Note: Descriptions are shown in the official language in which they were submitted.
P ~71016
,
TITLE OF THE INVENTION
A SAMPLE CONTAINER
FIELD OF THE INVENTION
An inert sample container is provided comprising expanded porous
polytetrafluoroethylene for holding an analyte within a matrix that is to undergo
analysis. The conlainer may be employed for general chemical and clinical
10 analyses in toxic~layy or general chemistry purposes; for environmental
c~l'ection such as water analysis soil analysis as well as biological analysis.
BACKGROUND OF THE INVENTION
The storage Iranspo,lc,lion and actual analysis of sample analytes
present sig"ificdnt pr.b'~ms requiring a great deal of time in obta,n;ng a
sample and then pr~pafing it for the appropriate ana ysis. It is desi, dbl~ to
reduce the time and p~padr_~tion necess~ry for such analysis including but not
limited to physical thermal and eAlfaclion analyses. In addition some
analytical techn ~ues require samples to be held within containers during
analysis which require s~hsequent extensive cleaning of the containers after
the analysis has been completed.
As an exa"l~'e U,e~""al deso",Uon analysis requires that samples to be
analyzed be placed directly into stainless steel quartz or glass tubes which
are then placed within a . ha"~ber of the equipment. After the analysis is
complete, these tubes must be thoroughly cleaned so that they may be used
again. This is eAb~",ely cumbersome and ineffective as often a residue is
deposiled on the tube walls after the analyte has been desorbed into the
vapor phase and the matrix of the analyte has been destroyed. Other tubes
may have walls lined with polytetrafluoroethylene (not porous PTFE) but also
require the use of addilional ",alerials such as glass wool to keep particles
contained within the tubes. Such tubes cannot be sealed as purge gas must
be allowed to pass through the sample. There is a need for a simple contain~
to hold the matrix with analyte for analysis and eliminate the need for
extensive cleaning of tubes.
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SUMMARY OF THE INVENTION
An inert sample container is provided comprising expanded porous
polytetrafluoroethylene for holding a matrix with analyte that is to undergo
5 analysis wherein the container has an inlet, walls that form an interior space therein, and at least one sealed end. Preferably the expanded porous
polytetrafluoroethylene has pores with an average size of between 0.1 and
20.0 ~lm in diameter and a porosity of between 10 and 90% and wherein the
analysis may be performed at a temperature of less than 360C. The
10 container may have a tubular or rectangular shape. The container may be
used for many different types of analysis.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a per~pecli~/e view of the tubular container.
Figure 1 a is a longitudinal cross-sectional view of the tubular container.
Figure 1 b is a transverse cross-sectional view of the tubular container.
Figure 2 is a perspective view of a rectangular container of the present
20 invention.
Figure 2a is a longitudinal cross-sectional view of the reclangular
container.
Figure 2b is a transverse cross-sectional view of the rectangular
container.
DETAILED DESCRIPTION OF THE INVENTION
A container for holding a matrix and an analyte for analysis is provided.
The analyte may be in liquid, gas or solid form and the matrix holding the
30 analyte may be soil, plastic, paper, powders, and liquid polymers. The
container is preferably made entirely of expanded polytetrafluoroethylene
thereby causing it to be inert so that the analyte does not becG",e
contaminated by any offgassing from the constituents of the container.
Moreover because the ex~,anded polytetrafluoroethylene is porous, volatile
35 gasses from the analyte are able to diffuse from the container so that both the
vapor portion of the analyte can be analyzed as well as any liquid portion. The
matrix holding the analyte may be degraded during analysis and its residue
remains within the walls of the conlainer.
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The container may be constructed to be sufficiently rigid so that it is
resilient and capable of holding a liquid or other amorphous shape of which
matrix may assume within the container. The resiliency of the container
depends on the ~l,enyll, and thickness of the expanded porous
5 polytetrafluoroethylene used.
The expanded porous polytetrafluoroethylene is made according to the
procedures described in U.S. Patent Nos.4 187 390 and 3 953 566. More
specifically coagulated dispersion polytetrafluoroethylene (PTFE) is lightly
lubricated and extruded as a paste through an annular die extruder. In a
10 series of heating and stretching steps the lubricant is evaporated away and
the PTFE structure is expanded such that the present void space or porosity is
finally between 10 to 95% and is preferably from 70 to 85%. The material is
also heated to above its crystalline melt te",per~lure. A most preferable
porosity for the material is about 70%. The sele~t;on of porosity is ultimately
15 dependent on the prope,lies of the i"ateria:s to be analyzed so that they canbe secured within the container but allow gasses to be ultimately released
during analysis.
