Abstract:
A solid phase extraction plate includes a unitary tray having a plurality of spaced-apart discrete upstanding chambers molded therein with each chamber having a top opening and a bottom nozzle with downwardly tapering sidewalls extending between the top opening and the bottom nozzle. A plurality of solid phase extraction disks are provided and one secured in each of the plurality of chambers without the use of frits or retainer rings utilizing instead tapered sidewalls of the chamber for enabling a press fit of the disks therein.

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 08/905,811 filed Aug. 4, 1997, now U.S. Pat. No. 5,906,796. 
    
    
     The present invention generally relates to assay assemblies for use in the analysis of liquids by a batch process and is more particularly directed to a solid phase extraction plate for the determination of chemical, bio-chemical or biological nature of various liquids. 
     Because of the need for the analysis, or assay, of a great number of small quantities of liquids, array trays and assemblies have been developed whereby individual samples of test liquid are prepared and subjected to analysis by multi-test processing utilizing various extraction mediums. 
     Devices of this type may include a separation medium to which the liquid for analysis are subjected with the medium serving to remove solid/particulate matter from the liquid by filtration or serving as a form of chromatographic medium for selectively separating or indicating a particular characteristic of the fluid being assayed. 
     A typical prior art solid phase extraction plate assembly is shown in U.S. Pat. No. 5,417,923. The assay trays typically have a plurality of wells, for example, 96, arranged in rows and columns in which the solid phase extraction medium is placed and sequentially treated with liquid reagents and washes involved in the assay of interest. 
     It should be appreciated that this type of assay tray typically has dimensions in the order of 3 inches by 5 inches, hence, a 96 compartment, or well, assay tray has very small compartment diameters. Allowing for supporting for wall structure, a typical  96  well assay tray having the wells arranged and a typical 8×12 configuration will have well diameters in the order of 0.3 inches. 
     Accordingly, while the tray with the compartments, or wells, may be formed by injection molding, the insertion of separation medium into each well and the physical requirement of positively supporting the medium within each individual well can be a tedious time-consuming procedure. 
     Typically, not only is it required to dispose a separate medium in each well, but also a means for fixing or holding the medium in the well in a position suitable for separation, or reaction, with liquids later disposed in the well for assay purposes. 
     Heretofore, separation mediums, either in particulate form or in slug, or disk, form have been supported in wells structure by means of frits, or retaining rings, see for example, the structure shown in U.S. Pat. Nos. 5,205,989, 5,264,184, 5,283,039 and 5,417,923. 
     Given the size of the wells, or compartments, in the  96  well assay tray, it can be easily appreciated that the assembly of the small extraction mediums and retainer rings is extremely tedious and, of course, time-consuming and expensive. 
     The present invention provides for a solid phase extraction plate having simplified construction which does not require the use of frits, or the like, and accordingly, enables significant cost-savings in the assembly thereof. 
     SUMMARY OF THE INVENTION 
     A solid phase extraction plate in accordance with the present invention generally includes a unitary tray having a plurality of spaced-apart discrete, upstanding chambers molded therein. Each chamber includes a top opening and a bottom nozzle. A plurality of solid phase extraction disks are provided with one of the plurality of disks press fitted between the sidewalls of one of the plurality of changes proximate the bottom nozzle. Each disk comprises an extraction medium and silica gel in glass fibers. 
     The tapering sidewalls of the chamber provide a fritless means for receiving one of the plurality of solid phase extraction disks. Because no separate retaining rings, or frits, are required to support or maintain the solid phase extraction disks within the chambers, assembly of the solid phase extraction plate is greatly simplified. 
     More particularly, each of the chamber may have a circular cross section and, in addition, means may be provided for spacing each of the disks from a corresponding nozzle. The structure corresponding to this means for spacing includes a step formed in the sidewall of the chamber proximate the corresponding nozzle. Importantly, this structure also provides means for enabling fluid flow through each of the disks over a diameter of the disk which is greater than the diameter of a nozzle entry port. In this manner, efficient use of each disk is enabled by providing exposed areas on each side of the disk to facilitate fluid flow therethrough. This should be contrasted with prior art devices in which large portion of the extraction medium is masked by abutment with supporting structure. 
     While each of the chambers may have differing cross sections or diameter, it is preferable that each of the chambers be identical in order to facilitate assembly of the extraction disks therein. 
     More particularly, each of the disks may comprise a non-polar medium, polar medium, cation exchange medium, or an anion exchange medium. All of the disks may be of the same medium or different mediums. Still more particularly, the disks may comprise a combination of mediums, for example, both a non-polar/strong cation medium and a polar/strong cation medium. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages and features of the present invention will be better understood by the following description when considered in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a top plan view of a solid phase extraction plate in accordance with the present invention generally showing a unitary tray having a plurality of spaced apart discrete upstanding chambers molded therein; 
     FIG. 2 is a bottom view of the unitary tray shown in FIG. 1; 
     FIG. 3 is a side view of the tray shown in FIGS. 1 and 2; 
     FIG. 4 is aa section of the tray taken along the line  4 — 4  of FIG. 1; 
     FIG. 5 is a part sectional view taken along the line  5 — 5  of FIG. 1; and 
     FIG. 6 is a detail of a bottom portion of one of the chambers showing the disposition of a plurality of extraction disks therein. 
    
