Abstract:
A device for extracting an analyte from a sample matrix comprises a sorption cap or closure which is coated on the inside surface with a sorbent material. A method for extracting an analyte from a sample matrix includes exposing the cap sorptive coating to the sample matrix by sealing the sample bottle or vial with the sorption cap. After the analyte is collected in the sorbent material, the sorption cap may be removed from the sample container and used to seal an analytical vial containing a small amount of an elution solvent. The analytical vial with sorptive cap may then be stored or transported to a lab for further analysis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part under 37 CFR 1.53(b) to application Ser. No. 10/663,955, “Direct Vial Surface Sorbent Micro Extraction Device and Method,” filed on Sep. 16, 2003 by Robert Wohleb. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     This invention relates to the extraction of one or more analytes by a sorption process. Specifically, this invention relates to a device and method for performing direct vial extraction and desorption. Additionally, this invention relates to a device and method for direct vial purification.  
         [0005]     2. Description of the Related Art  
         [0006]     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 new trend in the industry is toward simplified sample preparation that results in reduced waste and pollutants.  
         [0007]     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. 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.  
         [0008]     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.  
         [0009]     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.  
         [0010]     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.  
         [0011]     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.  
         [0012]     Additionally, a sample may contain contaminants that interfere with analysis of the sample. Thus, it may be desirable to purify the sample by removing the contaminants before attempting to extract the analyte. SPE is commonly used to remove contaminants, with a particulate material, such as silica, packed in the barrel. As previously discussed, SPE requires large amounts of solvent and particulate material.  
         [0013]     Examples of the prior art follow:  
         [0014]     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.  
         [0015]     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. Because adsorption occurs on the inner surface of the needle, the components of interest are not readily storable.  
         [0016]     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.  
         [0017]     Canadian Pat. No. 2,280,418, issued to Forsyth on Feb. 12, 2001, discloses a technique for carrying out solid phase microextraction of analytes contained within a liquid, solid or other material. A fiber assembly is mounted in the headspace of a gas-tight container. A coating is applied to the fiber assembly based on selectivity of the coating towards at least one analyte present in the sample. The fiber assembly is exposed either in direct contact with the sample, or indirectly through contact with the gas present in the headspace of the container. After exposure, the analyte-containing fiber is then desorbed so the desired analyte can be analyzed. There are two alternatives for desorption under Forsyth. The coating must be removed from the fiber through solvent swell. Once the coating has been removed, the coating is placed in an autosampler vial containing a portion of solvent. The coating is suspended in the solvent, which can result in contamination and interference with the autosampler. Additionally, while this method reduces the amount of solvent necessary in the prior art, this method still requires a greater amount of solvent than the present invention. Alternatively, the coating can be left on the fiber and the fiber can be placed in the autosampler vial with a portion of solvent. However, this method still presents problems with autosampler contamination and operation.  
         [0018]     An article entitled, “Headspace Sorptive Extraction (HSSE)” was published on an unspecified date by Tienpont, B. et al. at http://www.richrom.com/assets/CD23PDF/d43.pdf. The article discloses a glass rod support coated with a sorptive coating and suspended in the headspace of a closed container, which contains the analyte-bearing sample. The glass rod remains suspended above the analyte-bearing sample until equilibrium is reached. The glass rod is then removed from the closed container and undergoes thermal desorption.  
         [0019]     Therefore, it would be an improvement in the art to have a device in which the extraction may be performed and the analyte conveniently and transportably stored for later analysis. It would also be an improvement in the art to have a device that minimizes labor and equipment necessary for extraction and desorption. It would also be an improvement in the art to have a device in which desorption may be performed easily, in which the amount of solvent waste is reduced, and that minimizes interference with the autosampler. Additionally, it would be an improvement in the art to have a device that removes contaminants in a sample and reduces waste and equipment. It would also be an improvement in the art to have a device that performs both extraction and purification, thereby further reducing waste and equipment.  
       BRIEF SUMMARY OF THE INVENTION  
       [0020]     The present invention comprises a device and method for extracting analytes and/or removing contaminants from a sample.  
         [0021]     Accordingly, the objects of my invention are to provide, inter alia, a solid phase extraction system that: 
        minimizes the amount of solvent used;     minimizes the amount of labor required;     minimizes glassware;     allows samples to be archived;     allows extraction or purification 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;     eliminates interference with gas or liquid chromatography autosamplers;     reduces or eliminates sample cross contamination;     allows desorption of the analyte; and     does not require expensive thermal desorption equipment.        
