Abstract:
A docking station includes remotely actuated locking mechanisms for secure registration of reaction blocks, and provides for introduction of gases, liquids, and vacuum to the reaction blocks.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 08/718,106, filed Sep. 18, 1996 now abandoned, which is divisional of application Ser. No. 08/422,869, filed Apr. 17, 1995 now U.S. Pat. No. 5,609,826. U.S. Pat. No. 5,609,826 is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to apparatus used in combinatorial synthesis, and more particularly to a reaction block docking station. 
     BACKGROUND 
     The relationship between the structure and function of molecules is a fundamental issue in the study of biological and other chemistry-based systems. Structure-function relationships are important in understanding, for example, the functions of enzymes, cellular communication, and cellular control and feedback mechanisms. Certain macromolecules are known to interact with and bind to other molecules having a specific three-dimensional spatial and electronic distribution. Any macromolecule having such specificity can be considered a receptor, whether the macromolecule is an enzyme, a protein, a glycoprotein, an antibody, an oligonucleotide sequence of DNA, RNA, or the like. The various molecules to which receptors bind are known as ligands. 
     Pharmaceutical drug discovery is one type of research that relies on the study of structure-function relationships. Much contemporary drug discovery involves the discovery of ligands with desirable patterns of specificity for biologically important receptors. Thus, the time necessary to bring new drugs to market could be greatly reduced through the use of methods and apparatus that allow rapid generation and screening of large numbers of ligands. 
     A common way to generate such ligands is to synthesize libraries of ligands on solid phase resins. Techniques for solid phase synthesis of peptides are described, for example, in Atherton and Sheppard,  Solid Phase Peptide Synthesis: A Practical Approach , IRL Press at Oxford University Press, Oxford, England, 1989. Techniques for solid phase synthesis of oligonucleotides are described in, for example, Gait,  Oligonucleotide Synthesis: A Practical Approach , IRL Press at Oxford University Press, Oxford, England, 1984. Both of these references are incorporated herein by reference. 
     Since the introduction of solid phase synthesis methods for peptides, oligonucleotides and other polynucleotides, new methods employing solid phase strategies have been developed that are capable of generating thousands, and in some cases even millions, of individual peptide or nucleic acid polymers using automated or manual techniques. These synthesis strategies, which generate families or libraries of compounds, are generally referred to as “combinatorial chemistry” or “combinatorial synthesis” strategies. 
     To aid in the generation of combinatorial chemical libraries, scientific instruments have been produced that automatically perform many or all of the steps required to generate such libraries. An example of an automated combinatorial chemical library synthesizer is the Model 396 MPS fully automated multiple peptide synthesizer, manufactured by Advanced ChemTech, Inc. (“ACT”) of Louisville, Ky. 
     The Model 396 MPS is capable of generating up to 96 different peptides (or other small molecules) in a single run. The syntheses occur simultaneously, with one amino acid being added to each growing polypeptide chain before addition of the next successive amino acid to any polypeptide chain. Thus, each growing polypeptide chain contains the same number of amino acid residues at the end of each synthesis cycle. The syntheses occur in an ACT proprietary plastic reaction block that has 96 reaction chambers. 
     Although the ACT Model 396 works for its intended purpose, it possesses several shortcomings. For example, since the ACT reaction blocks are machined from a single piece of plastic, they require extremely intricate machining and are quite expensive to manufacture. Moreover, should a portion of a block become damaged or contaminated in some way, the entire reaction block would have to be discarded; there is no way to replace individual portions of an ACT block. An additional drawback of the plastic ACT reaction blocks is that they cannot be efficiently heated or cooled to aid in chemical reactions that may require such heating or cooling. 
     Certain processes and chemistries require that the chemical reagents (which may be reactants, solvents, or reactants dissolved in solvents) be kept under an inert or anhydrous atmosphere to prevent reactive groups from reacting with molecular oxygen, water vapor, or other agents commonly found in air. Examples of atmosphere or moisture sensitive chemistries include peptide chemistry, nucleic acid chemistry, organometallic, heterocyclic, and other chemistries commonly used to construct combinatorial chemical libraries. 
     Although the ACT reaction block can maintain an inert atmosphere when locked in place on the work station of the Model 396 MPS, there is no way to maintain an inert atmosphere once an ACT reaction block is removed from the work station. Thus, the reaction block must remain docked at the work station during the entire synthesis cycle. Since many reactants require several hours to react, this represents significant down time for the Model 396 MPS, as it remains idle during the reaction period. 
