Method and device for solid phase microextraction and desorption

A device for carrying out solid phase microextraction is a fiber contained in a syringe. The fiber can be solid or hollow. The syringe has a barrel and a plunger slidable within the barrel, the plunger having a handle extending from one end of the barrel. A hollow needle extends from an end of the barrel opposite to the plunger. The fiber is contained in the needle. When the plunger is depressed, the fiber extends beyond a free end of the needle and when the plunger is in a withdrawn position, the fiber is located within the needle. The syringe protects the fiber from damage. When it is desired to analyze a sample in a bottle having a septum, the needle is inserted through the septum and the plunger is depressed so that the fiber will extend into the sample. After one or two minutes, the plunger is moved to the withdrawn position so that the fiber will return to the needle and the syringe is withdrawn from the sample bottle. The syringe is then inserted through a septum in a gas injection port of a gas chromatograph. The plunger is again depressed so that the fiber will extend into the gas chromatograph and an analysis of the components on the fiber is carried out. Then, the plunger is moved to the withdrawn and the syringe is withdrawn from the injection port. Previously, samples were analyzed using liquid-liquid extraction or using cartridges. Both of these methods are relatively expensive and time consuming. Both of these methods also require the use of solvents which can be difficult and expensive to dispose of.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method and device for solid phase 
microextraction and analysis and, in particular, relates to 
microextraction and analysis being carried out using various types of a 
single fiber which can be coated with various materials or uncoated. 
2. Description of the Prior Art 
Presently, in the organic analysis of environmental samples which involve 
the separation of components of interest from such matrices as soil, 
water, fly ash, tissue or other material, liquid extraction is tradionally 
used as the separation process. For example, water samples are usually 
extracted with organic solvent. Similarly, solid samples are leeched with 
an organic solvent in a SOXHLET apparatus. Methods based on solvent 
extraction are often time consuming, difficult to automate and are very 
expensive since they require high purity organic solvents and these 
organic solvents are expensive to dispose of. Further, the organic solids 
usually have high toxicity and are difficult to work with. In addition, 
the extraction processes can be highly non-selective. Therefore, 
sequential chromatographic techniques must sometimes be used to separate 
complex mixtures after extraction, significantly increasing the overall 
analysis time and the cost. EP-A1-159 230 discloses an extraction method 
of components in a liquid by placing packets of fibers in contact with 
said liquid in extracting the components. 
Solid phase extraction is a known effective alternative to liquid-liquid 
extraction in the analysis aqueous samples. The primary advantage of solid 
phase extraction is the reduced consumption of high purity solvents and 
the resulting reduction in laboratory costs and the costs of solvent 
disposal. Solid phase extraction also reduces the time required to isolate 
the analyte of interest. However, solid phase extraction continues to use 
solvents and often suffer; from high blank values. Further, there is 
considerable variation between the products offered by different 
manufacturers and lot-to-lot variation can be a problem when carrying out 
solid phase extraction procedures. Solid phase extraction cartridges 
available for manufacturers are normally constructed of plastic which can 
adsorb the analyte and increase interferences in the analysis. The 
disposable plastic cartridges used in the solid phase extraction process 
are first activated using organic solvent. The excess organic solvent is 
then removed and the sample to be tested is passed through the cartridge. 
The organic components from the sample are adsorbed on the chemically 
modified silica surface of the material in the cartridge. Both molecules 
of interest as well as interferences are retained on the cartridge 
material. During desorption, a selective solvent is chosen to first remove 
the interferences. The analyte is then washed out of the cartridge. The 
analytical procedure from that point is identical to that used in 
liquid-liquid extraction. The analyte is first preconcentrated and the 
mixture is then injected into an appropriate high resolution 
chromatographic instrument. Steps involving the use of organic solvents 
are the most time consuming. 
SUMMARY OF THE INVENTION 
A device for carrying out solid phase microextraction of components 
contained in a fluid carrier is characterized by, in combination, a fiber 
and a housing surrounding said fiber, said fiber being mounted to a 
movable part in said housing so that said fiber is movable longitudinally 
within said housing. The movable part is movable over a sufficient 
distance to expose a sufficient length of fiber outside of said housing to 
permit microextraction to occur. The movable part is able to successively 
expose a length of fiber outside of said housing to said carrier and 
retract said fiber into said housing out of contact with said carrier. 
