Abstract:
A 96-well solid phase extraction (SPE) plate assembly comprises a common base plate having plural apertures (bores), and removable extraction cartridges (containers, tubes) extending through the bores. The plate assembly is mounted on a conventional 96-well plate vacuum manifold. The cartridges preferably snap into the base plate, but may also screw in. The apertures have annular counterapertures (counterbores) complementary to annular ridges protruding from the side walls of the cartridges. Each ridge snaps into a corresponding counteraperture. The modular design allows the end user to customize the extraction medium mix of the extraction plate assembly by inserting extraction containers having different sorbents into a common base plate. Gaskets are used to maintain a vacuum seal between the base plate and extraction cartridges, for maintaining a pressure gradient across the sorbents.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to systems and methods for extracting solutes from solutions, and in particular to components and methods for solid phase extraction (SPE).  
         BACKGROUND OF THE INVENTION  
         [0002]    In conventional solid phase extraction methods, solutes of interest are isolated from solution by running the solution through a solid phase extraction medium (sorbent) such as coated silica particles. A 96-well solid phase extraction plate is typically placed on a vacuum manifold. The vacuum manifold provides a pressure gradient over sorbents in the plate wells, driving the flow of liquid through the wells. The solutes of interest bind to the extraction medium, while the rest of the solution passes on to collection containers. The solutes of interest can then be recovered by running a suitable solvent through the extraction medium.  
           [0003]    Typical extraction plates are monolithic 96-well plates having identical sorbents in all their wells. For descriptions of such plates see for example U.S. Pat. Nos. 5,417,923, 5,047,215, 5,679,310, and European Patent Publication No. 0576602B1. The end user of a conventional monolithic plate cannot customize the sorbents in different wells of the plate in a practical manner. Thus, an end user investigating different assay methodologies and sorbents for a particular application may need a new 96-well extraction plate for each tested condition, even if only a few wells are required.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides an extraction apparatus comprising a vacuum manifold connected to a vacuum source, defining a collection enclosure; a plurality of collection containers disposed in the collection enclosure; and an extraction plate assembly mounted on the manifold and covering the collection enclosure. The extraction plate assembly comprises a base plate mounted on the manifold, and a plurality of extraction cartridges mounted on the base plate.  
           [0005]    The base plate has a top surface and a bottom surface. A plurality of apertures extend through the base plate from the top surface to the bottom surface. Each extraction cartridge has an inlet and an outlet. Each cartridge is removably locked in a corresponding aperture of the base plate with its inlet situated opposite its outlet relative to the base plate. Locking the extraction cartridges to the base plate allows the end user to reuse the base plate, replace used extraction cartridges, and customize the extraction media of the extraction plate assembly. Reusing the base plate allows the end user to reduce the amount of material discarded with each use.  
           [0006]    Each cartridge comprises a solid-phase extraction medium disposed between its inlet and its outlet, for extracting solutes of interest from a liquid sample inserted into the cartridge through its inlet. Different cartridges of the extraction plate assembly may have different extraction media. Each base plate aperture and cartridge outlet faces a corresponding collection container when the extraction plate assembly is mounted on the manifold, such that the collection container receives liquid from the cartridge outlet.  
           [0007]    Each cartridge is preferably locked to the base plate through a snap-in lock. A snap-in lock allows relatively easy insertion and removal of cartridges from the base plate, and allows multiple linked cartridges to be removed from or inserted into the base plate simultaneously, in one motion. Preferably, the base plate has a counteraperture defined in the side wall of each aperture, and each extraction cartridge has a snap-in ridge for engaging a corresponding counteraperture to snap the cartridge into the base plate. Alternatively, each aperture may have a ridge defined in its side wall, and each cartridge may have a corresponding complementary depression for engaging the ridge.  
           [0008]    The counteraperture is preferably situated at the bottom end of its corresponding aperture, along the bottom surface of the base plate, such that the snap-in ridge is positioned along the bottom surface when the cartridge is locked to the base plate. The counteraperture may also be situated within its corresponding aperture, such that the snap-in ridge is enclosed within the aperture when the extraction cartridge is locked to the base plate. Positioning the counteraperture at a base plate edge allows relatively close spacings between adjacent apertures, by relaxing the constraints imposed on the minimum inter-counteraperture spacing by base plate mechanical stability requirements. Closely spacing adjacent apertures allows increased cartridge fluid-holding volumes as a fraction of the total volume defined by the overall dimensions of the extraction plate assembly.  