     The ACT reaction block includes 96 reaction chambers; however, the compounds generated in the ACT reaction block cannot be transferred directly into a standard 96-well microtiter plate because the distance between the outlets of the reaction chambers is too great. When reactions are complete, the user must transfer the contents of the reaction chambers into an array of 96 flat bottom glass vials supported in a plastic frame. The user must then manually pipette fluid from the glass vials into a microtiter plate for further analysis. 
     U.S. Pat. Nos. 3,944,188 and 4,054,141 to Parker et al. disclose a concentrating vortexing shaker that can receive a thermally conductive vessel block. The vessel block of Parker et al. has a plurality of openings for receiving sample laboratory vessels; the vessel block also has passages through which a hearing or cooling liquid may be passed. After the vessel block of Parker et al. is mounted on the vortexing shaker, an air-tight cover may be attached to the block, forming a chamber over the vessels in the block. A vacuum may then be applied to the chamber. 
     Although the vortexing shaker and vessel block of Parker et al. may be useful to facilitate particular types of chemical reactions (and when only a small number of samples needs to be generated), the structures disclosed in Parker et al. possess many disadvantages that make them unsuitable for use in the efficient generation of chemical libraries. For example, a vacuum or inert atmosphere may be maintained in the vessel block of Parker et al. only when the vessel block is mounted on the vortexing shaker. Moreover, nothing can be added to the vessels of Parker et al. when the air-tight cover is attached to the vessel block. 
     To secure the vessel block of Parker et al. to the vortexing shaker, vacuum and cooling hoses from the vortexing shaker must be attached to the block manually, and the block itself must be secured to the shaker with a manually operated knob. Again, a common objective of combinatorial synthesis is to generate a very large number of compounds. The several manual operations required to use the vessel block and vortexing shaker of Parker et al. therefore make the use of these structures too inefficient and time consuming for use in the generation of very large chemical libraries. 
     In light of the deficiencies in the prior art, there remains a need in the art for an apparatus that allows for the fully automated and rapid generation of combinatorial chemical libraries. 
     SUMMARY 
     The preferred embodiments meet these needs by providing a reaction block docking station that uses remotely actuated locking mechanisms to quickly and automatically secure reaction blocks into the docking station. A preferred docking station allows the reaction blocks to be heated or cooled, provides for introduction of gases or liquids into the reaction blocks, and provides a vacuum source that can be used to remove liquids or gasses from the reaction blocks. A preferred docking station also allows reaction blocks to be removed from the docking station quickly, automatically, and without the leakage of liquids. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a pipetting work station that includes a preferred embodiment of a reaction block docking station. 
     FIG. 2 is an exploded isometric view of a reaction block and its associated hardware according to a preferred embodiment. 
     FIG. 3 is a side cross-sectional view of the reaction block shown in FIG. 2 including a removable bottom seal. 
     FIG. 4 is a side cross-sectional view of the reaction block shown in FIG. 2 including a microtiter plate. 
     FIGS. 5A and 5B show bottom isometric views of the reaction block shown in FIG.  2 . 
     FIG. 6 is a top plan view of the docking station included in FIG.  1 . 
     FIG. 7 is a top isometric view of a docking station according to an alternative embodiment. 
     FIG. 8 is a bottom isometric view of the docking station shown in FIG.  7 . 
     FIG. 9 is a cross sectional view of a connector in the docking stations shown in FIGS. 6 and 7, inserted into a port in the reaction block shown in FIG.  2 . 
     FIG. 10 is a cross sectional view of a connector in the docking stations shown in FIGS. 6 and 7, inserted into a port having a open valve in the reaction block shown in FIG.  2 . 
     FIG. 11 is a cross sectional view of a connector in the docking stations shown in FIGS. 6 and 7, inserted into a port having a closed valve in the reaction block shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     The structure and function of the preferred embodiments can best be understood by reference to the drawings. The reader will note that the same reference numerals appear in multiple figures. Where this is the case, the numerals refer to the same or corresponding structure in those figures. 
     General Operation 
     FIG. 1 is an isometric view showing a portion of an automated pipetting work station  250  as may be used in a preferred embodiment. Automated pipetting work station  250  may be a TECAN 5032 automated pipetting work station (Manufactured by TECAN, AG, Feldbachstrasse 80, CH-8634 Hombrechtikon, Switzerland) with one or more pipetting arms  252 . Pipetting arm  252  attaches to needle assembly  20 . Needle assembly  20  may include a needle  22 , a gas inlet port  30 , and an electrical connection  31 . Work station  250  may also include pipetting needle rinse stations  70 . 
     A reagent container rack  90  may hold several containers  44  of reagents sealed from the outside air with septum seals  46 . Rack  90  is preferably placed on the left side of work station deck  254 . On the right side of work station deck  254  is a docking station  300  for receiving two reaction blocks  140 . Each reaction block  140  preferably contains an array of  48  reaction chambers  110  (see, e.g., FIG.  2 ). A standard 96 well microtiter plate  302  may be mounted below reaction block  140  when product is to be removed from reaction chambers  110 . 
     Reaction Block 
     Referring now to FIG. 2, an exploded isometric view of a reaction block  140  (and its associated hardware) according to a preferred embodiment is shown. Reaction block  140  is preferably machined out of 6061 aluminum and then anodized for additional corrosion protection. Reaction block  140  could also be hard coat anodized and then impregnated with teflon. Additionally, reaction block  140  could be machined or molded from any suitable metal, engineering plastics, filled plastics, crystalline plastics, ceramics, machinable ceramics, or any other material that can withstand the temperature, pressure, and chemical environment to which reaction block  140  will be exposed. If non-metallic materials are used, product reaction could be enhanced by the application of microwaves. If materials transparent to ultraviolet (UV) light are used, product could be cleaved from the synthesis support using UV light, and without the application of an acid or base. 
     Each reaction block  140  preferably holds 48 reaction chambers  110  that are mounted within openings  144 . Reaction chamber  110  is preferably made of an injection molded or extruded polymer such as polypropylene, although polyethylene, teflon, glass, or any other inert material able to withstand the temperature, pressure, and chemical environment to which reaction chamber  110  is exposed could also be used. Reaction chamber  110  preferably also has an internal volume of approximately 2 ml. 
     The lower portion of reaction chamber  110  can receive a frit  124 , which preferably supports a quantity of a synthesis support, such as solid phase resin (not shown). Frit  124  is preferably a 70 micron polyethylene frit, although other types of frits (such as sintered glass, sintered metals, and sintered ceramics) may be used, depending on the type of chemistry to be performed. 
     The lower portion of reaction chamber  110  is preferably connected to an S-shaped trap tube  136 . The purpose of trap tube  136  is to prevent the loss of liquids from reaction chamber  110  (when reaction chamber  110  is not pressurized) by bringing the level of an outlet for liquid above the normal liquid level of reaction chamber  110 . Trap tube  136  connects to a drain tube  138 . As will be discussed below, drain tube  138  will be positioned so as to deposit liquid into a well of a standard 96-well microtiter plate. 
     Each end of reaction block  140  is preferably fitted with two pins  178  to facilitate handling by a robotic gripper (not shown). Each side of reaction block  140  is preferably fitted with one pin  180  to facilitate securing reaction block  140  onto docking station  300 . Robotic manipulation of reaction block  140  makes automation of the entire synthesis process possible. For example, reagents could be introduced into reaction chambers  110  when reaction block  140  is locked onto docking station  300  of pipetting work station  250 . Reaction block  140  could then be moved to a separate docking station  300 , vortexing shaker table, heating or cooling chamber, or any other location or device (not shown) useful in synthesis or the collection of material. 
     In a preferred embodiment, two types of reaction blocks capable of mating directly with a 96 well microtiter plate are contemplated: the 48 reaction chamber  110  (and drain tube  138 ) positions of a first type of (or “A”) block are offset from the 48 reaction chamber and drain tube positions of a second type of (or “B”) block such that a type “A” and a type “B” block can fill every position in a standard 96 well microtiter plate. The ability to deposit material directly into a 96-well microtiter plate eliminates possible contamination and human error problems that are associated with the ACT reaction block discussed above. 
     Reaction block  140  may be color coded for ease of identification, may have identification numbers  320  machined into or printed on the sides, and may also have a bar code  322  printed on the side for identification by machine. 
     Top surfaces of reaction chambers  110  and raised sealing beads  148  are sealed by a sheet of septum material  153 . Septum  153  is preferably manufactured from {fraction (1/10)}″ thermoplastic rubber (TPR) sheet. Septum  153  is retained by a septum retainer plate  155 , which is preferably fastened with six captive screw-type fasteners  156  that attach to openings  157 . Fasteners  156  pass through openings  159  in septum  153 , and screw into machined fastener openings  158 . 
     Reaction block  140  may be sealed from underneath with a bottom seal  220 . An o-ring or quad ring  221  (see FIG. 3) may be used to ensure a gas-tight seal. Bottom seal  220  may include a one-way valve  222  to allow pressure regulation. Bottom seal  220  is preferably fitted to reaction block  140  with screw-type fasteners  224 . As can be seen in FIG. 2, fasteners  224  pass through openings  226  in plate  155 , through openings  228  in septum  153 , through openings  228  in reaction block  140 , and into openings  232  in bottom seal  220 . 
     Bottom seal  220  permits a desired atmosphere or pressure to be maintained within reaction block  140 , allowing reaction block  140  to be moved from location to location (such as to a separate shaker table, not shown) without loss of such atmosphere or pressure. This can be especially useful in chemistries that require long periods of time for reactions to take place. In these situations, such reactions can take place away from the pipetting work station, allowing the pipetting work station to be used for other purposes. 
     In a preferred embodiment, septum retainer plate  155  is machined from 6061 aluminum, and then anodized. However, retainer plate  155  could also be machined or molded from engineering plastics, ceramics, or any other material that can withstand the temperature, pressure, and chemical environment to which retainer plate  155  will be exposed. 
     Plate  155  is also preferably machined with 48 openings  162  positionally matched with openings  144  of reaction block  140  (and thus with the openings of reaction chambers  110 ) to accurately control the compression of the septum  153  between the tops of reaction chambers  110 , and plate  155 . 
     Referring now to FIGS. 3 and 4, side cross-sectional views of reaction block  140  are shown. Steps  177  are machined into the bottom of reaction block  140  to allow reaction block  140  to mate directly with a standard 96-well microtiter plate  302 . Steps  177  also allow mating and sealing with bottom seal  220 . 
     Referring now to FIGS. 5A and 5B, isometric views of the underside of reaction block  140  are shown. The underside of reaction block  140  includes a generally planar surface  190  that includes a plurality of openings  171  and  176 . Openings  176  accommodate drain tube  138  and s-shaped trap tube  136 . The underside of reaction block  140  preferably also includes four gas ports  196 A through  196 D located on bottom surface  198 . 
     Also included on bottom surface  198  is a gas inlet port  200  that connects to a gas outlet port  201  via a machined tunnel (not shown). This allows pressure on the underside of reaction block  140  to be independently controlled when it is sealed by bottom seal  220  (see FIGS.  2  and  3 ). 
     Bottom surface  198  also includes two ports  202 A and  202 B. The interior of reaction block  140  is preferably machined to include passages (not shown) in which a heating or cooling fluid (preferably a gas) can flow if desired. Gas can enter port  202 A and exit through port  202 B, or vice versa. If reaction block  140  is made of material having high thermal stability or thermal mass (such as 6061 aluminum), this arrangement allows reaction block  140  to be quickly and efficiently heated or cooled for chemistries that require such heating or cooling. Ports  196 A-D,  200  and  202  may also serve as guide pin holes to position reaction block  140  properly on docking station  300  (see FIGS. 1,  6 , and  7 ). 
     Finally, a bar magnet  204  may be mounted flush with surface  198 . Bar magnet  204  serves to activate magnetic reed switch  314  mounted in docking station  300  (see FIGS.  1  and  6 ). As will be discussed below, one or more reed switches preferably prevent the operation of work station  250  unless one or more reaction blocks  140  are properly in place. 
     Docking Station 
     Referring now to FIGS. 1 and 6, a docking station  300  according to a preferred embodiment is shown. Docking station  300  preferably includes two stations,  306 A and  306 B, that include cavities for removably receiving reaction blocks  140  of Type “A” and Type “B”, respectively, as discussed above. As is known to those skilled in the art, docking station  300  may also be fitted with the proper motor, gears, and other elements (not shown) necessary for docking station  300  to act as a vortexing shaker, and preferably as a vortexing shaker having a fixed displacement and variable speed. 
     Docking station  300  preferably includes a remotely actuated cam locking mechanism  400 . Cam locking mechanism  400  preferably includes a pneumatic air cylinder  402 , a linkage  404 , and a cam lock  406 . Air cylinder  402  can cause linkage  404  and cam lock  406  to be in an extended position or in a retracted position. When linkages  404  and cam locks  406  are in a retracted position, cam locks  406  can engage pins  180  in the sides of reaction blocks  140 . When linkages  404  and cam locks  406  are in an extended position, cam locks  406  release pins  180 . Remotely actuated cam locking mechanisms  400  therefore allow reaction blocks  140  to be secured to, and released from, stations  306  quickly and automatically. This permits the synthesis process to be fully automated, and allows a greater number of reaction blocks to use docking station  300  per unit time. This is especially important when it is desired to generate a large combinatorial chemical library relatively quickly. 
     Each station  306  preferably includes gas outlet connectors  308 A through  308 D that connect to ports  196 A through  196 D, respectively, in reaction block  140  (see FIG.  5 A). Each station  306  also includes two coolant or heating fluid (i.e., gas or liquid) connectors  310 A and  310 B. Fluid may flow out of connector  310 A and into connector  310 B, or vice versa. In an alternative embodiment, connectors  310 A and  310 B may be electrical connectors that can be used to power a resistive heating element (not shown) within block  140 . 
     FIG. 1 shows fluid lines  320 A and  320 B attached to connectors  310 A and  310 B, respectively. Although not shown in FIGS. 1,  6 , and  7 , independently controllable fluid lines attach to each connector shown in docking station  300 . Connectors  310 A and  310 B connect to ports  202 A and  202 B, respectively in reaction block  140  (See FIG.  5 A). A gas outlet connector  312  that connects to gas inlet port  200  of reaction block  140  is also included in each station  306 . 
     Stations  306 A and  306 B each preferably also include a presence detector  314  that can detect the presence of a reaction block  140 . In a preferred embodiment, presence detector  314  is a magnetic reed switch that senses the presence of magnet  204  on reaction block  140 . In a preferred embodiment, station  306 A, and more specifically the placement of port  310 B, is arranged such that only an A-type reaction block  140  can be fully inserted and locked into position. Similarly, station  306 B, and more specifically the placement of port  310 B, is arranged such that only a B-type reaction block  140  can be fully inserted and locked into position. In an alternative embodiment, stations  306  and blocks  140  may be configured such that either an A-type or B-type reaction block may be placed in either station  306 . In such an embodiment, presence detector  314  (and magnets  204 ) are preferably configured such that station  306  can determine if an inserted reaction block  140  is of the A-type or of the B-type. 
     FIG. 7 shows an alternative embodiment of docking station  300 . The embodiment of FIG. 7 is preferably configured such that both A-type and B-type reaction blocks  140  may be inserted into either station  306 A or  306 B. A presence detector (not shown) is used to determine which type of reaction block is inserted into a particular station  306 . Each station  306  also includes a presence detector  422  that can detect the presence of a microtiter plate. Presence detector  422  is preferably an optical sensor. 
     Docking station  300  of FIG. 7 includes a drain  408  at the bottom of each station  306 . Each station  306  also includes a vacuum source connector  410 . When applied to a vacuum source, vacuum source connector  410  (which is in vacuum communication with station  306 ) allows a vacuum to be applied to the bottom of reaction blocks  140  when they are secured to stations  306 . Such vacuum application may be used to draw liquid from reaction chambers  110  via drain tubes  138  and trap tubes  136  (see, e.g., FIG.  4 ). Docking station  300  of FIG. 7 includes remotely actuated cam locking mechanisms  400  of the type discussed above with respect to FIG.  6 . 
     FIG. 8 is an isometric view of the underside of docking station  300  of FIG.  7 . Pneumatic air cylinders  402  include compressed air line connectors  412 . Connectors  412  are preferably connected to a source of compressed air (not shown) that can be used to operate remotely actuated pneumatic cylinder  402 . Two pneumatic valves  414  are attached to the underside of docking station  300 . Each valve  414  is positioned underneath a drain  408 . A hose (not shown) is used to connect vacuum source connector  410  to connector  416  on valve  414 . Connector  418  is connected to a vacuum source (not shown), and connector  420  is connected to a waste drain (not shown). 
     Referring now to FIG. 9, a cross sectional view of a connector  308 A inserted into port  196 A of reaction block  140  is shown. Although only the interface between connector  308 A and  196 A will be discussed, it will be understood that similar interfaces are preferably included in other connections between reaction block  140  and docking station  300 . In a preferred embodiment, connector  308 A is inserted into port  196 A. In this fashion, connector  308 A acts as a guide pin to ensure proper alignment of reaction block  140  with station  306 A. A gas-tight seal between connector  308 A and port  196 A is preferably provided by quad ring  330 . A quad ring is preferred over a standard o-ring, because a quad ring has less tendency to adhere to surfaces when connector  308 A is removed from port  196 A. 
     FIGS. 10 and 11 show an alternative embodiment of port  196 A. For operations in which inert or other atmosphere must be maintained, a normally closed valve, such as schraeder valve  360 , may be placed in port  196 A. Schraeder valve  360  may be replaced with a bi-directional elastomeric valve (not shown). In operation, connector  308 A is inserted into port  196 A and engages pin  362  of schraeder valve  360 . Connector  308 A also forms a seal against quad ring  330 . Gas flows out of opening  364  and through schraeder valve  360 . When connector  308 A is removed from port  196 A, pin  362  of schraeder valve  360  moves downward, creating a gas-tight seal. 
     EXAMPLE OF OPERATION 
     The many features of the preferred embodiments described above facilitate the relatively quick and efficient generation of chemical libraries. In the following discussion, a synthesis operation involving a type “A” reaction block  140  will be discussed. However, it will be understood that the following discussion will apply equally for a type “B” block as well. 
     In a typical operation, a synthesis support such as solid phase resin is deposited onto each frit  124  in reaction chambers  110 . Reaction block  140  is then assembled as shown in FIG.  2 . Bottom seal  220  may be mounted if reaction block  140  must be moved from place to place while maintaining a desired atmosphere or pressure. 
     Reaction block  140  may then be manually or robotically inserted into station  306 A of docking station  300  on work station  250  (see FIGS. 1,  6 , and  7 ). At this point, microtiter plate  302  is not located in station  306 A. Remotely actuated locking mechanisms  400  (specifically cam locks  406 ) then grip pins  180 , locking reaction block  140  into place. A type “B” reaction block may be simultaneously mounted in station  306 B. 
     Pipetting work station  250  then operates under computer control to deliver the chosen combination of reagents into reaction chambers  110 . Specifically, pipetting needle  22  (as controlled by pipetting arm  252 ) is used to transfer reagents from containers  44  into reaction chambers  110 . The interior and exterior of pipetting needle  22  may be cleaned as necessary in rinse stations  70 . At any time that reaction block  140  is mounted in station  306 A, reaction block  140  may be heated or cooled, pressurized with inert gas, or vortexed as described above. When reaction block  140  is to be removed from station  306 A, remotely actuated cam locking mechanisms  400  (and specifically cam locks  406 ) release pins  180 . Reaction block  140  may then be robotically or manually removed from station  306 A. 
     For reactions that take a considerable amount of time, reaction block  140  may be manually or robotically moved to another docking station  300 , or to some other location while the reactions are taking place. After the syntheses of the desired products has been completed, the products may be cleaved from the synthesis supports using the appropriate reagents. These reagents may be applied at work station  250 , or they may be applied robotically at some other location. If bottom seal  220  had been mounted, it is then removed, and reaction block  140  is mounted onto a microtiter plate  302  in station  306 A. Reaction chambers  110  may then be pressurized, forcing the product out drain tubes  138  and into alternate wells of microtiter plate  302 . Alternatively, a vacuum may be applied to the underside of reaction block  140 . This vacuum pulls the product out of reaction chambers  110  via drain tubes  138  and trap tubes  136 . Microtiter plate  302  is then moved to station  306 B. A type “B” reaction block  140  is mounted on microtiter plate  302 , and product is then deposited into the alternate empty wells of microtiter plate  302  as discussed above. Again, this process allows product to be deposited directly into the wells of a standard microtiter plate, without requiring an intermediate step. 
     The present invention has been described in terms of a referred embodiment. The invention, however, is not limited to the embodiment depicted and described. Rather, the scope of the invention is defined by the appended claims.