A method of carrying out solid phase microextraction and analysis with 
components contained in a carrier uses a fiber. The method is 
characterized by the steps of choosing either the fiber or a coating for 
the fiber based on selectivity of the fiber or coating chosen to at least 
one component in said carrier, contacting said fiber with said carrier 
containing said components for a sufficient period of time for chemical 
extraction to occur with said at least one componet, subsequently removing 
said fiber from said carrier and placing the fiber into a suitable 
analytical instrument and carrying out desorption with respect to at least 
one component on said fiber. 
A method of carrying out solid phase microextraction and analysis with 
components contained in a carrier uses a fiber contained in a housing. The 
housing has access means so that said carrier can be brought into contact 
with said fiber. The method is characterized by contacting said fiber with 
said housing for a sufficient time to allow chemical extraction to occur, 
ending said contact and placing said fiber in a suitable analytical 
instrument in such a manner that desorption occurs with respect to at 
least one component on said fiber.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2 in greater detail, a device 2 for carrying out 
solid phase microextraction has a syringe 4 containing a fiber 6. The 
syringe 4 is made up of a barrel 8 which contains a plunger 10 and is 
slidable within the barrel 8. The plunger 10 has a handle 12 extending 
from one end 14 of the barrel 8. At the opposite end 16 of the barrel 8, 
there is located a needle 18 which is connected to the end 16 by the 
connector 20. The handle 12 and the needle 18 and connector 20 are shown 
in an exploded position relative to the barrel 8 for ease of illustration. 
The fiber 6 is a solid thread-like material that extends from the needle 18 
through the barrel 8 and out the end 14. An end of the fiber 6 (not shown) 
located adjacent to the cap 12 has retention means 22 located thereon so 
that the fiber will move longitudinally as the plunger 10 slides within 
the barrel 8. The retention means can be simply a drop of epoxy which is 
placed on the end of the fiber 6 near the handle 8 and allowed to harden. 
The fiber 6 is partially enclosed in a metal sleeve 24 which surrounds 
that portion of the fiber 6 located within the plunger 10, the barrel 8 
and part of the needle 18. The purpose of the metal sleeve 24 is to 
protect the fiber 6 from damage and to ensure a good seal during operation 
of the device. Extending from the connector 20 is an optional inlet 26. 
The purpose of the inlet 26 is to allow alternate access to the fiber. For 
example, when the fiber is contained within the needle 18, fluid could 
contact the fiber 6 by entering the inlet 26 and exiting from a free end 
28 of the needle 18. The inlet 26 can also be used to contact the fiber 
with an activating solvent. 
In FIG. 2, a schematic version of the device 2 is shown. The plunger is in 
a withdrawn position and the free end of the fiber 6 is located entirely 
within the needle 18. The access permitted by the inlet 26 when the fiber 
is in the position shown in FIG. 2 can readily be understood. Obviously, 
fluid contacting the fiber 6 within the needle 18 could also enter the 
free end 28 of the needle 18 and exit from the access 26. 
In FIG. 3, only the needle portion of the device is shown. A fiber 30 
extending from the metal sleeve 24 is hollow. It can be seen that there is 
an opening 32 in the wall of the metal sleeve 24 to allow access to an 
interior of the sleeve 24 as well as an interior of the fiber 30. For 
example, fluid could enter the inlet 26 and an interior of the needle 18. 
Then, the fluid could pass through the opening 32 and through an interior 
of the fiber 30 and ultimately exit from the free end 28 of the needle 18. 
In this embodiment, the fiber does not extend to the handle 12 (not shown) 
but only the metal sleeve 24 extends to the handle 12. The fiber 30 can 
still be moved beyond the end 28 of the needle 18 by depressing the 
plunger and returned to the position shown in FIG. 3 by moving the plunger 
to the withdrawn position. 
Alternatively, if it is desired to have the fiber 30 located within the 
needle 18 at all times, contact with the fiber 30 can be attained through 
the inlet 26 or the opening 32 and the free end 28. A plug 33 located 
within the metal sleeve 24 prevents any fluid from travelling up the 
sleeve to the handle. In some situations, the fluid could flow through the 
sleeve 24. 
In general terms, the syringe could be said to be a housing for the fibers 
6, 30 and the access means could be the action of the plunger 10 in moving 
the fiber beyond the end 28 or, alternatively, the access means could be 
the inlet 26. 