 
         [0035]     This invention is a cap coated with either a sorptive coating or a particulate coating, wherein the coated cap is placed over an opening to a vessel containing a sample fluid. Upon exposure to the sorptive coating, the desired analytes are extracted from the sample. Similarly, upon exposure to the particulate coating, the contaminants are removed from the sample. The coated cap may be removed and replaced by an uncoated cap for transportation or storage of the sample. The analyte is then desorbed by attaching the sorptive-coated cap onto a vessel containing a portion of solvent and agitating the vessel.  
         [0036]     Additionally, the particulate-coated cap may be used in conjunction with a sorption vial including a sorptive coating. Alternatively, a sorptive-coated cap may be used in conjunction with a particulate coated vial. When the sample comes in contact with the sorptive and particulate coatings, the particulate coating removes contaminants in the sample while the sorptive coating extracts the desired analytes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]      FIG. 1  is a cross-sectional view of the inventive cap.  
         [0038]      FIG. 2  is a cross-sectional view of a sample vessel.  
         [0039]      FIG. 3  is a cross sectional view of the inventive cap with a syringe-permeable membrane.  
         [0040]      FIG. 4A  is a cross-sectional view of a screw cap.  
         [0041]      FIG. 4B  is a cross-sectional view of a plug cap and sorption vial.  
         [0042]      FIG. 4C  is a cross-sectional view of a snap cap and sorption vial.  
         [0043]      FIG. 4D  is a cross sectional view of a crimp cap and sorption vial.  
         [0044]      FIG. 5  is a cross sectional view of a coated sorption vial. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0045]     Referring to  FIGS. 1-2 , an embodiment of the inventive cap is depicted as  300 . Sidewall  301  and top cover  310  are integrally formed and define the boundaries of cap  300 . Sidewall  301  has sidewall exterior surface  302  and sidewall interior surface  324 . Top cover  310  includes top cover exterior surface  312  and top cover interior surface  313 . Top cover  310  has a cover periphery  316 , which defines the boundary of top cover  310 . Sidewall interior surface  324  and top cover interior surface  313  define cavity  330 . Top interior surface  313  is coated with either a sorptive coating or a particulate coating to create coated surface  322 . Coated surface  322  extends into cavity  330 . Top cover  310  may be solid, or may have a syringe-permeable orifice  319 , as seen in  FIG. 3 .  
         [0046]     Referring to  FIG. 2 , cap  300  is used to close vessel  100  at neck  140 . Vessel  100  is used to provide an analyte-bearing sample  105  from which the analytes are to be extracted. Vessel  100  is made from a rigid, nonreactive material, such as silica glass. Vessel  100  may be of any type, including various forms of flasks and vials known in the art. Vessel  100  defines enclosed chamber  110  wherein sample  105  is held, neck  140 , and at least one vessel opening  102  through which sample  105  enters vessel  100 . Neck  140  defines passageway  122 . Opening  102  provides fluid communication from a sample source (not shown), through passageway  122 , and into chamber  110 .  
         [0047]     Neck  140  is configured so that cap  300  may attach to it and prevent fluid escape from chamber  110 . Cavity  330  receives neck  140 , and sidewall  301  holds top cover  310  over vessel opening  102  in a position preventing fluid communication between passageway  122  and the area external vessel  100 . When cap  300  is attached to vessel  100 , coated surface  322  faces chamber  110  of vessel  100 .  
         [0048]     Referring to  FIG. 3 , an alternative embodiment of cap  300  is depicted. Syringe-permeable member  319  permits a needle (not shown) to pass through top cover  310 . Syringe permeable member  319  is contiguously formed with top cover  310 . Syringe permeable member  319  is semi-permeable and prevents fluid from escaping cap  300 . However, a sharp object (not shown), such as a syringe needle, can pierce through syringe permeable member  319  and enter cavity  330 .  
         [0049]     Various means may be used for interface between cap  300  and vessel  200 . Cap  300  can be a screw-on type cap, a crimp cap, a stopper that plugs into neck  260 , or a snap-on cap.  
         [0050]     Referring to  FIGS. 4A and 5 , sidewall  301  is attached around cover periphery  316 . In one embodiment, sidewall  301  extends from top cover exterior surface  312 , past coated surface  322  and on to sidewall end  308  distal coated surface  322 . At least one cap thread  306  is helically attached along the cap interior surface  320  of sidewall  301 . In this embodiment, cap  300  attaches to vessel  200 . Neck  260  has at least one neck thread  264  helically attached around neck exterior surface  268 . Cap thread  306  and neck thread  264  permit cap  300  to be rotationally connected to neck  260 .  
         [0051]     In another embodiment, as depicted in  FIG. 4B , sidewall  301  extends from cover periphery  316  to lower periphery  328 . Cover periphery diameter  318  is larger than lower periphery diameter  329 . Thus, sidewall  301  tapers as sidewall  301  extends from cover periphery  316 , past coated surface  322 , and on to lower periphery  328 . Cover periphery diameter  318  is larger than neck interior diameter  267 , and lower periphery diameter  329  is smaller than neck interior diameter  267 . Therefore, lower periphery  328  inserts into passageway  266  and top cover  310  is depressed until neck interior surface  263  snugly retains sidewall  301  in an interference fit.  
         [0052]     In yet another embodiment, as depicted in  FIG. 4C , sidewall  301  extends from top surface  312 , past coated surface  322  and on to sidewall end  308  distal coated surface  322 . Proximate sidewall end  308 , sidewall  301  forms lip  304 , which inwardly protrudes from cap interior surface  320 . In order for engagement between cap  300  and neck  260 , neck  260  provides rim  264 . Cap  300  attachedly seals onto vessel  200  when top surface  312  is depressed and lip  304  snaps over rim  264 .  
         [0053]     In yet another embodiment, as depicted in  FIG. 4D , side wall  301  extends from top surface  312 , past coated surface  322  and on to sidewall end  308  distal coated surface  322 . At least one cap thread  306  is attached along cap interior surface  320  of sidewall  302  such that cap thread  306  is ring-shaped and has a smaller thread diameter  307  than sidewall diameter  303 . To accommodate this embodiment, vessel  200  may have neck thread  264  around neck  260  with a larger neck thread diameter  265  than neck exterior diameter  261 .  
         [0054]     Referring to  FIG. 5 , vessel  200  is defined by vial exterior wall  215  and vial base  250 . Vessel  200  has a cylindrically, shaped interior wall  210  with a conically-shaped bottom surface  220 . Vessel  200  also has a vial neck  260  through which there is an opening  262  to bottom surface  220 . Bottom surface  220  is oriented such that the vertex  224  of the conical bottom surface  220  is proximate vial base  250  while the directrix  226  is contiguous with interior wall  210 . Either a sorptive coating or a particulate coating is applied proximate the vertex  224  of interior wall  210 . Alternatively, vessel  200  can have a cylindrical interior wall  210  without a conical bottom surface. When vessel  200  has a cylindrical interior wall  210 , a coating may be applied at any point on interior wall  210 .  
         [0055]     In one embodiment of the invention, a sorptive coating and particulate coating are used in conjunction to extract analytes and purify the sample, respectively. Referring to  FIG. 5 , coated surface  222  is a particulate coating and is applied to interior wall  210  of vessel  200 . Referring to  FIG. 1 , coated surface  322  is a sorptive coating and is applied to cap interior surface  320  of cap  300 . Sample  105  is introduced to vessel  200  via vial opening  262 . Cap  300  is then attachedly engaged with vessel  200  by one of the methods discussed above. Vessel  200  is agitated by a mechanical shaker (not shown) for a predetermined period of time, exposing analyte-bearing sample  105  to the particulate and sorptive coatings. Sorptive coating  322  sorptively extracts at least one analyte present in analyte-bearing sample  105 , and particulate coating  222  removes at least one contaminant present in analyte-bearing sample  105 . Cap  300  is removed and the remaining analyte-bearing sample  105  in vessel  200  is either archived or disposed. Cap  300  is then attached to a vessel  200 , which is filled with solvent. The second vessel  200  is agitated for a predetermined period of time, allowing desorption to occur. After desorption, the analyte-bearing solvent is ready for analysis.  
         [0056]     Alternatively, coated surface  222  and coated surface  322  may each contain a particulate coating or a sorptive coating, as determined for a specific test.  
         [0057]     In the preferred embodiment, the sorptive coating 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.  
         [0058]     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, alkylaryl, 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.  
         [0059]     Alternatively, sorptive coating 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 polybutadiene, (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 may be any one of the coatings described or a combination of two or more of the alternative coatings. Additionally, sorptive coating may be derivatized silica beads. The silica beads are derivatized by octadecyl (C 18 ), octyl (C 8 ), butyl (C 4 ), sorbent quartenary amine (SAX), benzenesulfonic acid (SCX), aminopropyl, cyano, phenyl or carboxylic acid. The derivatized silica is immobilized by a fibrous mesh, or any other mechanical means. 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.  
         [0060]     Acceptable particulate coatings for use in purifying a sample include molecular sieves, activated alumina, silica, silica gel, and ion exchange resins. The selection of particulate coating by one skilled in the art is dependent upon the contaminants targeted and the analytes present in the sample.  
         [0061]     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.