ion guide or
mass analyser 2 or along the length of the ion guide or mass
analyser 2. Fig. 9B shows a plot of the maximum amplitude 6
and the minimum amplitude 7 of the additional modulated
voltages as a function of the number of the lens element of
the ion guide or mass analyser 2 as shown in Fig. 9A.
The general fo/m of the additional time varying
potentials V. applied to a lens element n may be described by:
= f(n) cos(ot) (2)
wherein n is the index number of the lens element, f(n) is
the function describing the amplitude of the oscillation for
element n and a is the frequency of modulation.
If the maximum amplitude of an additional modulated
potential described by f(n) increases towards the exit of the
ion guide or mass analyser 2 in a non-linear function as
shown in Fig. 9B, then a mass to charge ratio dependent
pseudo-potential barrier will preferably be formed at the'
exit of the ion guide or mass analyser 2 which is
superimposed over the or any axial pseudo-potential
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corrugations which are foimed as a result of the alternating
phases of AC or RF voltage which are preferably applied to
consecutive ring electrodes 2a.
According to another embodiment one or more mass
selective pseudo-potential barriers may be developed or
created by changing the aspect ratio between the inner
diameter of the ring electrodes 2a and the spacing between
adjacent ring electrodes within or along a specific region or
portion of the ion guide or mass analyser 2. The change in
aspect ratio may be effected by altering the mechanical
design of the ring electrodes 2a and/or by changing the phase
or phase relationship between a series of two or more
neighbouring ring electrodes. For example, if two
neighbouring ring electrodes are switched to be supplied with
the same phase of a modulated potential (as opposed to
opposite phases of modulated potential), then the aspect
ratio in this region or section of the ion guide or mass
analyser 2 will, in effect, also be modified. According'to
one embodiment the polarity or phase of a pair of electrodes
may be switched or reversed so that the effective aspect
ratio of a region'or section of the ion guide or mass
analyser 2 is varied with respect to the aspect ratio as
maintained along the rest of the ion guide or mass analyser
2. The aspect ratio and thus the height of the pseudo-
potential barrier may according to an embodiment be
continuously or otherwise adjusted by continuously or
otherwise adjusting the phase difference between neighbouring
electrodes or groups of electrodes from, for example, 180
degrees to 0 degrees. These methods may be used in
conjunction with the approach of varying the amplitude and/or
the frequency of the applied modulated potential.
Fig. 10 shows an embodiment of the present invention
wherein a preferred ion guide or mass analyser 2 is coupled
in series with a higher resolution mass analyser 11, such as
a quadrupole mass filter. This enables a mass spectrometer
to be provided having an overall improved duty cycle and
sensitivity. Ions from an ion source are preferably
accumulated in an ion trap 8 which is preferably located
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upstream of a preferred ion guide or mass analyser 2. Ions
are then preferably periodically released from the ion trap 8
by pulsing a gate electrode 9 provided at the exit of the ion
trap 8. The ions which are released or pulsed out from the
ion trap 8 are then preferably directed to enter the
preferred ion guide or mass analyser 2. The ions preferably
remain axially confined within the preferred ion guide or
mass analyser 2 due to the presence of a pseudo-potential
barrier formed at the exit of the preferred ion guide or mass
analyser 2. A DC barrier voltage is preferably applied to an
entrance electrode 1 of the preferred ion guide or mass
analyser 2 once ions have entered the preferred ion guide or
mass analyser 2. This preferably prevents ions from exiting
the preferred ion guide or mass analyser 2 upstream via the
aperture in the entrance electrode 1. Once ions have been
accumulated within the preferred ion guide or mass analyser 2
then one or more transient DC voltages or potentials or one
or more transient DC voltage or potential wavefolms are
preferably superimposed on the electrodes forming the ion
guide or mass analyser 2 in order to drive or urge ions
towards the exit of the preferred ion guide or mass analyser
2.
The amplitude of the one or more transient DC voltages
or potentials or the one or more transient DC voltage or
potential wavefolms is preferably progressively increased
with time to a final maximum voltage. Ions are preferably
urged, driven or pushed over the pseudo-potential barrier
which is preferably arranged at the exit of the preferred ion
guide or mass analyser 2 in decreasing order of their mass to
charge ratio. The output of the preferred ion guide or mass
analyser 2 is preferably a function of the mass to charge
ratio of ions and time.
