Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF T~E IN~7ENTION
This invention relates to a method and apparatus for controlled delivery
of a particulate material and particularly for controlled volumetric delivery of a
particulate sample for analysis.
S BACKGROUND OF THE INVENTION
With the advent of high temperature excitation sources for analysis by
optical atomic emission spectrometric methods, for example, Inductively
Coupled Plasma Atomic Emission Spectrometry (ICP-AES), there has been a
growing interest in the direct analysis of solids. This approach would bypass
the tedious, time consuming and error-prone sample dissolution step involved
in conventional analytical systems. However, the development of a practical
method to introduce solids in a manner suitable for analytical purposes has
been impeded by several major technological problems. The sample must be
introduced uniformly so that the variations of the plasma charactelistics are
minimal. It is desirable to have a uniform sample delivery to satisfy the
requirements of data acquisition techniques incorporated with most of the
commercially available spectrometers. A controlled delivery of the sample is
important to avoid overloading of the atomization source. It would be
desirable to introduce a known amount of material within a desired time
period. For a representative analysis the system should be able to introduce
particles of a wide range of sizes and matrices without segregation according tosize or density. Also, most systems require that the sample be transported in
an inert gas.
There are several possible approaches to analyze solid materials without
acid digestion, dissolution or other chemical processing to yield a liquid sample.
Methods based on solid/liquid slurry nebulization, electrothermal vaporization,
laser ablation, direct sample insertion have been proposed for analysis of
solids. Methods based on the introduction of powders by the formation of a
fluidized beds and aerosols has ~Iso been proposed to meet some of the
analytical requirements.
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A limitation of most of the systems previously described is that the
analytical signals resulting from the introduction of the solid sample is
transient; the mass of solid and the time duration of sample delivery is poorly
controlled, or not controlled at all (eg. laser ablation).
In U.S. patent 4,836,039 the present inventors have disclosed a method
to generate a substantially uniform flow of particles by making use of a
combination of mechanical agitation of the container and a flow of a gas for
the generation of a fluidized bed.
However, none of the present systems provide all the features desired
for solid sample delivery. Specifically, it would be desirable to be ab]e to
deliver a known mass of material within a known period of time, and to
provide a constant feeding rate from the beginning to end of the sampling
period. Furthermore, it would be desirable to be able to provide controlled
delivery by electronic means under computer control to obtain a predetermined
sample delivery rate, predetermined sampling intervals, etc.
~UMM~RY OF T~IE I~VENTION
An object of the present invention is to provide controlled volumetric
delivery of particulate material.
Another object is to provide a system that facilitates delivery of
particulate material at a constant volumetric rate.
Another object is to provide a system that facilitates delivery of
particulate material at a substantially constant volumetric rate independent of
other operating parameters such as gas pressure or gas flow rates.
Another object is to provide a system that facilitates the use of
removable sample containers for sample changing.
Yet another object is to provide a system that facilitates total
consumption of the sample from the sarnple container.
The present invention provides an apparatus for controlled volumetric
delivery of particulate material, comprising; an elongated container for
receiving particulate material to be delivered; a tubular member having a
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sample receiving inlet for insertion into the container, and an owtlet;
traversing means for traversing the container relative to the tubular member
along a common longitudinal axis at a predetermined rate selected to obtain
the desired volumetric sample delivery rate; fluidizing means comprising means
S for agitating a surface portion of the particulate material within the container
while the container is traversed relative to the tubular member; an enclosure
for enclosing a region including the opening of the container and the sample
receiving inlet of the tubular member; and inlet means communicating with the
enclosure for receiving a transporting gas for transporting fluidized particulate
material from the container.
BRIEF DESCRIPTION OF TEIE DRA~ NGS
Fig. 1 is a schematic representation of one embodiment of the present
invention.
Fig. 2 shows details of a portion of the apparatus of Fig. 1 in
preparation for, and prior to, sample delivery.
Fig. 3 shows details of a portion of the apparatus of Fig. 1 in operation
for sample delivery.
Fig. 4 is a schematic representation of another embodiment of the
present invention.
DE~CRIPTION OF T~E Pl~EFERRED EMBODIMENT~
With reference to Figs. 1 to 3, the present invention comprises an
elongated container 1 for receiving particulate material 2 to be delivered, a
tubular delivery member 3 for insertion into the container 1, and vibrating
means 16 for fluidizing a surface portion of the sample in the container 1.