           [0009]    In an alternative embodiment, each cartridge is locked to the base plate through a screw-in lock. The base plate then has a helical groove defined in each aperture, and each cartridge has a helical thread complementary to the groove, for engaging the groove to screw the cartridge into the base plate.  
           [0010]    The extraction plate assembly does not allow any substantial air paths therethrough other than through the extraction media. If the seal provided by the locking interface is not sufficient, a gasket may be used to establish a vacuum seal along an interface between each cartridge and the base plate. The gasket is preferably positioned between the top surface of the base plate and a lip of the cartridge. The gasket prevents gas flow through its corresponding base plate aperture, outside the cartridge.  
           [0011]    The present invention further provides a method of making an extraction plate assembly and an extraction apparatus of the present invention. The base plate and extraction cartridges are individually manufactured by injection molding, extrusion, or other known techniques. The extraction cartridges are then locked into the base plate. The resulting extraction plate assembly if mounted onto the manifold, and positioned underneath a fluid-handling apparatus.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1-A shows a perspective view of a preferred extraction apparatus of the present invention.  
         [0013]    [0013]FIG. 1-B shows a side sectional view of the apparatus of FIG. 1-A.  
         [0014]    [0014]FIG. 1-C shows a top view of the apparatus of FIG. 1-A.  
         [0015]    [0015]FIG. 2-A shows a side sectional view of two extraction containers locked in a base plate, according to the preferred embodiment of the present invention.  
         [0016]    [0016]FIG. 2-B shows a top view of one of the extraction containers of FIG. 2-A.  
         [0017]    FIGS.  3 -A through  3 -E illustrate side sectional views of extraction containers locked in base plates, according to respective alternative embodiments of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    In the following description, the term “vacuum” is understood to encompass partial vacuum pressures. The terms “top” and “bottom” are understood to be relative terms characterizing spatial relationships relative to a major plane of a base plate; the terms need not refer to the direction of gravity.  
         [0019]    The following description illustrates embodiments of the invention by way of example and not necessarily by way of limitation.  
         [0020]    [0020]FIG. 1-A shows a perspective view of a preferred extraction apparatus  20  of the present invention. FIGS.  1 -B and  1 -C show side sectional and top views of apparatus  20 , respectively. Apparatus  20  comprises a vacuum manifold  22 , and an extraction plate assembly  26  mounted on manifold  22 . Extraction plate assembly  26  comprises a base plate  30  mounted on manifold  22 , and a plurality of extraction cartridges (containers, tubes)  32  mounted on base plate  30 . Cartridges  32  are locked into base plate  30 , allowing an end user to replace selected cartridges  32  and reuse base plate  30 . Base plate  30  is hatched in FIGS.  1 -B and  1 -C for clarity of presentation. Extraction plate assembly  26  preferably comprises  96  extraction cartridges  32 , each passing through an aperture in base plate  30 .  
         [0021]    As illustrated in FIG. 1-B, each extraction cartridge  32  has an inlet  31  and an outlet  33 . Each cartridge  32  further comprises a conventional extraction solid phase extraction medium (not shown) positioned in the fluid path between inlet  31  and outlet  33 . When cartridge  32  is mounted on base plate  30 , inlet  31  and outlet  33  are situated on opposite sides of base plate  30 . Inlet  31  is formed by an opening at the top of cartridge  32 , above base plate  30 . Outlet  33  is formed by a spout at the bottom of cartridge  32 , underneath base plate  30 . A conventional robotic sample-handling apparatus (not shown) is positioned to insert a sample through inlet  31 . The sample-handling apparatus may constrain the height of extraction apparatus  20  and cartridges  32 .  
         [0022]    Manifold  22  may be a conventional vacuum manifold for holding 96-well collection plates. Manifold  22  comprises a manifold base  24   a,  and a support part  24   b  mounted on manifold base  24   a.  An air conduit  36  is formed in one of the side walls of manifold base  24   a,  for connecting the interior of manifold  22  to a conventional vacuum source such as a vacuum pump (not shown). The direction of air flow through air conduit  36  is illustrated by the arrow  38 .  
         [0023]    Support part  24   b  has a rectangular top aperture for receiving base plate  30 . Base plate  30  is mounted on support part  24   b.  Manifold  22  and extraction plate assembly  26  define a sealed enclosure  34  which is externally connected only through air conduit  36  and extraction containers  32 , as explained in more detail below. Gaskets (not shown) may be provided at the interfaces between manifold base  24   a  and support part  24   b,  and between support part  24   b  and base plate  30 , for sealing enclosure  34 .  