The size of the individual pores can also be selected and is dependent
on the properties of the matrix and analyte. Here again the size of the pores
20 is chosen so that vapors of the analyte may be released from the container
while a liquid or solid matrix is held within the container without loss. The size
of the pores may range from 0.1 to 20.0 ~m. in dia,.,eter and is preferably
about 3.5 ~m. The size of the pores and percent porosity can be varied
depending on the different conditions under which the expanded porous PTFE
25 is made.
Similarly the wall thickness of the container may vary depending on the
nature of the materials used for analysis. Generally the wall thickness of the
container is about 1 mm.
The container may be constructed so that it has the necess~ry cross-
30 section to hold the matrix and analyte underya.ng analysis. A preferableconstruction includes a tubular structure as shown in Figures 1 1 a and 1 b
wherein one end of the tube is sealed. This may be accG",p!ished by any
suitable sealing means and may include heat sealing with the use of an
adhesive such as polyethylene or a melt-processible tetrafluoroethylene
35 copolymer fc awod by heat and/or co",pr~ssion or simple fusion bonding of
the walls. Ultrasonic welding may also be used. Other l-letllods of sealing the
end of the container may be accomplished by knotting or crimping. The other
end of the container serves as an inlet for the ",alerisls that undergo analysis
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which can also be subsequently sealed or capped off with a plug of
polytetrafluoroethylene or glass wool. Altematively the inlet may be sealed
shut after the matrix and analyte have been added wherein the sealing is
accomplished by any of the means identified above. A third altemative is that
5 the inlet of the container is not sealed or plugged at all but left open.
Although the preferable shape of the container is tubular, there are no
limitations on the shape. Thus the container may also be rectangular, square,
or have some other shape as shown in Figures 2, 2a, and 2b. Any walls of the
container may be sealed together by any of the means described above.
In practice, several tubular containers made of expanded porous
polytetrafluoroethylene were used for holding matrices consisting of
contaminated soil that were to undergo themmal desG",tion analysis. The
containers had a porosity of about 70%, pore size of about 3.5 ~m. in diameter
and had inner diameters of 3mm and outer dia",e~era of 4mm. The empty
containers were first preweighed and then filled with the matrix containing the
analyte and reweighed. Some containers did not have the second end sealed.
Other containers had both ends sealed. Each filled container was then
slipped into a thermal desorption stainless steel tube and placed within the
analytical chamber of the test machine (in this case - Perkin Elmer Model
ATD400). The machine was then oper~ted in accor~ance with standard
operating procedures established by the manufadurer of the analytical
equipment. The equipment ran at about 200C with no conta",inating
inte, rerence from any of the tubular containers. Data of the analyte was
obtained from the mass spedo",eter readout. After analysis was complete,
the stainless steel tubes were removed from the cha",ber and the expanded
porous PTFE tubular containers with the residual matrix of soil were easily
removed from the stainless steel tubes and .lis~,ded. Although not required,
the stainless steel tubes were cleaned for the next analysis.
AltemaUvely, the containers were used to hold ",onoi"ers and o'.gomera
that were analyzed according to the procedures described above. Here the
containers were particularly useful as the ",ono")e,a and oligomers were
extremely messy and viscous. If stainless steel tubes had been used by
themselves, subalan~ial cleaning of the stainless steel tubes after use due to
the heavy residual buildup would have been required.
Although the procedures described above require that the containers be
used in a test environmént of about 200C, the containers are suitable for use
in env;,unn,enta up to about 325C for 5 minutes without any difficulty.
Expanded porous PTFE containers may easily be removed from stainless
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steel tubes at this temperature after use. At higher temperatures (in the range
from 335C to 355C) the containers do not deteriorate but forceps or other
gripping means are required to remove the container from the tube. The
container made solely of expanded porous polytetrafluoroethylene should not
be used in temperatures above about 360C due to thermal degradation.
The containers are also believed to be particularly useful in supercritical
fluid exl,a- lion wherein a matrix with analyte may be contained within the
expanded porous polytetrafluoroethylene container which is then exposed to
liquid carbon dioxide. The solutes may be exl,dcled for further analysis
carbon dioxide gas may be released and the container remains with the
residual matrix.
As used herein:
Pore size for the material used in the container was determined by the
amount of air pressure required to force liquid from the largest wetted pore of
a membrane. A bubble point rating is used to determine when the largest pore
yield a bubble; the larger the pore the less pressure required to form the
bubble. ASTM:F31~80 was used to determine this parameter.
Porosity (% void space) was determined by density (weight per volume
measurei"enls).
Wall thickness was determined by calculating the difference between the
measured outer dia,~,eter of the tubular container and the measured inner
clia"~eter.