The container 1 will preferably be removably supported by a suitable
supporting member S shown as including a container receiving recess 6. The
container supporting member 5 is shown to be movable Yertically between the
positions Sa and S by suitable traversing means 7. In the position (S), as shownin Fig. 1, the supporting member S is in sealing engagement with the opening 8
of the enclosure 13 with the use of a suitable seal 9. For delivery, as will be
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described, the traversing means 7 is adapted to move the supporting member 5
further upward at a predetermined rate, from the position (5) shown, to allow
the receiving inlet 4 to reach the bottom of the container 1. The traversing
means 7, in a lower position 7a, allows removal of a container for sample
changing.
The traversing means 7, for the purpose of sample delivery, is selected
to provide relative linear motion between the sample receiving inlet and
particulate material at a predetermined rate. The traversing means should
provide relative motion in a positive and quantifiable manner so that motion is
independent of other uncontrolled parameters, such as gas pressure, physical
properties of the sample, friction, etc. Suitable traversing means rnay include a
mechanical mechanism or an electrical device such as a stepper motor.
The enclosure 13 includes inlet 10 for supplying a transporting gas for
transporting particulate material fluidized by the agitating tubular member 3
from the container.
The preferred application of the present invention is for delivery of a
particulate sample to an analyzing device (not shown). For this purpose the
outlet 11 of the tubular member 3 may communicate with a flow combining
portion 12 where flow from outlet 11, which includes entrained particles from
container 1, is combined with a carrier gas supplied at inlet 14.
To begin operation the container la is filled with the particulate sample,
and the tube is fitted into the recess 6a of the container supporting member
Sa. The traversing means 7 is moved ~rom position 7a to 7 to bring the sample
toward the tip 4 of the tubular member 3. Transporting gas is supplied to inlet
10. The directions of the gas flows before the container supporting member 5
reaches the seal 9 are shown in Fig. 2. A portion of the gas flow entering inlet14 exits the flow combining portion 12 through the outlet 11 of tubular
member 3 and then through the unfilled portion of the container 1 to the
atmosphere. This ensures that any remaining air inside the container will be
purged before the container supporting member 5 reaches the seal 9. The gas
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flow entering inlet 10 escapes through the opening 8 in enclosure 13 and
prevents contamination of enclosure 13 with air.
The relative positioning of the inlet end 4 of the tubular member 3, seal
9, the upper end of the container supporting member 5, and the position of the
sample is arranged such that the tubular member 3 does not reach the sample
2 until the container supporting member S is in sealing engagement with the
opening 8 of enclosure 13 as shown in Fig. 3.
In operation, sample delivery is initiated by relative placement of the
inlet end 4 of the tubular member 3 into proximity with the sample. In the
embodiment shown in Fig. 1, the traversing means 7 is used to move the
supporting member S and sample container 1 upward into contact with the
inlet end 4 of the tubular member 3. The sample at the surface of the sample
is fluidized by the motion of the tubular member 3, and carried to the sample
analyzing device through the tubular member 3 due to high linear velocity of
the gas as shown in Fig. 3. The agitation of the sample provides uniform
fluidization of particles on the surface and reduces abrupt changes in
entrainment of the sample through the tubular member 3. As delivery
proceeds, only the surface portion of the sample is fluidized, and therefore
segregation of particles due to variations in size and mass is avoided.
However, when begiIming and ending delivery it is possible that some
segregation of particles can occur.
The delivery rate of the sample is controlled by the rate that the inlet
end 4 of the tubular member is inserted into the sample 2 by traversing means
7. Delivery of the sample can readily be started and stopped by starting and
stopping the traversing means 7, for example, with suitable electrical control
means.
It should be noted that sample delivery can be stopped and started at
any time without any alteration to the gas flows entering at inlets 10 or 14. Inthis way the gas flow rate to the analyzing device does not alter during changesin sample delivery rate. Furthermore, the flow rates of gas, and the gas
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pressure within chamber 12 and 13 can be allowed to stabilize before any
sample is carried to the analyzing device. The above is important for
application of the present invention to chemical analysis of samples using
analyzing devices based on plasmas or flames.
The rate of transporting gas flow supplied to inlet 10 is selected to
provide efficient transport of the sample through the tubular member, and in
particular, must be sufficient to provide removal of all the sample that is
fluidized in the container. A carrier gas may be supplied to flow combining
portion 12 at inlet 14 to provide a make-up gas to match the requirement of
the analyzing device.