    
     DETAILED DESCRIPTION 
     Turning now to FIGS. 1-3, there is shown a solid phase extraction plate  10  in accordance with the present invention, which generally includes a unitary tray  12  having a plurality of spaced apart discrete upstanding chambers  14  molded therein. The tray  12  may be molded from any suitable material such as, for example, polypropylene. 
     Each chamber  14  has a top opening  16  and a bottom nozzle  18 , see also FIGS. 4-6. On disk  28 A may be disposed in each chamber  14  as shown in FIG.  4 . 
     Importantly, sidewalls  24  of the chambers  14  taper downwardly from the openings  16  to the nozzle  18  to provide a fritless means for enabling each disk  28 A to be press fit into corresponding chamber  14  as hereinafter discussed. 
     As most clearly shown in FIG. 6, a plurality of solid phase extraction disks  28 B may be press fitted between the sidewalls  24  of each of the plurality of chambers  14  proximate the bottom nozzle  18 . 
     The disks  28 A,  28 B are formed from silica gel in glass fibers with organic moieties, or mediums, attached via organosilane type chemistries. A wide variety of disks with various medium are available from ANSYS DIAGNOSTICS, INC., Lake Forest, Calif., under the trade name SPECE®. For example, the medium may be non-polar (SPEC C 18 AR, C18, PH, C8, C2); Polar (SPEC CN, NH2, PSA, SI); cation exchange (SPEC SCX); Anion exchange (SPEC, NH2, SAX) or a combination. Mixed phases of non-polar/strong cation and slightly polar/strong cation (SPEC MPI) may also be used. 
     Further, the disks  28 A,  28 B, may have different extraction mediums for desired purposes. 
     Because of the tapering nature of the sidewalls  24 , the disks  28 A,  28 B are held in position proximate the nozzle  18  by frictional engagement with the side walls  24  and are disposed within the chambers  14  by use of a set of ramrods, not shown. This facilitates placement of the disks  28 A in all of the chamber  14  simultaneously. Because no frits or retaining rings (not shown) are utilized, assembly of the solid phase extraction plate  10  is greatly facilitated. The use of polypropylene with wall thickness hereinafter specified provides sufficient resiliency to maintain the disks  28 A,  28 B, within the chambers  14  by frictional contact therewith. 
     As a specific example, the solid phase extraction plate  10  may include the plate  12  having dimensions of about 3 inches wide by 5 inches long, with 96 of the chambers  24  arranged in an array, that is, 8 chambers wide by 12 chambers long. 
     Importantly, as shown in FIG. 5, the chambers  24  taper with a top inside diameter D t  of about 0.325 plus or minus 0.003 inches to a bottom inside diameter D b  of 0.294 plus or minus 0.001 inches. This enables the disk  28 , which has a thickness of about 0.04 inches and a diameter slightly larger than 0.294 inches to be easily inserted through the top opening  16  and forced to a bottom  30  of each chamber proximate the nozzle  18 . 
     Sidewall  24  thicknesses are varied to produce this taper inasmuch as the chambers are unitarily formed in the tray  12  by any suitable molding operation with the sidewalls having a nominal thickness of about 0.032 inches. Overall, the chambers may have a height, H, of about 1.18 inches as indicated in FIG. 4. A surrounding flange  32  is provided for alignment of the chambers  24  with corresponding and accompanying assay apparatus (not shown) for depositing liquid into the openings  16  of the chambers  14 . 
     Turning again to FIG. 6, it can be seen that the nozzle  18  includes an entry port  36  which is smaller than the bottom diameter D b  of the chamber  14 . 
     In order to support the disk  28  proximate that nozzle and create a void  40  therebetween, which may have a thickness T of about 0.04 inches, the disks  28  are supported by steps  44  formed in the sidewall  24  proximate the nozzle  18 . The step  44  not only provides a means for spacing each disk  28 A,  28 B of the nozzle  18 , but also provides a means for enabling fluid flow through each disk  28  over a diameter greater than the nozzle entry port  36  diameter. Because the disks  28 A,  28 B are not held against the top  46  of the nozzle  18 , which is part of the bottom  30  of the chamber  14 , flow may pass through the disks  28 A,  28 B over almost its entire surface area. Only where contact with the step  44  is made is straight through flow not enables. This arrangement significantly improves the efficiency, thus an area having a diameter D v  as shown in FIG. 6 is available for transfer of fluids through the disk, rather than the size of the nozzle entry port  36 . 
     Although there has been hereinabove described specific arrangements of a solid phase extraction plate in accordance with the present invention for the purpose of illustrating the manner in which the present invention can be used to advantage, it should be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements, which may occur to those skilled in the art, should be considered to be within he scope and spared of the present invention as defined by the appended claims.