Abstract:
A method and apparatus for efficiently performing solid phase extraction techniques for cleanup of samples to be used in analysis for pesticides, food products, etc. An insert to a centrifuge tube is disclosed which provides for mixing the solid and liquid, after which centrifuging is used to separate the liquid from the solid, after processing it through an appropriate filter.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to sample analysis, and more particularly, to an improved method and apparatus for preparation of samples for use in various analytical testing methods. 
       BACKGROUND OF THE INVENTION 
       [0002]    Solid phase extraction (SPE) is an extraction method that uses a solid phase and a liquid phase to isolate one or more components (i.e.; analytes) from a solution. It is usually used to clean up a sample before using a chromatographic or other analytical method to quantify the amount of analyte(s) in the sample. One procedure is to load a solution onto the SPE phase, wash away undesired components, and then wash off the desired analytes with another solvent into a collection tube. Another often use procedure is to pass the analytes through with the solvent and the undesirables remain on the SPE materials. In this case, a wash is not necessary. Present systems and methods for solid phase extraction typically use a disposable cartridge or similar device, and fall into one of three categories as explained below 
         [0003]    Dispersive SPE: This technique uses loose clean-up solids in a centrifuge tube. Solution to be treated is added to the tube and the tube is shaken to mix the contents. The tube is then centrifuged, solids are collected in the bottom of the tube, and the liquid phase is removed by syringe or pipette and transferred to a clean vial. 
         [0004]    SPE Cartridge: This technique uses a syringe barrel that is packed with clean-up solids. The solids are first wetted with the appropriate solvent. Then the solution to be treated is introduced into the cartridge and forced through the cartridge with positive pressure on top of the sample, or drawn through the column using negative pressure from below. 
         [0005]    DPX-Qg Clean-up Pipette: In this method, a pipette containing dispersive clean-up solids is used. The solids are trapped between a filter at the pipette tip and another filter near the top of the pipette barrel. The solution to be treated is drawn up into the pipette using a bulb or automated system and is mixed with the solid materials by repeatedly expelling the liquid out of the pipette tip and refilling the pipette. (Offered by a company known as DPX Labs) 
         [0006]    Each of the foregoing techniques however, has its own specific drawbacks. 
         [0007]    With Dispersive SPE, after the centrifuge step, the liquid remains atop the undesired solids in a centrifuge tube. It can be difficult to extract the liquid from the solids without disturbing the solids in the bottom of the centrifuge tube. Disturbing the solids actually contaminates the liquid. 
         [0008]    With SPE cartridges, additional solvent is required to pre-wet the solids and to wash them after use to ensure that all the analyte is removed. DPX-Qg requires several passes in and out of the pipette; if done by hand this is labor intensive. Hence, these latter two techniques are somewhat more costly than desirable. 
         [0009]    In view of the foregoing, there exists a need in the art for a more efficient manner in which to perform SPE and related sample preparation techniques. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a side view of an exemplary embodiment of the present invention; 
           [0011]      FIG. 2  depicts an exploded view of a specified portion of the embodiment of  FIG. 1 ; 
           [0012]      FIG. 3  shows an alternative embodiment of the present invention; 
           [0013]      FIG. 4  depicts an exploded view of a portion of the embodiment of  FIG. 3 ; 
           [0014]      FIG. 4A  shows a close-up view of a dividing portion of the embodiment of  FIG. 4 ; 
           [0015]      FIG. 5  shows an assembly diagram of a first embodiment of the present invention; 
           [0016]      FIG. 6  shows an assembly diagram of a second embodiment of the present invention; 
           [0017]      FIG. 7  is a more detailed diagram of certain portions of one exemplary embodiment of the invention; and 
           [0018]      FIG. 8  shows the structure associated a series of channels used in one or more embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]      FIG. 1  depicts an exemplary embodiment of the present invention showing a centrifuge tube  102  with an insert  103  contained therein. The bottom portion of the insert  103  is shown in exploded view in  FIG. 2 , with like parts being designated with the same numerals for purposes of explanation. As indicated in  FIG. 1 , an insert  103  comprising ledges  104  is inserted into a centrifuge tube  102 . Optionally, a snap or friction fit may be provided to maintain the insert  103  in the centrifuge tube  102 . 
         [0020]    In the exemplary embodiment shown in  FIGS. 1 and 2 , the side walls of the insert are tapered so as to form a friction fit towards the top of the centrifuge tube  102  but not at the bottom of the insert, where a small gap  206  as shown remains between the centrifuge tube  102  and the insert  103 . Consequently, the insert may be easily slid into centrifuge tube  102 , while still forming a relatively tight friction fit between centrifuge tube  102  and insert  103 . 
         [0021]    Turning to the more detailed view of an exemplary embodiment of the invention shown at  FIG. 2 , the bottom of insert  103  includes an opening  210 , preferably disclosed at the center as shown. A thin layer of filter material  211  sits on the inside bottom surface of the insert  103  as depicted in  FIG. 2 . The filter material may be a membrane or fitted filter with pore size small enough to prevent solids from passing through during centrifugation. Examples of the filter material include, but are not limited to polyethylene, polypropylene, nylon, polytetrafluroethylene (Teflon®) or cellulose) 
         [0022]    A felt or readily compressible pillow  205  is fitted with an insert  103  atop the filter material  211 . Finally, a retainer  213 , which preferably is in the form of a circular ring described later herein, is put in place to hold everything in the insert as shown. In one embodiment, a narrowed portion  215  forms a protuberance around the inner wall of the insert  103  so that the retainer may be snapped fit in place by pushing it from the top past the protuberance  215 . 
         [0023]    In operation, the appropriate amount of SPE solids are loaded into the insert  103  and the solution to be treated is then introduced into the insert  103 . The tube is capped and shaken either by hand or automatic mechanical process. 
         [0024]    Following the shaking step, the tube is centrifuged, forcing the liquid solution out of the bottom of the insert  103  and into centrifuge tube  102 . The insert  103  may then simply be removed and the liquid left in the bottom of centrifuge tube  102 . 
         [0025]      FIG. 3  shows an alternative embodiment of the present invention including an insert  303  inside a centrifuge tube  102 . In the alternative of  FIGS. 3 and 4 , the insert does not have the same type of bottom as shown in  FIG. 2 . More specifically, a dividing portion  410  is utilized where the side walls  412  extend beyond and below said bottom portion as shown. The pillow  401  is installed underneath the dividing portion, with the filter material  403  underneath and a retainer  405  snapped in from below as shown to maintain the entire system in place. The dividing portion includes an opening in the middle as shown in  FIG. 4A , in order to allow fluid to flow through during centrifuging. 
         [0026]    In accordance with this additional embodiment of  FIG. 4 , the pillow  401 , filter  403  and retainer  405  are fit from below the dividing portion  410 , which also serves as the bottom of the section of insert  303  that holds the solution. Optionally, the portion of the walls  412  into which the retainer and other items are fit may also include a protuberance so that the retainer  405  can be snapped fit in place. 
         [0027]      FIG. 5  depicts an assembly diagram of the present invention, showing a more detailed view of the retainer  213  and the inner bottom  501  of the insert  103  of  FIG. 1 . 
         [0028]    As depicted in  501 , a series of protuberances  502 , preferably in the form of radial extending ribs, surround a central opening  210  in the inside surface of the bottom of insert  103 . 
         [0029]    Referring  FIG. 7 , it can be seen that the series of protuberances  502  create channels  702  which may optimally be slanted toward the opening in the center so that fluid is forced towards the center during centrifuging. 
         [0030]    It is noted that in the embodiment indicated in  FIGS. 3 and 4 , the exemplary geometry of the bottom of insert  303  and the retainer are reversed. More specifically, as can be appreciated from  FIGS. 104 , the channels and protuberances should preferably be formed on the retainer, since it is inserted from the bottom of the insert  303 . The geometry of the bottom of the insert  103  shown in  FIG. 5  is replaced in  FIG. 6  with that of the retainer as shown. 
         [0031]    In accordance with the foregoing method and apparatus, an SPE or similar analog preparation method may be utilized by simply mixing liquid and solid in the insert, shaking it, and then centrifuging it, after which the insert may be removed and the prepared liquid ready for testing remains in the bottom of the centrifuge tube as shown. 
         [0032]    While the foregoing describes the preferred embodiment of the invention, various other modifications or additions will be apparent to those skilled in the art. Such modifications are intended to be covered by the following claims appended hereto.