         [0024]    A collection plate  40  is positioned in manifold  22 , within enclosure  34 . Collection plate  40  can be a standard 96-well collection plate. Collection plate  40  comprises a plurality of collection containers  44  each positioned facing a corresponding aperture of base plate  30  and a corresponding outlet  33 . Each collection container  44  is positioned to receive liquid that has passed through a corresponding extraction cartridge  32 .  
         [0025]    The vacuum pump connected to air conduit  36  establishes a partial vacuum within enclosure  34 . Liquid samples each comprising multiple solutes are inserted into inlets  31  by a conventional automatic pipetter (not shown). The pressure gradient across extraction cartridges  32  draws the samples through cartridges  32 . The extraction media within cartridges  32  capture solutes of interest from the samples, while the remaining solutes and solvent are transferred to collection containers  44  through outlets  33 . The solutes of interest can then be eluted from cartridges  32 .  
         [0026]    [0026]FIG. 2-A shows a more detailed side sectional view of part of extraction plate assembly  26 , illustrating part of two extraction cartridges  32   a - b  and base plate  30 . FIG. 2-B shows a top view of extraction cartridge  32   a.  Cartridge  32   b  is similar to cartridge  32   a.  As illustrated in FIG. 2-A, cartridge  32   a  comprises a generally cylindrical fluid-holding body  46   a,  and a tapered outlet spout  60   a  extending downward from fluid-holding body  46   a.  A disk-shaped or cylindrical solid-phase extraction medium  50   a  is positioned in the fluid passage of cartridge  32   a,  at the bottom of fluid-holding body  46   a.  Extraction medium  50   a  is a conventional solid phase extraction (SPE) silica- or polymer-based sorbent. Suitable surface functional groups for the sorbent include cyano, C1, C2, C4, C8, C18, cyclohexyl, phenyl, among others. Extraction medium  50   a  is sandwiched between two conventional frit disks  52   a,    54   a.  Extraction medium  50   a  may be different from the extraction medium  50   b  of cartridge  32   b.    
         [0027]    The frit-sorbent composite formed by frit disks  52   a,    54   a  and extraction medium  50   a  is pressed against the inside side wall of cartridge  32 . Extraction medium  50   a  and frit disks  52   a,    54   a  are supported by a support structure  58   a  extending into the fluid passage of cartridge  32   a,  as illustrated in FIG. 2-B. The transverse cross-section of support structure  58   a  is preferably cross-shaped. Support structure  58   a  prevents the frit-sorbent composite from sagging into outlet spout  60   a  as liquid passes through cartridge  32   a.    
         [0028]    As illustrated in FIG. 2-A, cartridge  32   a  is slidably mounted on base plate  30  through an aperture  62   a.  Aperture  62   a  extends through base plate  30  from a top surface  37  to a bottom surface  39  of base plate  30 . Top surface  37  and bottom surface  39  are preferably substantially planar, parallel surfaces, but may generally include recessed or protruding sections. Aperture  62   a  is preferably a cylindrical bore having an inside diameter substantially equal to the outside diameter of the part of cartridge  32   a  within aperture  62   a.  Aperture  62   a  may generally have a non-circular cross-section, such as a square, rectangular, or oval cross-section.  
         [0029]    Aperture  62   a  has an annular counteraperture (depression, recess)  66   a  defined at the bottom end of its side wall, along bottom surface  39  of base plate  30 . Counteraperture  66   a  lies in a plane perpendicular to the longitudinal axis of aperture  62   a.  Cartridge  32   a  has a snap-in ridge  64   a  protruding from its side wall. Ridge  64   a  is complementary to counteraperture  66   a.  At least part of the surface of ridge  64   a  engages counteraperture  66   a  to snap-in cartridge  32   a  into base plate  30 . Ridge  64   a  preferably has a triangular longitudinal cross-section. The top planar surface of ridge  64   a  abuts counteraperture  66   a,  facilitating the locking and removal of cartridge  32   a.  The bottom planar surface of ridge  64   a  facilitates the insertion of cartridge  32   a  into aperture  62   a.  A free counteraperture  66   c  is shown for an aperture  62   c  in the absence of a corresponding extraction cartridge.  
