Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
133B970
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SAMPLE INJECTOR
BACKGROUND OF THE INVENTION
- This invention relates, in general, to liquid sample
delivery and liquid chromatography and, in particular, to
an apparatus for introducing liquid samples into an
atomic absorption spectrometer.
- It is common practice to use pipetting devices to
~ predetermine the precise volume of a sample to be
analyzed and to use gas pressure, sometimes air pressure,
to dispense the sample from the pipetting device. The
gas pressure may be from a separate tank-type source or
may be provided by a plunger type device. Pipetting
devices are shown in a number of U.S. Patents, for
example, to Morrill, No. 3,200,650 and to Gerrarde, No.
3,040,494 and the textbook of Paul L. Kirk "Quantitative
Ultra Micro Analysis", John Wiley and Sons, New York,
1950, pages 22-26, 73/864.02, teaches pipetting to
determine sample volume. The patents also show a source
of gas to dispense the liquid sample. Plunger type
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dispensing devices, in connection with pipettes, are
shown, for example, in the U.S. Patents to Avakian, No.
3,732,734, to Norton, 3,754,687, and to Parsons,
-`; 4,257,267. The Avakian patent also shows a removable tip
. 5 used with a pipette and the Parson patent shows a
~; removable tip, which is called a pipette, but is not used
- to determine the volume of the liquid sample.
` SUMMARY OF THE INVENTION
This invention comprises a disposable sample tip
- which is used to provide a liquid sample of a
- - predetermined volume and a plunger type injector which is
- used to introduce the sample into a spectrometer with a
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precise amount of air pressure. The sample tip comprises
an outer tube for mounting the sample tip on the injector
and an inner tube (pipette) of a desired bore and
length. The injector is provided with an anti-suction
means so that the sample liquid will not be withdrawn
from the inner tube by the injector in the event the
inner tube is filled with the liquid sample before the
~-: injector is made ready to introduce the sample into the
- : spectrometer.
` It will be apparent to those skilled in the art that,
- while the recommended procedure is to make the injector
ready for the step of introducing the sample into the
spectrometer, either before or after the sample tip is
mounted on the injector, and before the sample tip is
inserted into the liquid to be sampled, it is possible
- that the sample tip will be mounted on the injector and
the sample tip inserted into the liquid to be sampled
before the injector is made ready for the introduction
step. The anti-suction means compensates for this latter
variation from the recommended procedure for if it were
not operative, such a variation would cause all or a
portion of the sample to be withdrawn from the inner
tube.
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It is also to be understood that this compensation
is important since this invention may be used in non-
laboratory environment with relatively unskilled person-
nel.
As will be apparent from the following description
and the drawings, the capillary sample tip is of a pre-
cise internal volume and will only fill to the desired
volume. This feature eliminates the need for an opera-
tor to make a visual determination as to what level the
capillary has been filled and eliminates the need for
removing some of the sample if the capillary is over-
filled. The injector has the ability to deliver a large
blast of air which expels the sample with a high velo-
city to clear the sample tip. More specifically, this
invention involves providing a discrete sample volume
and expelling it with a high velocity blast of air from
a pre-loaded piston which results in the most repeat-
able sample volume when a large number of inexperienced
operators are involved.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of the sample
tip with an internal pipette,
Figure 2 is a plan view showing the sample tip on
the injector,
Figures 3 and 4 show the introduction of the liquid
into the sample tip and how the sample is introduced in-
to the spectrometer,
Figure 5 is an elevational view, in cross-section,
showing the details of the injector with its piston in
an upper or cocked position,
Figure 6 is a view, similar to Figure 5, but show-
ing the piston in its lower or uncocked position,
Figure 7 is an enlarged view of the area encircled
in Figure 5 showing the anti-suction feature of this in-
vention by showing the flow of air through the piston as
the piston is moved upwardly,
Figure 8 is an enlarged view of the area encircled
in Figure 6 showing the piston moving downwardly,
Figure 9 is an enlarged view of the area encircled
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in Figure 5 showing the details of the latch mechanism
in the latched position, and
Figure 10 is an enlarged view of the area encircled
in Figure 6 and showing the latch mechanism in the un-
latched position.
DETAILED DESCRIPTION
The drawings show a sample tip 10 and a plunger
type injector 12. Figure 1 shows the sample tip en-
larged relative to the injector 12 but Figure 2 showsthe relative sizes of the two devices and also shows the
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sample tip 10 mounted on the injector 12.
The sample tip 10 comprises an outer hollow tube 14
and a shorter inner capillary tube (pipette) 16 spaced
from the inner wall 20 of the outer tube 14. Although
shown as one molded piece, effectively one end of the
inner tube 16 extends beyond the outer tube 14 to form an
insertion tip 22 and a step 24 and the other end of the
inner tube 16 terminates substantially midway of the
outer tube 14. The length of the inner tube 16 and the
size of its internal bore establishes the volume of the
sample to be analyzed.
Figure 3 illustrates the step of filling the inner
tube 16 with liquid by inserting the sample tip 10 into a
body of liquid 26 and figure 4 shows the step of
introducing the sample into the spectrometer by inserting
sample tip 10 into a graphite tube 30 of a spectrometer
(not shown) with the step 24 establishing the distance
between the end of the sample tip 10 and the graphite
tube inner surface 32.
` 20 Turning now to figures 5 through 9 which depict the
injector 12, it can be seen that the injector 12
comprises a long tubular body 34 (handle) and a
relatively thin walled hollow nozzle 36 which has a
tubular portion 40 of the same outer diameter as the
tubular body 34, a first taper 42 and, a second tubular
portion 44 of a lesser diameter than tubular portion 40
which terminates in a slightly tapered narrow hollow
point 46. The hollow point 46 holds the sample tip 10 as
shown in figures 5 and 6 and the tubular portion 40 forms
a piston chamber 48. The nozzle 36 is fitted over the
end of the tubular body 34 and held thereon in any
suitable manner as by internal and external complimentary
threads 50.
The tubular body 34 has a central bore 52 in which a
plunger 54 is slidably fit and which extends beyond the
ends of the tubular body 34. The lower end of the
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plunger 54, as more clearly shown in figures 7 and 8, has
a reduced portion 56 which is fitted with a retainer 60
which has a collar 62, a radially extended disc 64 and a
downwardly extending short connecting rod 66. The
.~ 5 retainer 60 is held on the plunger 54 by a lock pin 70
., and lock washer 72 holds a hollow, relatively thin
;~. walled, downwardly opening piston 74 on the connecting
rod 66. Both the piston 74 and the retainer 60 are
.- enclosed in the piston chamber 48 where movement of the
-- 10 piston 74 downwardly will expell a measured amount of air
under pressure from the nozzle point 46 and dispense the
. sample from the sample tip 10.
A counterbore 76 in the lower end of the tubular body
34 encloses a helical piston spring 78 which biases the
piston 74 toward a downward or uncocked position. The
upper end of the counterbore 76 is open to atmosphere by
radial holes 80 (Figs 5 & 6). The spring 78 and the
piston 74 are held in an upper, or cocked, position by a
latching mechanism 82. (See the enlarged view of the
latch mechanism 82 in figures 9 and 10). This latching
mechanism 82 comprises a latch button 84 with an
. extension arm 86 of a lesser diameter and containing an
: opening 90 which allows the plunger 54 to pass
therethrough. The extension arm 86 is disposed in
~ 25 sliding relationship within a sleeve 92 and a blind
radial counterbore 94 in the tubular body 34. In one
position, the cocked position, an edge 96 on the
- extension arm 86 near the opening 90 engages a shoulder
100 on the plunger 54 formed by a reduced radius 102 in
the area of the latch mechanism 82 and, in another
position, the uncocked position, allows the plunger 54 to
move freely in response to the piston spring 78. The
extension arm 86 is spring biased toward the cocked
position by a helical spring 104. As shown in figures
2,5 and 6, a handle 106, attached to the upper end of the
plunger 54, is provided for the purpose of pulling the
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plunger upwardly and is operable manually. Thus, the
latching mechanism 82 will automatically latch the piston
54 in the cocked position when the handle 106 is pulled
-~ upwardly a sufficient distance. The plunger 54 and
piston 74 are released by pressing the latch button 84
~ radially inwardly against the force of the spring 104
which will free the shoulder 100 of the edge 96 and allow
~ the helical spring 78 to move the piston 74 downwardly to
- create a sufficient amount of air under pressure to be
expelled from the nozzle 40 and to expel the sample from
-; the sample tip 10 as shown schematically in figure 4. It
is to be noted that, as shown in figures 5 and 6, the
handle 106 extends into a blind bore 110 in the top of
the tubular body 34 in sliding relationship and the
bottom 112 of the handle 106 engages the bottom 114 of
the blind bore 110 to limit the stroke of the piston 74.
The recommended procedure is to cock the injector 12
; either before and after the sample tip 10 is mounted on
the injector 12 but before the sample tip 10 is inserted
: 20 into the liquid to be sampled.
However, it is possible that an operator will forget
to cock the injector 12 before inserting the sample tip
10 into the liquid and then, realizing his mistake, will
- then cock the injector 12 which normally would withdraw
all or part of the sample into the injector 12.
To prevent this, the injector 12 is provided with an
anti-suction means 120 which is a function of the
retainer 60 and the piston 74 and ~hich will now be
described in detail. This is considered an important
feature of this invention and figures 7 and 6 show its
operation.
It can be seen that the top wall 122 of the piston 74
contains holes 124 (2 shown) of a relatively small size.
These small holes 124 form passage means for air on one
side of the piston 74 to flow to the other side of the
piston 74 and the disc 64 forms a closure means for
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opening and closing these holes 124 during movement of
the piston 74. With the pinning of the retainer 60 to
the plunger 54 by lock pin 70, there is no relative
- movement between the disc 64 and the piston 74, but the
- 5 piston 74, being fixed on the connecting rod 66 by the
lock washer 72 is free to move relative to the disc 64
~ and the distance is determined by the spacing between the
lock washer 72 and the disc 64. With this arrangement,
- when the piston 74 is being pulled to its cocked
; 10 position, the disc 64 is spaced from the top wall 122
allowing air from the upper part of the piston chamber 48
- to flow through the holes 124 downwardly into the lower
part of the piston chamber 48. On the other hand, when
the plunger 54 is released by the latch mechanism 82, the
disc 64 which moves the piston 74 downwardly and, at the
same time, acts as a closure to prevent the flow of air
through the holes 124. At this time, air is free to flow
- through radial holes 80 located at the top of the
counterbore 76. Thus, it can be seen that this
arrangement allows an equilibrium in the air pressure on
both sides of the piston 74 during cocking and also
; prevents the sample in the sample tip 10 from being
~ disturbed by the movement of the piston 74 toward the
-- cocked position.
It is to be understood that wherever the words
- "upper" or "lower", "down" or "up", or "left" or "right"
-- are used, they were used to facilitate the description of
- the invention with reference to the drawings. Also,
while the words "bore" and "counterbore" are used, they
were not meant to imply that these were necessarily
formed by a machining procesQ since the injector (and
many of its parts) and the sample tip may be formed of a
suitable commercially available plastic by a molding
process. It is also to be understood that the liquid of
the sample to be analyzed may be any liquid, but in this
case, lubricating oil is the liquid for which this
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invention is particularly directed so that wear of
movable metal parts, such as aircraft en~ine parts, may
be determined by atomic absorption spectrometry.
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