The disadvantages and inconveniences of the previous processes for 
analyzing various fluids are overcome by the solid phase microextraction 
technique of the present invention. The diameter of the fibers will vary 
but will preferably be between 0.05 millimeters and 1 millimeter. Much of 
the experimentation on which the present invention was based, was carried 
out using fused silica fibers that were chemically modified. The fused 
silica fibers are widely used in optical communication and are often 
referred to as optical fibers. 
Chemical modification of these fibers can be achieved by the preparation of 
the surface involving etching procedures to increase the surface area 
followed by chemical attachment of the desired coating. The stationary 
phases bonded to the surface of the silica fibers are similar to that used 
in fused silica gas chromatograph columns or high performance liquid 
chromatography columns. 
As an example, fused silica fibers were obtained from Polymicro 
Technologies Inc., Phoenix, Ariz. and these fibers were coated with 
polyimide and had an outer diameter of approximately 171 .mu.m. Uncoated 
fused silica was obtained by burning off the polyimide coating and gently 
scraping off the charred portion. To use the polyimide film as a 
stationary phase, it was first heated at 350.degree. C. for four hours. 
The polyimide was then burned off and the char removed, except for a one 
to two millimeter portion at the end of the fiber. In all cases, the 
polyimide was burned off after the fiber had been inserted into the 
syringe and trimmed to the correct length. After burning, the fiber became 
fragile and had to be handled carefully. The metal casing is used to 
strengthen the fiber. The normal lifetime for a prepared fiber was five to 
six weeks with regular use. 
The solid phase microextraction process does not require a sophisticated 
coating system to be a useful technique. Either the uncoated fiber, fused 
silica, silicone or the polyimide films that optical fibers are shipped 
with can be a suitable stationary phase. 
The method of solid phase microextraction and analysis consists of a few 
simple steps. For example, when a water matrix sample containing 
components of interest is desired to be analyzed, the plunger of the 
syringe is depressed and the exposed fiber extending from the free end of 
the needle is inserted into the water matrix sample. The organic 
components of the water are extracted into the non-polar phase. Water is 
considered to be the carrier in a water matrix sample. Where the water 
sample is contained in a bottle containing a septum, the needle is 
inserted through the septum first before the plunger is depressed so that 
the fiber will not be damaged by the septum. When the microextraction has 
occurred to a sufficient degree (usually approximately two minutes), the 
plunger is moved to the withdrawn position causing the fiber to be drawn 
into the needle and the needle is removed from the sample bottle through 
the septum. Preferably, the sample is stirred while the fiber is inserted. 
The time for extraction will depend on many factors including the 
components being extracted as well as the thickness and type of coating, 
if any, on the fiber. Usually, the extraction time is approximately two 
minutes. The plunger is then moved to the withdrawn position to retract 
the fiber into the needle. The needle is then removed from the bottle and 
is inserted through the septum in an injection port of a conventional gas 
chromatograph or other suitable analytical instrument. The plunger is then 
depressed again to expose the fiber and the organic analytes on the fiber 
are thermally desorbed and analyzed. The fiber remains in the analytical 
instrument during the analysis. When the analysis has been completed, the 
plunger is moved to the withdrawn position and the syringe is removed from 
the injection port. Various injection ports are suitable such as the 
"split-splitless" type or the "on-column" type. 
While various types of syringes will be suitable, a HAMILTON 7000 (a trade 
mark) series syringe has been found to be suitable. The syringe 
facilitates convenient operation of the solid phase microextraction 
process and protects the fiber from damage during the introduction into a 
sample bottle or into an injector of an analytical instrument or even 
during storage. The length of the fiber depends on the injector of the 
analytical instrument with which the fiber will be used. Preferably, the 
fiber is mounted in a housing to a movable part so that the fiber is 
movable longitudinally within the housing. Still more preferably, the 
movable part moves a sufficient distance so that at least part of said 
fiber can be extended outside of said housing and retracted into said 
housing successively. The movable part is preferably an elongated member 
which extends partially outside of the housing. The part of the elongated 
member that extends partially outside of the housing preferably has a 
handle thereon. The elongated member can be a plunger. 
In addition to the improved convenience of the present device and method, 
the method differs significantly in the extraction part of the process 
compared to the prior art solid phase extraction process using cartridges. 
The extraction process in accordance with the present invention does not 
require prior sampling of aqueous material since in-vivo or in-vitro 
sampling can be conveniently performed. The microextractor can be directly 
inserted into the fluid stream. The simple geometry of the fiber 
eliminates clogging caused by particle matter present in the samples. 
Also, due to the small size of the fiber, not all of the organic compounds 
are extracted but rather the equilibrium described by the partition 
coefficient between the water and organic stationary phase for a given 
analyte is established. Therefore, the solid phase microextraction method 
of the present invention can be made selective by appropriate choice of a 
specifically designed organic phase. The partitioning between the aqueous 
phase and the organic coating can be described through the distribution 
constant, K: 
##EQU1## 
where C.sub.s is the concentration in the stationary phase and C.sub.aq is 
the concentration in the water. The partition ratio, k', is therefore: 
##EQU2## 
where n.sub.s and n.sub.aq are the number of moles in the stationary and 
aqueous phases, respectively, and V.sub.s and V.sub.aq are the volmaes of 
the respective phases. Rearranging Eqn. 2 yields: 
##EQU3## 
substituting C.sub.aq V.sub.aq for n.sub.aq results in: 
##EQU4## 
where A=KV.sub.s A linear relationship between concentration of analytes 
in aqueous samples and detector response is expected based upon the 
relationship in equation (4). The slope of the linearity curve can be used 
to determine the partition coefficient for a given analyte if the volume 
of the stationary phase is known. Furthermore, the sensitivity of the 
fiber can be adjusted by changing the volume (thickness or area) of the 
stationary phase. 
The linear dynamic range of the method typically extends several orders of 
magnitude for coatings similar to chromatographic stationary phase 
materials. The limit of quantization depends on the partition coefficient 
and the thickness of the coating and can be as low as a few ppT (parts per 
trillion), which was obtained for chlorinated solvents. In this case the 
amount of the solvents extracted by a thick polyimide coating from a water 
sample is about 30 pg per component at a 1 .mu.g/L concentration. This 
amount ensures not only ECD detection but will allow mass spectrometric 
identification and quantization. 
The dynamics of the extraction process is illustrated on FIG. 4 which shows 
an example of a typical relationship between the amount of analyte 
adsorbed onto the microextractor (peak area) versus the extraction time, 
which corresponds to the exposure time of the fiber to the water matrix 
sample. Initially, the amount of analyte adsorbed by the stationary phase 
increases with the increase in extraction time. This trend is continued 
until the point of steady state is achieved which causes the relationship 
to level off. This situation indicates the state of equilibrium between 
the concentration of the analyte in the stationary phase and in the water 
matrix sample and defines optimum extraction time. According to FIG. 3, 
optimum extraction time for uncoated fiber (about 0.1 .mu.m film of silica 
gel) and PCBs as analytes is about one minute. 
FIG. 5 illustrates the chromatogram corresponding to a PCB mixture in water 
extracted and analyzed by the solid phase microextraction method. Peak 
tailing is larger for the more volatile compounds than the heavier, later 
eluting components. This is an effect of thermal focussing that occurs 
when the analytes are volatilized at 300.degree. C. and transferred to a 
150.degree. C. oven. The heavier compounds benefit from thermal focussing, 
but the oven is at too high a temperature to allow focussing of the more 
volatile compounds. The tailing can be alleviated by using a cryogenically 
cooled oven to improve focussing. 
An uncoated fiber can also be used to adsorb benzene, toluene, ethyl 
benzene and xylenes (BTEX) from aqueous solutions. For this separation 
(FIG. 6), a flame ionization detector (FID) was used, illustrating that a 
sufficient quantity was adsorbed for FID detection. This expands the 
general applicability of the fiber as FID detectors are somewhat easier to 
operate and maintain than ECD detectors. The extraction efficiency in this 
case is sufficiently high to deplete significantly the analyte after 2 to 
3 injections if a small volume of aqueous material (1 to 2 mL) is sampled. 
A larger sample volume (100 mL) is thus recommended if multiple injections 
are necessary. 
Moderate levels of organic interferences and variation in ionic strength of 
aqueous solution do not significantly change the extraction equilibria. 
However, large amounts of organic solvent could be added intentionally to 
introduce partitioning selectivity, as is commonly done in liquid 
chromatography. 