         [0030]    A PTFE (teflon) or rubber gasket  72   a  is positioned between top surface  37  and a lip  74   a  of cartridge  32   a.  Gasket  72   a  may be provided as part of base plate  30 , and may be attached to base plate  30  by an adhesive. Gasket  72   a  may also be provided as part of cartridge  32   a.  Gasket  72   a  prevents gas flow through aperture  62   a  outside cartridge  32   a,  between the side walls of aperture  62   a  and cartridge  32   a.  Gasket  72   a  establishes a vacuum seal along the interface between cartridge  32   a  and base plate  30 , ensuring that the pressure gradient across base plate  30  efficiently drives the flow of fluid through cartridge  32   a.  Lip  74   a  is preferably defined by the interface between an upper section  76   a  and a lower section  78   a  of fluid holding body  46   a.  Upper section  76   a  has a larger transverse size than lower section  78   a.    
         [0031]    Extraction cartridge  32   a  is preferably made of a plastic such as polypropylene. Other suitable materials for cartridge  32   a  include polyethylene or PTFE. Cartridge  32   a  is preferably made by injection molding. Other suitable methods for forming cartridge  32   a  include extrusion or machining.  
         [0032]    For a 96-well extraction plate assembly, cartridge  32   a  has a fluid-holding volume on the order of a few ml, typically between 1 ml and 5 ml, preferably about 2 ml. The center-to-center spacing between adjacent cartridges  32  on base plate  30  is on the order of mm to cm, preferably about 9 mm. The side wall of cartridge  32   a  preferably has a constant thickness on the order of tenths of mm to mm, preferably about 0.5 mm. Upper section  76   a  of fluid holding body  46   a  has a length on the order of a few cm, preferably about 38 mm, an outside diameter on the order of mm, preferably about 9 mm, and an inside diameter on the order of mm, preferably about 8 mm. Lower section  78   a  of fluid holding body  46   a  has a length on the order of cm, preferably about 17 mm, an outside diameter on the order of mm, preferably about 8 mm, and an inside diameter on the order of mm, preferably about 7 mm. The diameter of aperture  62   a  is equal to the outside diameter of lower section  78   a.    
         [0033]    The distance between lip  74   a  and the center of ridge  64   a  is on the order of mm to cm, preferably about 6.5 mm. Ridge  64   a  has a longitudinal dimension of about 1 mm. The sum of the thickness of gasket  72   a  and the distance between upper surface  37  and lower surface  39  of base plate  30  is about equal to the distance between lip  74   a  and the center of ridge  64   a.  Ridge  64   a  protrudes about 0.25 mm from the side wall of cartridge  32   a.  Counteraperture  66   a  preferably has a depth of about 0.35 mm, and forms angles of about 45° with respect to the side wall of aperture  62   a  and with bottom surface  39  of base plate  30 . The extent of base plate  30  between cartridges  32   a - b  is preferably about 1 mm along aperture  62   a,  and at least 0.3 mm at the bottom of counteraperture  66   a.    
         [0034]    The snap-in attachment of cartridges  32  to base plate  30  allows easy assembly of a heterogeneous extraction plate assembly  26  from cartridges having different extraction media. An end user may obtain extraction cartridges  32  separately from base plate  30 , and then choose the distribution of extraction media to use for extraction plate assembly  26 . A heterogeneous extraction plate assembly allows easily testing multiple extraction media simultaneously, thus facilitating method development, optimization studies, and comparisons or different extraction media. Furthermore, the end user may reuse base plate  30  with new cartridges  32 , or use base plate  30  with only a subset of its potential cartridges  32  by stoppering the unused apertures. By contrast, an end user constrained to use prior-art monolithic extraction plates would need a large number of different extraction plates for testing different extraction media. The end user may need a means of identifying used wells in the monolithic plate, or may need to discard an entire monolithic plate after each use even if a large number of wells within each monolithic plate are not needed for a particular testing method.  
         [0035]    Placing counteraperture  66   a  along an external surface of base plate  30  allows reducing the spacing between adjacent cartridges  32 . A counteraperture internal to the base plate may require larger spacings between adjacent cartridges, since the base plate internal side walls between adjacent counterapertures need to provide sufficient mechanical stability to the base plate. That is, mechanical stability concerns may require larger inter-counteraperture spacings for internal counterapertures than for external counterapertures.  
         [0036]    Placing counteraperture  66   a  along bottom surface  39  and gasket  72   a  along top surface  37  allows easy insertion of cartridge  32   a  from the top of base plate  30 . The transverse cross-sections of cartridge  32   a,  aperture  62   a,  and counteraperture  66   a  are preferably circular for ease of manufacture of cartridge  32   a  and base plate  30 , and for ease of insertion of cartridge  32   a  into base plate  30 . A flat contact surface for the interface between ridge  64   a  and counteraperture  66   a  is preferred for ease of manufacture of cartridge  32   a  and base plate  30 . Defining counteraperture  66   a  in base plate  30  and ridge  64   a  on cartridge  32  may allow the use of fewer mold parts during the manufacture of cartridge  32  than defining a ridge in the base plate and a complementary depression in the cartridge.  