Initially, ions having a relatively high mass to charge
ratio will preferably exit the preferred ion guide or mass
analyser 2. Ions having progressively lower mass to charge
ratios will then preferably subsequently exit the ion guide
or mass analyser 2. Ions having a particular mass to charge
ratio will preferably exit the ion guide or mass analyser 2
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over a relatively short or narrow period of time. According
to an embodiment the mass to charge ratio transmission window
of a scanning quadrupole mass filter/analyser 11 arranged
downstream of the preferred ion guide or mass analyser 2 is
preferably synchronised with the mass to charge ratio of the
ions exiting the ion guide or mass analyser 2. As a result,
the duty cycle of the scanning quadrupole mass analyser 11 is
preferably increased. An ion detector 12 is preferably
arranged downstream of the quadrupole mass analyser 11 to
detect ions.
According to another embodiment the mass to charge ratio
transmission window of the quadrupole mass filter 11 may be
increased in a stepped or other manner which is preferably
substantially synchronised with the mass to charge ratios of
the ions exiting the ion guide or mass analyser 2. According
to this embodiment, the transmission efficiency and the duty
cycle of the quadrupole mass filter 11 may be increased in a
mode of operation wherein only ions having specific masses or
mass to charge ratios are desired to be measured or analysed.
According to another embodiment a preferred ion guide or
mass analyser 2 may be coupled to an orthogonal acceleration
Time of Flight mass analyser 4 as shown in Fig. 11. The
preferred ion guide or mass analyser 2 is preferably coupled
to the Time of Flight mass analyser 14 via a further ion
guide 13. One or more transient DC voltages or potentials or
one or more transient DC voltage or potential waveforms are
preferably applied to the electrodes of the further ion guide
13 in order to transmit ions received from the preferred ion
guide or mass analyser 2 and to transmit the ions in a manner
which preferably maintains the order in which the ions were
received. The ions are therefore preferably onwardly
transmitted to the Time of Flight mass analyser 14 in an
optimal manner. The combination of the preferred ion guide
or mass analyser 2 and the Time of Flight mass analyser 14
preferably results in-an overall mass spectrometer having an
improved dUty cycle and sensitivity. The ions output from
the preferred ion guide or mass analyser 2 at any particular
instance preferably have a well defined mass to charge ratio.
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The further ion guide 13 preferably partitions the ions
emerging or received from the ion guide or mass analyser 2
into a number of discrete packets of ions. Each packet of
ions received by the further ion guide 13 is preferably
trapped within separate axial potential wells which are
preferably continuously translated along the length of the
further ion guide 13. Each axial potential well therefore
preferably comprises ions having a restricted range of mass
to charge ratios. The axial potential wells are preferably
continually transported along the length of the further ion
guide 13 until the ions are released towards or into the
orthogonal acceleration Time of Flight mass analyser 14. An
orthogonal acceleration pulse is preferably synchronised with
the arrival of ions from the further ion guide 13 so as to
maximise the transmission of the ions (which preferably have
a restricted range of mass to charge ratios) present within
each packet or well into the orthogonal acceleration Time of
Flight mass analyser 14.
According to another embodiment a pseudo-potential
barrier may be positioned at the entrance to the preferred
ion guide or mass analyser 2. Accordingly, if ions having a
particular mass to charge ratio have enough initial axial
energy to overcome the pseudo-potential barrier then the ions
will then enter the preferred ion guide or mass analyser 2.
However, if ions having a particular mass to charge ratio
have insufficient initial axial energy to overcome the
pseudo-potential barrier then they are preferably prevented
from entering the ion guide or mass analyser 2 and may be
lost to the system. According to this embodiment the ion
guide or mass analyser 2 may be operated so as to have a low
mass or mass to charge ratio cut off. The characteristics of
the low mass or mass to charge ratio cut off may be altered
or varied as a function of time by increasing or varying the
amplitude of the mass to charge ratio dependent barrier or by
increasing or varying the initial axial energy of the ions
entering the preferred ion guide or mass analyser 2. The
magnitude of the pseudo-potential barrier may be increased by
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increasing the RF voltage and/or by decreasing the frequency
of the RF voltage applied to the electrodes.
Fig. 12 shows a further embodiment wherein the first
annular plate or electrode 15 immediately after or downstream
of the entrance electrode 1 is preferably driven by an RF
voltage supply which is preferably separate or different to
the RF supply which is preferably applied to the other
annular plates or electrodes 2a which preferably foim or
comprise the ion guide or mass analyser 2. When the
amplitude of the RF voltage applied to the first annular
plate or electrode 15 is increased with respect to the
amplitude of the RF voltage applied to the other annular
plates or electrodes 2a then the height of the pseudo-
potential barrier at the entrance of the preferred ion guide
or mass analyser 2 is preferably increased. A similar effect
may be achieved by decreasing the frequency of the RF
modulation applied to the first annular plate or electrode 15
with respect to the frequency of modulation of the potential
applied to the other electrodes 2a of the ion guide or mass
analyser 2.
Fig. 13A shows a plot of the time averaged potential or
pseudo-potential along the central axis of the preferred ion
guide or mass analyser 2 shown in Fig. 12 as experienced by
ions having a mass to charge ratio of 100 when an RF voltage
having a maximum of 100 V at a frequency of 1 MHz was applied
to the annular plates or electrodes 2a. The maximum
amplitude of the modulated potential applied to the first
annular plate or electrode 15 was 400 V. The phase and
frequency of the modulated potential applied to all the
annular plates or electrodes 2a,15 was identical. Fig. 13B
shows the corresponding time averaged potential or pseudo-
potential along the central axis of the ion guide or mass
analyser 2 as experienced by ions having a mass to charge
ratio of 500.
Fig. 14 shows the folm of the radial and axial pseudo-
potential within the preferred ion guide or mass analyser 2
cut along the centre of the z-axis for a region at the
entrance of the preferred ion guide or mass analyser 2 and
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extending from 0 to 1 mm in the x axis (radial direction).
The conditions of voltage and frequency are as previously
described with reference to the embodiment described above
with reference to Fig. 13.
The result of increasing the amplitude of the modulated
potential at the entrance of the ion guide or mass analyser 2
is to produce a pseudo-potential barrier having an amplitude
which is inversely proportional to the mass to charge ratio
of ions. Ions with sufficient axial energy will overcome the
pseudo-potential barrier and will be transmitted into the
preferred ion guide or mass analyser 2 whilst ions with
insufficient axial energy to overcome this barrier will be
lost to the system.
According to an embodiment, the low mass to charge ratio
transmission characteristic may be scanned, varied or stepped
by changing the amplitude and/or the frequency of the
modulated potential applied to the one or more first
electrodes 15 arranged near or at the entrance of the
preferred ion guide or mass analyser 2.
According to another embodiment as shown in Fig. 15, a
preferred ion guide or mass analyser 2 may be coupled to an
ion mobility separator or spectrometer 15a. An ion guide or
mass analyser 2 according to a preferred embodiment may be
positioned downstream of an ion mobility separator or
spectrometer 15a and may be used to prevent the onward
transmission of ions having relatively low charge states
whilst allowing the onward transmission of ions having
, relatively high charge states. If the ion mobility separator
or spectrometer 15a is combined with a mass spectrometer or
mass analyser, then the preferred ion guide or mass analyser
2 may be positioned downstream of the ion mobility separator
or spectrometer 15a and upstream of the mass spectrometer or
mass analyser. The preferred ion guide or mass analyser 2
may be used to prevent the onward transmission of ions having
relatively low charge states whilst allowing the onward
transmission of ions having relatively high charge states for
subsequent mass analysis.
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When used in combination with an ion mobility separator
or spectrometer 15a the magnitude or height of a pseudo-
potential barrier provided in a region of the preferred ion
guide or mass analyser 2 and hence the low mass to charge
ratio cut-off characteristic of the ion guide or mass
analyser 2 may be scanned in synchronism with the pulsing of
ions into the ion mobility separator or spectrometer 15a or
the emergence of ions from the ion mobility separator or
spectrometer 15a. Ions emerging from the ion mobility
separator or spectrometer 15a at a pre-defined drift time and
having a mass or mass to charge ratio below a pre-defined
level may be excluded or prevented from transmission through
the preferred ion guide or mass analyser 2. An important
application of this embodiment is in the discrimination
between ions having the same mass to charge ratio but having
different charge states.
With reference to Fig. 15, ions from an ion source are
preferably accumulated in an ion trap 8. The ions may be
periodically released from the ion trap 8 by pulsing a gate
electrode 9 arranged at an exit of the ion trap 8. The ions
may then be pulsed into the ion mobility separator or
spectrometer 15a. The ions then preferably travel through
the ion mobility separator or spectrometer 15a. The ions are
then preferably temporally separated according to their ion
mobility as they transit through the ion mobility separator
or spectrometer 15a. Ions having a relatively high ion
mobility will preferably exit the ion mobility separator or
spectrometer 15a before ions having a relatively low ion
mobility.
As ions exit the ion mobility separator or spectrometer
15a they are preferably accelerated by maintaining a DC
potential difference between the exit electrode 16 of the ion
mobility separator or spectrometer 15a and the entrance
electrode 17 to the preferred ion guide or mass analyser 2.
Ions entering the preferred ion guide or mass analyser 2 will
preferably experience a pseudo-potential barrier which
preferably has an amplitude which is preferably dependent
upon the mass to charge ratio of ions. Ions having a
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relatively low mass to charge ratio will preferably
experience a pseudo-potential barrier having a relatively
high amplitude whereas ions having a relatively high mass to
charge ratio will preferably experience a pseudo-potential
barrier having a relatively low amplitude. Accordingly, ions
below a certain mass to charge ratio will preferably not be
transmitted into the preferred ion guide or mass analyser 2.
Ions which are onwardly transmitted from the preferred ion
guide or mass analyser 2 are preferably further processed as
required. For example, ions may be transmitted to a mass
spectrometer for subsequent mass analysis. Ions prevented
from entering the preferred ion guide or mass analyser 2 are
preferably lost to the system.
The magnitude of the pseudo-potential barrier provided
within or at the entrance to the preferred ion guide or mass
analyser 2 may be progressively increased during an ion
mobility separation. Fig. 16 shows a plot of mass to charge
ratio value as a function of ion mobility drift time. It can
be seen that singly charged ions and multiply charged ions
separate into two discrete bands. At any given drift time
singly charged ions exiting the ion mobility separator or
spectrometer 15a will have a lower mass to charge ratio than
multiply charged ions exiting the ion mobility separator or
spectrometer 15a at the same time. Accordingly, if the
height of the pseudo-potential barrier at the entrance to the
preferred ion guide or mass analyser 2 is arranged to be
scanned with drift time such that ions with a mass to charge
ratio value less than that indicated by line 18 shown in Fig.
16 are excluded, then predominantly only multiply charged
ions will enter the preferred ion guide or mass analyser 2.
Singly charged ions will preferably be lost. This has the
advantageous result of significantly improving the signal to
noise for the subsequent detection of multiply charged ions.
The ion mobility separator or spectrometer 15a may
comprise a drift tube wherein an axial electric field is
applied or maintained along the length of the drift tube.
The ion mobility separator or spectrometer 15a may
alternatively comprise an ion guide comprising a plurality of
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electrodes having apertures wherein one or more transient DC
voltages or potentials or one or more DC voltage or potential
waveforms are applied to the electrodes of the ion mobility
separator or spectrometer. An AC or RF voltage may be
applied to the electrodes to confine ions to the central axis
= thereby maximising transmission. The preferred operating
pressure for the ion mobility separator or spectrometer 15a
is preferably in the range 10-2 mbar to 102 mbar, more
preferably 10-1- mbar to 101-mbar.
Groups of ions which have been separated according to
their ion mobility are preferably transmitted through the
preferred ion guide or mass analyser 2 without loss of
separation by applying one or more transient DC voltages or
potentials or one or more transient DC voltage or potential
waveforms to the electrodes comprising the ion guide or mass
analyser 2. This is particularly advantageous as the
preferred ion guide or mass analyser 2 is also coupled to an
orthogonal acceleration Time of Flight mass analyser. The
duty cycle may be improved by synchronising the orthogonal
sampling pulse of the mass analyser with the arrival of ions
at the orthogonal acceleration electrode.
Other embodiments are contemplated wherein multiple
pseudo-potential barriers may be generated or created within
or along the length of the preferred ion guide or mass
analyser 2. This enables ion populations trapped within the
preferred ion guide or mass analyser 2 to be manipulated in
more complex ways. For example, the low mass to charge ratio
cut-off characteristic of a first device or region used
during filling of the preferred ion guide or mass analyser 2
may be combined with a different higher low mass to charge
ratio cut-off characteristic of a second device or region
used to allow ejection of ions at the exit of the preferred
ion guide or mass analyser 2. This enables ions to be
trapped within the preferred ion guide or mass analyser 2
with mass to charge ratio values between the two cut-off
values.
Fig. 17 shows an experimental arrangement wherein a
, preferred ion guide or mass analyser 2 was coupled to an
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orthogonal acceleration Time of Flight mass analyser 14. A
continuous beam of ions was introduced from an Electrospray
ionisation source: The ions were arranged to pass through a
first stacked ring ion guide 19 maintained at a pressure of
approximately 10-1 mbar Argon. A transient DC potential
having an amplitude of 2 V was applied to and progressively
translated along the length of the ion guide 19 in order to
urge ions through and along the ion guide 19. Ions
preferably exit the ion guide 19 via an aperture in a DC only
exit plate 20 and enter a preferred stacked ring ion guide or
=
mass analyser 2 maintained at a pressure of approximately 10-2
mbar Argon via an entrance electrode 21. The potential
difference between the exit plate 20 of the ion guide 19 and
the entrance plate 2l of the preferred ion guide or mass
analyser 2 was maintained at -2 V. On exiting the preferred
ion guide or mass analyser 2 ions pass through a transfer
region and are then mass analysed by an orthogonal
acceleration Time of Flight mass analyser 14. The ion guide
19 and the preferred ion guide or mass analyser 2 were both
supplied with an RF voltage of 200 V pk-pk at a frequency of
2 MHz in order to confine ions radially within the upstream
ion guide 19 and the preferred ion guide or mass analyser 2.
In addition to the application of a DC voltage, the
entrance plate 21 to the preferred ion guide or mass analyser
2 was coupled to an independent RF supply having an
independently variable amplitude. The RF supply had a
frequency of 750 MHz. During the experiment the amplitude of
the modulated potential applied to the entrance plate 21 was
increased from 0 V to 550 V pk-pk.
Figs. 18A-18E show mass spectra which were obtained by a
continuous infusion of a mixture of standard compounds
including polyethylene glycol having an average molecular
mass 1000 and Triacetyl¨cyclodextrin wherein [M+H] = 2034.6.
Fig. 18A shows a mass spectrum recorded wherein the
amplitude of the RF voltage applied to the entrance plate 21
was 0 V. Figs. 18B-18E show resulting mass spectra which
= were obtained as the amplitude of the RF voltage applied to
the entrance plate 21 was manually increased from 0 V to a
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maximum of 550 V pk-pk. The mass spectrum shown in Fig. 18E
was obtained when the RF voltage was set at a maximum of 550
V pk-pk. For all the mass spectra the intensity was
normalised to the same value to allow direct comparison.
It can be seen from Figs. 18A-18E that as the amplitude
of the RF voltage applied to the entrance plate 21 was
increased progressively then low mass to charge ratio ions
are increasingly prevented from entering the preferred ion
guide or mass analyser 2 and hence do not appear in the mass
spectra. When the maximum RF amplitude of 550 V pk-pk was
applied as shown in Fig. 18E, then the majority of ions
having mass to charge ratios < 1800 can be seen to have been
removed without there being any attenuation of peaks
corresponding to ions having higher mass to charge ratios.
Applying the RF potential to the entrance plate 21
produces a mass dependent barrier which increases in
magnitude as the amplitude of the RF is increased. At a
particular RF amplitude ions below a certain mass to charge
ratio cannot overcome this pseudo-potential barrier and hence
are prevented from entering the preferred ion guide or mass
analyser 2.
If the frequency of the AC potential applied to elements
of the preferred ion guide or mass analyser 2 which are in
close proximity is different, then there may be some
interaction between the modulated potential forming the mass
selective barrier and the modulated potential used for radial
confinement of ions within the preferred ion guide or mass
analyser 2. This interaction may lead to instability of ions
within these regions of the ion guide or mass analyser 2. In
cases where this interaction is undesirable, regions of
different AC potential may be separated or shielded by
electrodes supplied by DC potentials rather than AC
potentials.
According to the preferred embodiment ions are
preferably pulsed into the preferred ion guide or mass
analyser 2 using a gate electrode. However, alternative
embodiments are contemplated wherein, for example, a pulsed
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ion source such as MALDI ion source may be used and wherein
time To corresponds to the firing of the laser.
According to an embodiment a fragmentation region or
device may be provided after or downstream of the mass
separation region. The potential difference between the
preferred ion guide or mass analyser 2 and the fragmentation
region or device may be ramped down as the amplitude of the
one or more transient DC voltages or potentials or the one or
more transient DC voltage or potential waveforms is
preferably ramped up. The preferred ion guide or mass
analyser 2 may then be optimised for fragmenting a desired
mass to charge ratio range of ions at a given time.
According to the preferred embodiment an electric field,
preferably in the form of one or more transient DC voltages
or potentials or one or more transient DC voltage or
potential waveforms is preferably used to drive ions over or
across a pseudo-potential barrier. According to other
embodiments ions may be driven across a pseudo-potential
barrier by means of the viscous drag caused by a flow of gas.
The viscous drag due to gas flow will become significant for
gas pressures greater than 10-2 mbar, preferably greater than
10-1 mbar. The viscous drag due to gas flow may also be
combined with the force due to an electric field, such as
that derived from one or more transient DC voltages or
potentials or one or more transient DC voltage or potential
waveforms. The forces on an ion due to viscous drag and due
to an electric field may be arranged to work in unison or
alternatively may be arranged to oppose each other.