The fiber method has great potential for the analysis of highly sorptive 
compounds that can be difficult to sample without loss of analyte. Losses 
to storage bottles and transfer lines could potentially be eliminated by 
sampling in situ and analyzing the fiber in the field using portable gas 
chromatograph instrumentation. The device and method of the present 
invention can utilize a mechanical device such as an autosampler. The 
autosampler can be programmed to operate the plunger at the appropriate 
time to contact the carrier and to insert the syringe and the fiber into 
the injection port of the analytical instrument. The autosampler has an 
advantage over manual extraction and analysis in that the contact time and 
the length of the fiber in the carrier as well as in the instrument can be 
maintained constant. A VARIAN 3500 gas chromatograph and a VARIAN 8100 
autosampler has been found to be suitable. 
Possible applications of this technique include sampling of both surface 
and groundwater samples, either in situ or in the laboratory. It could 
potentially be used in on-line process applications or clinical analysis. 
Both of these applications benefit from the simplified sample preparation. 
The coating can be designed for either a broad scan of the organic 
contaminants (non-selective fiber coating) or selective sampling. This 
method, when combined with laser desorption, could reduce the sample 
extraction and analysis to a fraction of a minute. In this technique the 
optical fiber is used as a light guide. In a variation of the invention, 
the syringe could have a laser source affixed thereto with activation 
means and coupling optics to focus light onto the fiber which will 
transmit the light to a free end thereof to desorb the components thereon. 
Curie point heating and microwave desorption are alternative desorption 
methods. The fiber also shows promise as a method of studying the 
adsorption properties of polymers and for obtaining information about 
partitioning in liquid chromatographic systems. 
FIG. 7 illustrates the advantages of the method of the present invention 
compared to the prior art solvent procedure. The chromatogram from FIG. 7a 
corresponds to silica fiber techniques using C-18 coating and FIG. 7b to 
liquid-liquid extraction with chloroform. In both cases the same effluent 
from a sewage treatment plant was analyzed under the same chromatographic 
conditions. Results are similar, however the total extraction time was 
about an hour for the solvent method and two minutes for the fused silica 
fiber technique. The chromatogram for FIG. 7b shows the presence of the 
solvents used in the liquid-liquid extraction. The solid phase 
microextraction device facilitates easy sampling in the field. In 
addition, when organic solvents are used in the preparation step, the 
corresponding large peak together with possible impurities can mask 
volatile analytes (FIG. 7b). 
In FIG. 8, there is shown a chromatograph for the extraction of gasoline 
components from water using a silicone coated fiber. In FIG. 9, there is 
shown a chromatograph for the extraction of organics from coal 
gasification waste water using a silicone coated fiber. Both analyses and 
identifications for FIGS. 8 and 9 have been done using a mass spectrometry 
detector. 
The device and method of the present invention can also be used for 
extraction and analysis of gases and for supercritical fluids as well. The 
method is not limited to analysis of organic analytes but also for 
inorganic ions by using ion-exchange materials located on the fiber 
surface. In addition to thermal desorption by direct heating, laser 
desorption or conductive heating, for example, microwave desorption or 
Curie point magnetic hysteresis method could be used. Various fibers will 
be suitable depending on the use that is being made of the present 
invention. For example, fused silica, graphite fibers, fibers constructed 
with solid polymeric materials and even metal wires can be used as fibers 
and the fibers can be coated with various materials or uncoated. Some 
suggested coatings are CARBOWAX (a trade mark), octadecyltrichlorosilane, 
polymethylvinylchlorosilane, liquid crystalline polyacrylates, silicone, 
polyimide and grafted self-assembled monolayers. Fibers coated with these 
coatings are stored under nitrogen or helium to prevent absorption of the 
volatile organics present in air. The coatings can be organic or 
inorganic, for example, fused silica surface. 
In addition to having coating located on an outer surface of a solid fiber, 
coating could be located on an inner surface of a hollow fiber. Coating 
could also be located on the packing material used with the fiber. In 
addition to direct extraction, the method of the present application could 
be performed with prior activation using organic solvents by using the 
optional inlet 26 on the syringe. The analytical instrument used with the 
method of the present invention can also be varied. For example, a gas 
chromatograph, a liquid chromatograph or a supercritical fluid 
chromatograph could be used. Other analytical methods such as flow 
injection analysis, mass spectrometry, atomic absorption or emission 
including inductively coupled plasma technique could be used. 
In addition to analyzing for environmental contaminants, the method and 
device of the present invention can be used to monitor or measure the 
components in industrial process streams. The present invention can also 
be used to study properties of coatings, for example, absorption, 
deterioration rates and diffusion coefficients. 
Numerous other variations, within the scope of the attached claims, will be 
readily apparent to those skilled in the art.