The flow combining portion 12 will preferably define an annulus around
the outlet 11 of the tubular member such that gas flow to the analyzing device
(not shown) via conduits 15 will exit in the form of a sheath or spiral flow to
maintain the sample particles at the centre of the gas stream. This will reduce
the deposition of particles along the walls which can cause carry over from one
sample to the other. The net gas flow entering to the analyzing device will be
the sum of the two flows provided at inlets 10 and 14.
It should be noted that the delivery rate of sample is essentially
independent of the gas flow rates or gas pressure supplied at inlets 10 and 14.
Sample delivery rate is determined by the linear motion of the h~bular member
3 inlet relative to the sample container 1, ~hich is controlled by the traversing
means 7. Specifically, the volumetric delivery rate is the product of the cross-sectional area ~imes the linear velocity of the tubular member 3 relative to thesample container 1.
Preferably the cross-sectional area will be uniform so that delivery rate
is dependent only on the linear motion of the tubular member relative to the
sample container 1. For most applications it will be desirable that delivery rate
be constant which is achieved by arranging that the linear velocity of the
tubular member relative to the sample container 1 is constant. Hence, by
moving the sample container 1 upwardly at a constant rate until its bottom
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reaches the inlet tip 4, provides that the total sample material is introduced at
essentially the same feeding rate throughout. The constant relative velocity
also facilitates achieving steady state operation.
For quantitative analysis requiring total consumption of a measured
S sample, the components will be arranged to allow the inlet tip 4 to reach the
bottom of the container 1, which will be provided with a suitable geometry to
facilitate egress of all material.
Various means may be used for fluidizing the surface layer of sample 2.
In an embodiment such as illustrated in Fig. t, suitable means for agitating thesample can include an ultrasonic or electromagnetic transducer 16 that vibrates
the sample receiving inlet 4 of the tubular member 3. Fluidization can be
effected by various agitation means that provides relative motion between the
inlet 4 of the tubular member 3 and container 1. For example, either, or both,
of the tubular member or the container can be vibrated, rotated, or otherwise
moved relative to the other. The amount of agitation requ;red for fluidization
of the sample will vary dependin~ on the physical properties, such as size,
density, and/or electrostatic properties of the sample particles. For example,
for certain materials the sample may be fluidized sufficiently by the flow of
transporting gas alone. For material having dense or large particles additional
agitating means such as shown in Fig. 1 may be required.
Fig. 4 shows an embodiment for fluidizing the sample by rotating the
container 21 which is removably attached by retaining means 32 to rotatable
means 26.
As in the embodiment of Figs. 1 to 3, removability of container
facilitates exchange of samples. In addition, since a new sample is in a new
container, carry-over from a previous sample is minimized.
Unlike the embodiment oE Figs. 1 to 3 the tubular mernber 23 is
stationary while the rotation of the container 21 provides the relative motion
between the container 21 and tubular member 23.
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In Fig. 4 the container supporting means includes the container
retaining member 32, disposed on rotating means 26, and the sleeve portion 30
attached to the enclosure 29.
In a manner similar to that of the embodiment of Figs. 1 to 3, a
S transporting gas can be supplied at inlet 20 for transporting material from the
container 21. A carrier gas may be supplied at inlet 24 of combining chamber
22 to further carry the material to an analyzing device (not shown) via conduit
25. Alternatively, the transporting gas can be supplied via inlet 31 in
enclosure 29 which communicates with enclosure 28 via the sleeve portion 30.
The lower enclosure 29 may be provided with an inlet 31 for receiving a
small quantity of inert gas to avoid contamination of enclosure 29 with air
while sleeve portion 30 is disengaged from opening 33 of enclosure 28. At
other times the inlet 31 can be closed, or, as indicated above may also be used
to provide the transporting gas for transporting the fluidized sample from the
container 21.
As in the embodiment of Fig. 1, the delivery rate of the sample is a
function of the rate that the inlet end of the tubular member 23 is inserted
into the sample by traversing means 27.
It should be noted that in both embodiments described above, the same
traversing means is used to provide the two functions of providing the relative
motion between the inlet end of the tubular member and the sample, and also
for moving the container supporting means and enclosure opening means
relative to one another sealing and for sample changing. It will be understood
that these two functions could be provided by separate means. For example, in
an alternative arrangement the traversing means 27 shown in Fig. 4 could be
located inside the enclosure 29, in whlch case other separate traversing means
would be used to engage and disengage member 30 from enclosure 28. Also,
in another embodiment of the invention the traversing means and fluidizing
means could be provided by the same device.
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