         [0037]    [0037]FIG. 3-A shows a side sectional view of part of an extraction cartridge  132  and a corresponding base plate  130 , according to an alternative embodiment of the present invention. Base plate  130  has an annular counteraperture  166  which is internal to its corresponding aperture  162 . In longitudinal cross-section (in the plane of FIG. 3-A), counteraperture  166  has a curved shape. Cartridge  132  has an annular ridge  164  complementary to counteraperture  166 . The curved surface of the interface between ridge  164  and counteraperture  166  allows an improved fit between cartridge  132  and base plate  130 .  
         [0038]    [0038]FIG. 3-B shows a side sectional view of part of an extraction cartridge  232  and a base plate  230 , according to another alternative embodiment of the present invention. Base plate  230  comprises an aperture  262  extending therethrough. Aperture  262  comprises an upper section  262   a  and a lower section  262   b.  Upper section  262   a  has a larger diameter than lower section  262   b.  A counteraperture  266  is defined in lower section  262   b.  Base plate  230  has a top surface  237  including a recessed portion  237 ′.  
         [0039]    Cartridge  232  comprises a fluid-holding body  246  and an outlet spout  260  extending downward from fluid-holding body  246 . Fluid holding body  246  defines a lip  274  at its interface with outlet spout  260 . Cartridge  232  further comprises a ridge  264  protruding from outlet spout  264 . Ridge  264  is complementary to counteraperture  266 , and engages counteraperture  266  to lock cartridge  232  to base plate  230 . A gasket  272  is sandwiched between lip  274  and recessed portion  237 ′, sealing aperture  262  and preventing air flow outside cartridge  232 .  
         [0040]    Cartridge  232  is part of a monolithic group of cartridges connected by a connection plate  235 . The cartridge group may be for example a strip of 8 or 12 cartridges having identical extraction media. The cartridge group may be collectively locked to and removed from base plate  230 . The cartridge group and connection plate  235  may be formed by an individual molded piece.  
         [0041]    [0041]FIG. 3-C shows a side sectional view of part of an extraction cartridge  332  and a corresponding base plate  330 , according to yet another alternative embodiment of the present invention. Base plate  330  has an aperture  362  extending therethrough. A helical groove  366  is defined in aperture  362 . Helical groove  366  extends through aperture  362 . Cartridge  364  has a helical thread  364  protruding from its side wall. Helical thread  364  is complementary to helical groove  366 , and engages helical groove  366  to screw cartridge  332  into plate  330 .  
         [0042]    [0042]FIG. 3-D shows a side sectional view of part of an extraction cartridge  432  and a corresponding base plate  430 , according to still another alternative embodiment of the present invention. Cartridge  432  has a helical thread  464  protruding from an outlet spout  460 . Helical thread  464  engages a complementary helical groove  466  defined in a lower section  462   b  of an aperture  462 . Outlet spout  460  extends through lower section  462   b.  A fluid-holding body  446  of cartridge  432  extends through an upper section  462   a  of aperture  462 . A gasket  472  rests on base plate  430  at the upper end of upper section  462 . A lip  474  of cartridge  432  is pressed down onto gasket  472 .  
         [0043]    [0043]FIG. 3-E shows a side sectional view of a part of an extraction cartridge  532  and a corresponding base plate  530 , according to yet another alternative embodiment of the present invention. Base plate  530  has an aperture  562  for receiving cartridge  532 . A ridge  564  protrudes from the side wall of aperture  562 . Cartridge  532  has an annular depression (recess, notch)  566  defined in its side wall, for engaging ridge  564  to snap cartridge  532  into base plate  530 .  
         [0044]    It will be clear to one skilled in the art that the above embodiments may be altered in many ways without departing from the scope of the invention. For example, the base plate need not be a monolithic molded part, but may include two or more sandwiched flat sections. More than one counteraperture may be used. Various approaches may be suitable for locking the extraction cartridges to the base plate and providing a vacuum seal between the cartridges and the base plate, including for example press-fitting each cartridge into a corresponding tapered aperture in the base plate. Positive pressure may be used to drive the samples through the extraction cartridges, by connecting each cartridge through an individual tube to a positive pressure source. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents.