Abstract:
A device for extracting an analyte from a sample matrix comprises a sorption vial with a conically shaped interior surface, which is coated with a sorbent material. A method for extracting an analyte from a sample matrix includes retaining the sorption vial within a sample vessel with the sorbent coating exposed to the sample matrix contained in the sample vessel. After the analyte is collected in the sorbent material, the sorption vial may be removed from the sample vessel and sealed, or a small amount of elution solvent may be added to the sorption vial before sealing. The sorption vial containing the analyte may then be stored or transported to a lab for further analysis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the extraction and collection of one or more analytes by a sorption process. Specifically, this invention relates to a device and method for performing direct vial extraction. 
     2. Description of the Related Art 
     To prepare samples for chemical analysis, often analytes, or the compound of interest, must be separated from a sample matrix, such as water, soil or animal tissue and presented in a form suitable for a particular piece of analytical equipment, such as a gas or liquid chromatograph. There are various extraction methods known and used to collect and prepare samples for such chemical analysis. These methods include liquid/liquid extraction, solid phase extraction, solid phase microextraction and stir-bar sorptive extraction. The trend in the industry is toward simplified sample preparation that results in pollution prevention and waste minimization. 
     Liquid/liquid extraction partitions an analyte between two immiscible phases, such as an organic solvent and an aqueous phase. When an aqueous phase contains the analyte it is extracted into the immiscible organic solvent by placing the two phases into contact. Extraction is enhanced by mixing. A relatively large volume of solvent (typically greater than 100 mL) is necessary to carry out the extraction. Partitioning of a compound between the solution solvent and extractant solvent is governed by the distribution constant, K, and the phase ratio, r (The ratio of the quantity of the solvent to that of the other phase). An example of such an extraction would be EPA test method SW846 3510 which specifies that one liter of aqueous sample should be serially extracted with 350 mL of methylene chloride. When the entire procedure is considered, a total of 500 mL of solvent is used for each sample. The solvent extract must be evaporated to reduce its volume to between 1 and 2 mL for placement into an autosampler vial prior to analysis. 
     Solid phase extraction (SPE) is often used to extract a sample prior to analysis by chromatography. SPE uses silica particles with an organic layer covalently attached to the surface of the particles. The silica particles are packed into a tube or disc, such as a polyethylene syringe barrel. The sample is then prepared and an analyte extracted by passing the sample through the solid sorbent. The analyte is then desorbed from the SPE media by solvent extraction. An example of such an extraction is EPA test method SW846 3535 which utilizes one liter of sample but requires approximately 50 mL of solvents. The solvent extract must be evaporated to reduce its volume to between 1 and 2 mL for placement into an autosampler vial prior to analysis. 
     It is known in the art to use a sorbent to extract an analyte from a solution. The analyte is later extracted from the sorbent by thermal desorption or by back extracting with a small amount of organic solvent. Sorption materials are usually homogenous, non-porous materials that are above their glass transition point (T g ) and in which the analyte can dissolve. The sample may be removed for analysis by thermal desorption or solvent extraction. 
     Solid phase microextraction (SPME) is an extraction technique wherein a fiber is coated with a sorbent layer. The coating may be a polysiloxane or other immobilized sorbent. The fiber is immersed in a liquid or exposed to its headspace during which time the analyte is retained. The fiber may then be inserted into a gas chromatograph injection port for analysis where it is thermally desorbed or may be back extracted with a suitable solvent. SPME is not accepted for EPA test methods. 
     Stir-bar sorptive extraction (SBSE) is used primarily for direct mode sampling. SBSE utilizes a thick sorbent coating on a magnetic bar stirrer that stirs the sample for a predetermined amount of time during which time the analyte partitions between the stir-bar sorbent and the sample. After extraction, the stir-bar is removed and the analyte is thermally desorbed to the injection port of a gas chromatograph. 
     Examples of the prior art follow: 
     U.S. Pat. No. 5,595,653 issued to Good et al. on Jan. 21, 1997 discloses an apparatus for extracting an analyte from a liquid sample. The apparatus comprises a microcolumn having a microparticulate media sandwiched between two compression layers. The compression layers are preferably a binder-free glass fiber, held in the microcolumn by upper and lower polypropylene mesh. 
     U.S. Pat. No. 5,635,060 issued to Hagen et al. on Jun. 3, 1997 discloses a solid phase extraction or chromatographic medium. The medium comprises a porous nonwoven fibrous matrix comprising at least one of polytetrafluoroethylene and blown microfibers, and sorptive or reactive hydrophobic siliceous molecular sieve particulates enmeshed in the matrix. 
     U.S. Pat. No. 5,911,883 issued to Anderson on Jun. 15, 1999 discloses a solid phase extraction article having a porous, particle loaded, fibrous sheet material spiral-wrapped around its axis is provided. The sheet material is wound around itself to provide multiple layers of sheet material, each layer of sheet material being spaced from each adjacent layer of sheet material. 
     U.S. Pat. No. 5,897,779 issued to Wisted et al. on Apr. 27, 1999 discloses a cartridge device for removing an analyte from a fluid. The cartridge comprises a hollow core, a sheet composite comprising a particulate-loaded porous membrane and, optionally, at least one reinforcing spacer sheet. The particulate is capable of binding the analyte and the sheet composite is formed into a spiral configuration about the core. 
     U.S. Pat. Nos. 5,415,779 and 5,595,649 both issued to Markell et al. on May 16, 1995 and Jan. 21, 1997, respectively, disclose a particle loaded, porous, fibrous compressed or fused article for separations and purifications. The article comprises a nonwoven fibrous polymeric web, which preferably is thermoplastic, melt-extrudable, and pressure-fusible blown microfibrous web, and sorptive particles enmeshed in the web. 
     U.S. Pat. No. 5,472,600 issued to Ellefson et al. on Dec. 5, 1995 discloses a gradient density filter made from sheets of blown polypropylene microfibers where the microfibers of at least one of the sheets have an effective fiber diameter less than that of the other sheets. 
     U.S. Pat. No. 5,403,489 issued to Hagen et al. on Apr. 4, 1995 discloses a method and apparatus for performing solid phase extraction (SPE) on a fluid that contains solubles and suspended solids. The apparatus includes a conduit, a SPE medium located in the conduit, and a fluid flow direction altering mechanism or a SPE rotating mechanism. 
     U.S. Pat. No. 5,391,298 issued to Pieper et al. on Feb. 21, 1995 discloses an apparatus that can be used to perform a solid phase extraction under pressurized conditions. The apparatus includes a pressurizable housing with an inlet tube that can communicate with a pump, which feeds a liquid to the housing under positive pressure. A disk assembly includes fluid-permeable, porous sheets on opposite sides of an SPE membrane. 
     U.S. Pat. No. 5,279,742 issued to Markel et al. on Jan. 18, 1994, reissued as U.S. Pat. No. Re. 36,811 on Aug. 8, 2000 discloses a method for isolating an environmentally hazardous organic contaminant from a fluid utilizing a solid phase extraction medium. The medium comprises a PTFE fibril matrix, and sorptive particles enmeshed in the matrix. The separations can be efficiently performed in a stacked disk format. 
     U.S. Pat. No. 5,691,206, issued to Pawliszyn on Nov. 25, 1997 discloses a device for carrying out solid phase microextraction. The device is a fiber, solid or hollow, contained in a syringe. The syringe has a barrel, a plunger slidable within the barrel and a hollow needle extending from the end of the barrel opposite the plunger. The needle contains the fiber. 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. To collect a sample, the needle is inserted through a septum in a bottle containing the sample and the fiber is extended into the sample. After a predetermined amount of time, the fiber is returned to the needle and the syringe is withdrawn from the bottle. The sample is analyzed by inserting the needle through a septum in a gas injection port of a gas chromatograph and extending the fiber. 
     U.S. Pat. No. 5,565,622, issued to Murphy on Oct. 15, 1996 discloses a simplified method for solid phase extraction of components of interest from a sample. A syringe is used in which the inner surface of the cannula or needle is at least partially coated with a stationary phase such that aspirating the sample into the needle results in adsorption of the components of interest into the stationary phase. Aspiration of a solvent may be employed for removing the components of interest from the stationary phase for direct injection into a chromatographic instrument, or the components of interest may be removed by thermal desorption, wherein the needle is placed in the injection port of the chromatographic instrument and heated. 
     U.S. Pat. Application Pub. No. US 2002/0105923, applied for by Malik, published on Oct. 17, 2002 discloses a method of preconcentrating trace analytes by extracting polar and non-polar analytes through a sol-gel coating. The sol-gel coating is either disposed on the inner surface of the capillary tube or disposed within the tube as a monolithic bed. 
     It would be an improvement to the art to have a device in which the extraction may be performed and the analyte conveniently and transportably stored for later analysis. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention comprises a device and method for performing direct vial extraction. 
     Accordingly, the objects of my invention are to provide, inter alia, a single step solid phase extraction system that:
         minimizes the amount of solvent used;   minimizes the amount of labor required to perform an extraction;   minimizes glassware;   allows samples to be archived;   allows extraction to be performed at the sampling site rather than the laboratory;   allows the extract to be subjected to replicate analysis;   allows the use of gas or liquid chromatography autosamplers;   allows the use of disposable sample vials;   has greater reproducibility than solid phase micro extraction;   reduces or eliminates sample cross contamination; and   does not require expensive thermal desorption equipment.       

     This invention is a sorption vial that can be used for the extraction of a sample, or analyte, from a sample matrix and a method of using the sorption vial to perform the extraction. Preferably, the sorption vial has a conically-shaped interior bottom surface coated with sorptive material. An adapter may retain the sorption vial in a fixed position within a larger sample vessel such that the sorptive coating is exposed to a sample or its headspace. After partitioning of the sample in to the sorptive material, the sorption vial may be removed from the sample vessel. An elution solvent is used to extract the analytes from the sorptive coating, which is then sealed and transported to a location for further testing. Alternatively, the sorption vial may be used directly to receive the sample and perform the extraction without using the larger sample vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a sample vessel with a sorption vial. 
         FIG. 2  is a perspective view of the preferred embodiment of a sorption vial. 
         FIG. 3  is a cross-sectional view of a sorption vial with a vial cap. 
         FIG. 4  is a perspective view of an alternative embodiment of a sorption vial. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , the preferred embodiment of the surface sorbent micro extraction (SSME) assembly is depicted as  10 . SSME assembly  10  comprises a sorption vial  20  and a sample vessel  30 . 
     Referring to  FIGS. 1 and 2 , sorption vial  20  is made from a rigid, nonreactive material, such as silica glass. In the preferred embodiment, sorption vial  20  has a cylindrically-shaped interior wall  21  with a conically-shaped bottom surface  22 . Sorption vial  20  also has a vial base  40  and a vial neck  26  through which there is an opening  23  to interior surface  22 . Bottom surface  22  is oriented such that the vertex  24  of the conical bottom surface  22  is proximate vial base  40  while the directrix  42  is contiguous with interior wall  21 . 
     An alternative embodiment of sorption vial  20  is shown in  FIG. 4  as sorption vial  200 . Interior wall  222  is conically shaped. Alternative interior wall  222  is oriented such that the vertex  224  of the conical interior wall  222  is proximate vial base  240  while the directrix  242  is proximate vial neck  226 . 
     It is known in the art that vials need a means for closure. It is also known in the art that autosampers require a means by which they may grasp the vial. Referring to  FIGS. 2 and 3 , vial neck  26  is an example of a means known in the art by which vials may be sealed and provide a shape suitable to autosamplers. In this example vial neck is formed such that a vial cap  28  may be placed over opening  23  to seal sorption vial  20  after a sample  15  (shown in  FIG. 1 ) containing the analyte to be extracted is exposed to interior surface  22 . Vial cap  28  may be any type of cap including a screw-on cap, a crimp cap, or a plug, so long as vial cap  28  is leak-proof. 
     A sorptive coating  27  is applied proximate the vertex  24  of interior surface  22 . When interior surface  22  is cylindrical rather than conical, sorptive coating  27  may be applied on the cylinder interior wall or the flat or conical bottom surface or both. 
     In the preferred embodiment, the sorptive coating  27  is a hydrophobic coating, such as an immobilized polysiloxane, for example polydimethylsiloxane (PDMS), which contains only methyl functional groups. The name “siloxane” is based on the Si—O—Si unit and has found acceptance in scientific nomenclature. Polysiloxanes are polymers with repeating siloxane units. Each repeating siloxane unit contains two functional groups attached (e.g. dimethyl) which may, or may not, be of the same type of functional group. A functional group is an atom or combination of atoms which gives a polymer its distinctive and characteristic chemistry. A polysiloxane of 50 repeating units would therefore have 100 methyl groups, whereas a siloxane unit with two different types of groups such as phenymethyl would have 50 of each “type” in the polysiloxane. 
     It is known in the art that immobilized polysiloxanes that contain other types of functional groups, may be used as sorbents. These include immobilized polysiloxanes containing phenyl or trifluoropropyl functional groups. Examples of these polysiloxanes include diphenylsiloxane-dimethylsiloxane copolymers and trifluoropropylmethylsiloxanes. For more selective sorption applications the immobilized polysiloxane may contain other types of functional groups including alkyl, alkenyl, alkynyl, aryl, alkylaryl, alkenylaryl, alkynylaryl, haloalkyl or haloaryl. A polysiloxane may contain said types of functional groups in any combination. The selection of the type of functional groups permits the partitioning of a particular analyte or analyes from the sample The polysiloxane coating may be a polymer, a copolymer or a combination of polymers. 
     Alternatively, sorptive coating  27  may be (1) a porous layer, such as a derivatized etched surface, (2) other immobilized polymers that are above their glass transition temperatures such as poly butadiene, (3) an immobilized porous polymer, such as divinylbenzene, ethyleneglycoldimethacrylate, and copolymers of divinylbenzene and ethyleneglycoldimethacrylate, polyethyleneimine, acrylonitrile, n-vinyl-2-pyrollidinone or 4-vinyl-pyridine, (4) a sol gel or (5) an immobilized adsorbent such as graphatized carbon black. Sorptive coating  27  may be any one of the coatings described or a combination of two or more of the alternative coatings. The selection of the coating or coatings by one skilled in the art is dependent upon the analyte or analytes to be partitioned from sample. 
     Referring again to  FIG. 1 , sample vessel  30  is used to collect sample  15  from which the analyte is to be extracted. Sample vessel  30  is made from a rigid, nonreactive material, such as silica glass, and has a mouth  32 . A cap  34  is used to close the sample vessel  30  at mouth  32 . Cap  34  has an interior surface  35 , within which base  40  of sorption vial  20  selectively attaches. 
     When sample vessel  30  is closed with sorption vial  20  attached to cap  34 , opening  23  faces toward sample  15 . When sample vessel  30  is sealed and inverted, contained liquid sample  15  contacts sorptive coating  27 . Alternatively, sample vessel  30  may be maintained in an upright position with sorption vial  20  exposed to the head space of a collected sample. The analyte within sample  15  is partitioned between sample  15  and sorptive coating  27 . The small surface area of interior surface  22  allows for rapid exchange of a vapor or liquid as well as for desorption by the least volume of solvent. Sorption vial  20  may then be removed from cap  34 , desorbed by a suitable solvent, sealed and stored or transported from the test collection site to a location for testing. 
     The extraction process comprises placing a sample in sample vessel  30 . Sorption vial  20  is then attached to cap  34  or cap liner  37  and sample vessel  30  is sealed. As previously explained, sorption vial  20  is attached within sample vessel  30  such that interior surface  22  will be exposed to samples within sample vessel  30  or the headspace of such samples. Sample vessel  30  may be agitated for a predetermined period of time to allow equilibrated partitioning. Sorption vial  20  is removed from sample vessel  30 . A predetermined amount of elution solvent (not shown) is measured into sorption vial  20 , and sorption vial  20  is sealed. The collected sample may be analyzed by gas chromatography, high performance liquid chromatography or other analytical instruments. Alternatively, the collected sample may be stored for future analysis. 
     In certain cases, such as when a sample has a high viscosity, agitation is not desired. In such cases, collection may take place by exposing sorption vial  20  to the headspace of sample  15 . Sample vessel  30  may be stirred for a predetermined amount of time to enhance equilibrated partitioning. Partitioning takes place between sample  15 , it&#39;s headspace and the sorptive coating  27 . 
     In some cases the volume of sample is equal to or less than the volume of sorption vial  20 . In this case sample vial  20  receives a similar sorptive coating  20  such as PDMS. Sorption vial  20  is then filled with the solution containing analytes to be extracted thus eliminating the need for the sample vessel  30 . A mechanical shaker (not shown) is used to agitate sorption vial  20  and to assist in bringing the partitioning to equilibrium. Sorption vial  20  is emptied and a predetermined amount of elution solvent (not shown) is measured into sorption vial  20 . A vial cap  28  seals sorption vial  20 . The contents (not shown) of sorption vial  20  may then be sampled as required. The preferred embodiment of sample vial  20 , shown in  FIG. 2 , is particularly well suited for this method. 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction may be made within the scope of the appended claims without departing from the spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.