Abstract:
A condenser unit for use with a sample preparation device comprises and inner tube, a hollow outer sleeve, and a fluid conduit. The outer sleeve is coaxially disposed around the inner tube to define a condenser body. The fluid conduit is interposed between the inner tube and the outer sleeve. A first portion of the fluid conduit extends along an axial length of the condenser body and a second portion of the fluid conduit extends along a circumferential length of the condenser body. A stirrer assembly for stiring a substance in a container enables a quantity of the substance to be dispensed into and withdrawn from the container during a stirring operation. The stirrer assembly comprises a holow stir rod, a hollow agitator element, and a fluid sampling instrument. The stir rod and agitator element cooperatively define a stirrer assembly interior, such that the fluid sampling instrument can be movably disposed therein. The condenser unit and stirrer assembly can be integrally combined to provide a condenser/stirrer device.

Description:
TECHNICAL FIELD  
         [0001]    The present invention is generally directed to the preparation of sample solutions in vessels. Specifically, the present invention is directed to the stirring of such solutions and the prevention of loss of heated quantities of solution from such vessels through evaporation.  
         BACKGROUND ART  
         [0002]    As part of many drug development processes, an array of test tubes or other such vessels are commonly placed in a heater unit generally consisting of a block of metal with rows and columns of holes to receive the test tubes. The heater unit is often provided as one of many modules integrated in a workstation, wherein each module performs a specific function dictated by the particular development process.  
           [0003]    As an example, FIG. 1 illustrates a conventional liquid sample preparation workstation generally designated  10 . Workstation  10  typically includes a frame  12 , a motor-driven robotic liquid handling module generally designated  20  equipped with a sampling needle  22 , a dilution module generally designated  30 , a heater unit generally designated  40 , and a vessel rack assembly generally designated  50 . Liquid handling module  20  includes a horizontal arm  24  movable along a lateral track  12 A in frame  12  and a vertical arm  26  movable along a lateral track (not shown) in horizontal arm  24 . Sampling needle  22  is mounted in a vertical track (not shown) of vertical arm  26 . Stepper motors (not shown) are typically provided to power the movement of each relevant component of liquid handling module  20  along its associated track. As a result, sampling needle  22  is movable along three axes to perform operations at various locations of workstation  10 .  
           [0004]    Dilution module  30  is of the syringe pump type, and hence includes a syringe  32  and a valve  34 . Dilution module  30  operates to transfer a diluting medium such as solvent from a solvent reservoir  35  over transfer lines  37 A and  37 B to sampling needle  22 . Heater unit  40  includes a rack portion  42  and a lower enclosed portion  44  located behind the front of heater unit  40 . Rack portion  42  is essentially a heat conductive metal plate with an array of wells adapted to support heater vessels  45 , such that heater vessels  45  extend into enclosed portion  44  and are heated by a heating device contained therein. Enclosed portion  44  can also contain magnetic drives situated under each well. When activated, the magnetic drives couple with individual magnetic agitation elements dropped into each heater vessel  44  to stir the media contained in heater vessels  44 .  
           [0005]    Heater vessels  45  are used to contain masses of sample drugs, chemicals, compounds and the like. A heater control device  46  is mounted in front of enclosed portion  44  to enable programming of the heating profile for the quantities of sample solutions contained in heater vessels  45 , and also to activate the magnetic drives. Vessel rack assembly  50  includes a number of rack mounts  52  for supporting vessel racks  54  of various types. Vessel racks  54  are in turn provided to accommodate arrays of vessels of various sizes and design, such as test tubes  56  and  57  and bottles  59 .  
           [0006]    In one general application of workstation  10 , liquid handling module  20  moves into a position over heater unit  40 , and sampling needle  22  is lowered such that its tip  22 A pierces the septum of each heater vessel  45  to dispense a metered quantity of solvent therein. Once the diluted liquid samples are heated to a desired temperature, sampling needle  22  withdraws quantities of the samples from one or more of heater vessels  45  and moves to vessel rack assembly  50 . Sampling needle  22  can then be used to dispense metered quantities of samples into vessels  56 ,  57 , and/or  59  at vessel racks  54 . At this point, a number of operations can occur at rack assembly  50  that will depend on the specific sample preparation and testing procedure being conducted. As one example, samples could be transferred from rack assembly  50  for further processing by analytical equipment such as a high-pressure liquid chromatography apparatus.  
           [0007]    As acknowledged by those skilled in the art, evaporation of the substances contained in heater vessels  45 , especially the solvent, is a recurring problem. Solvent evaporation can result in an undesirable change in the concentration of the chemical constituents in each heater vessel  45 , thereby impairing the validity of the sampling and analytical processes. Accordingly, heater unit  40  has been conventionally equipped with a fan unit  48 , which blows air around the top portions of heater vessels  45  to condense evaporated fluids and particularly the solvent. In this manner, fan unit  48  endeavors to prevent such vapors from escaping heater vessels  45  and causes the vapors to condense onto the walls of heater vessels  45 , such that the condensate returns to the bottom portions of heater vessels  45 .  
           [0008]    This conventional method of blowing room air by the top portions of heater vessels  45 , although quite simple to implement, has proven to be quite ineffective. With the use of fan unit  48 , heat is transferred from the top portions of heater vessels  45  primarily by the mechanism of forced convection. As a general matter, convection occurs when a fluid such as air flows over a solid body or inside a channel while the temperatures of the fluid and the solid surface are different. Heat transfer between the fluid and the solid surface takes place as a consequence of the motion of the fluid relative to the surface. Without fan unit  48 , natural (or free) convective fluid motion would occur as a result of buoyancy forces induced by density gradients in the fluid, which density gradients are the result of temperature gradients directed from the solid surface into the fluid and temperature variations within the fluid itself. Fan unit  48  operates to mechanically induce the fluid motion, which in this case involves forcing the flow of ambient air around the outer surfaces of the top portions of heater vessels  45 .  
           [0009]    It is well known that forced convection such as by a fan or pump significantly increases the rate of heat transfer as compared with natural convection. However, while the forced convection mode of heat transfer can be quite adequate in other contexts, it is inadequate when applied to an array of vessels such as heater vessels  45 . The amount of heat energy added to heater vessels  45  by heater unit  40  and the rate at which such heat energy is added can cause a relatively large quantity of solvent to quickly change into its vaporous phase, such that the forced convection of room air around the top portions of heater vessels  45  does not remove enough heat energy from the top portions to cause the solvent to condense back into liquid phase. As a result, much of the high-temperature evaporated solvent escapes heater vessels  45 , even when septa or other sealing components are provided, due to the temperature and pressure differentials between the interiors of heater vessels  45  and the ambient airspace.  
           [0010]    Another problem stems from the fact that viscous compounds are often processed in heater vessels  45 . It is often required that such compounds be stirred, either constantly or periodically, while being heated. The compounds in heater vessels  45  are often too viscous to be stirred by conventional methods such as by using magnetically driven agitating elements. The problem is exacerbated by the relatively narrow interiors of heater vessels  45  and their close proximity to each other in the vessel array. There is little room around heater vessels  45  for mounting the external magnetic drive assemblies required in the use of magnetic agitation elements. Additionally, there is little room within each individual heater vessel  45  for inserting a paddle or other mechanically driven agitating element in a manner that does not interfere with other components operating within heater vessel  45  such as a sampling cannula.  
           [0011]    The present invention is provided to solve these and other problems associated with the processing of substances within vessels.  
         DISCLOSURE OF THE INVENTION  
         [0012]    Accordingly, the present invention generally provides a compact, fluid-cooled condenser unit constructed from a heat conductive material such as metal. The condenser unit is adapted to fit into the top portion of a sample-containing vessel in order to effectively cool and condense the solvent vapor developed in the vessel and thereby reduce solvent loss from the vessel, all of which is accomplished to a much greater degree than has heretofore been achieved. As will become evident from the description hereinbelow, the condenser unit of the present invention transfers heat from the vessel by presenting several different mechanisms which utilize, to a significant degree, both convection and conduction modes of heat transfer.  
           [0013]    The geometry of the condenser unit is such that a variety of surfaces are present within the top portion of the vessel for enabling heat transfer therefrom. In addition, a conduit for the heat transfer fluid is formed as a multi-pass flow arrangement which, in conjunction with the compactness of the condenser unit, increases the overall effectiveness of the condenser unit as a heat exchanger. A large amount of heat energy is carried away from the vessel by circulating a heat transfer fluid such as water through the condenser unit. This circulation keeps the body and surfaces of the condenser unit quite cool, which in turn sets up a variety of complex temperature gradients along several directions from the localized air and solvent vapor in the top portion of the vessel towards the heat transfer fluid circulating within the condenser unit. Significant convective heat transfer occurs at the surfaces of the condenser unit, at the fluid conduit, as well as at the ambient surface of the top portion of the vessel. Significant conductive heat transfer occurs through the body of the condenser unit, as well as across the wall of the vessel.  
           [0014]    The present invention also generally provides a stirring unit having a configuration which permits the stirring unit to operate constantly within the vessel without detrimentally affecting other procedures being carried out at the vessel. For instance, the stirring unit can operate at the same time a sampling needle is being employed to dispense or withdraw solvent or sample solution to or from the vessel. The stirring unit includes a mechanically driven paddle which provides sufficient power to stir highly viscous liquids, and it more closely mimics the process used as sample products are “scaled up” as understood by those skilled in the art of pharmaceutical development.  
           [0015]    The respective designs of the condenser unit and stirring unit permit each unit to operate together and concurrently within the same vessel. This unique functional combination of paddle stirring and fluid-cooled condensing within the vessel, or within each vessel of a given vessel array, provides a highly useful and effective tool for pharmaceutical development.  
           [0016]    According to one embodiment of the present invention, a condenser unit is adapted to condense an evaporative substance in a container. The condenser unit comprises an inner tube, a hollow outer sleeve, and a fluid conduit. The inner tube includes an inner wall with opposing first and second ends. The outer sleeve includes an outer wall coaxially disposed around the inner wall. The outer wall includes opposing first and second ends. The inner tube and the outer sleeve cooperatively define a condenser body and the second end of the inner wall defines an aperture of the condenser body. The fluid conduit is interposed between the inner tube and the outer sleeve, and includes an inlet end and an outlet end. Preferably, the inlet and outlet ends are each disposed proximate to the respective first ends of the inner tube and the outer sleeve. A first portion of the fluid conduit extends along an axial length of the condenser body, and a second portion of the fluid conduit extends along a circumferential length of the condenser body.  
           [0017]    According to another embodiment of the present invention, a condenser assembly for preventing evaporation from a container comprises a condenser unit and a heat transfer medium circulation system. The condenser unit has opposing first and second ends. The condenser unit includes an inner tube defining a hollow condenser interior, an outer sleeve coaxially disposed around the inner tube, an inlet aperture, and an outlet aperture. The inner tube and the outer sleeve define a condenser body. A sealing element is attached to the first end and includes a first surface extending radially outwardly beyond the outer sleeve. A fluid conduit is interposed between the inner tube and the outer sleeve, and includes an inlet end and an outlet end. Preferably, the inlet and outlet ends are each disposed proximate to the first end of the condenser body. The inlet end is disposed in fluid communication with the inlet aperture and the outlet end is disposed in fluid communication with the outlet aperture. A first portion of the fluid conduit extends along an axial length of the condenser body, and a second portion of the fluid conduit extends along a circumferential length of the condenser body. The heat transfer medium circulation system is connected to the inlet and outlet apertures.  
           [0018]    The condenser assembly is adapted for installation in a container. Such a container includes an open end, a closed end and a hollow container interior. The container can be coaxially disposed around the outer sleeve, such that the open end sealingly contacts the first surface of the sealing element and the second end of the condenser body establishes open communication between the condenser interior and the container interior.  
           [0019]    According to yet another embodiment of the present invention, a heat exchange system for transferring heat from a container comprises a condenser body, a header, a heat exchange conduit and a pump. The condenser body has opposing first and second ends, an inner tube defining a hollow condenser interior, and an outer sleeve coaxially disposed around the inner tube. The header is attached to the first end and includes a fluid inlet fitting, a fluid outlet fitting, and a first surface extending radially outwardly beyond the outer sleeve. The heat exchange conduit is interposed between the inner tube and the outer sleeve, and includes an inlet end and an outlet end. The inlet end is disposed in fluid communication with the inlet fitting, and the outlet end is disposed in fluid communication with the outlet fitting. A first portion of the heat exchange conduit extends along an axial length of the condenser body, and a second portion of the heat exchange conduit extends along a circumferential length of the condenser body. The pump is adapted to circulate a heat transfer medium through the heat exchange conduit. The pump includes a pump outlet connected in fluid communication with the inlet fitting through a pump output conduit, and a pump inlet connected in fluid communication with the outlet fitting through a pump input conduit.  
           [0020]    According to a further embodiment of the present invention, a condensing and heating assembly is provided for heating fluid contained in a fluid container and preventing evaporation of the fluid from the fluid container. The assembly comprises a heating unit, a mounting frame, and a condenser body. The condenser body has an upper end, a lower end, an inner tube, and an outer sleeve coaxially disposed around the inner tube. A fluid conduit is interposed between the inner tube and the outer sleeve, and includes an inlet end-and an outlet end. A first portion of the fluid conduit extends along an axial length of the condenser body, and a second portion of the fluid conduit extends along a circumferential length of the condenser body. A sealing element is sealed to the upper end and attached to the mounting frame, such that the condenser body is disposed proximate to the heating unit.  
           [0021]    According to a still further embodiment of the present invention, a stirrer assembly is provided for stirring a substance contained in a container, and which enables a quantity of the substance to be dispensed into and withdrawn from the container during a stirring operation. The stirrer assembly comprises a stir rod, an agitator element, and a fluid sampling instrument. The stir rod includes opposing first and second open ends and a hollow interior. The hollow interior is situated in open communication with the first and second ends. The agitator element is disposed at the second end of the stir rod. The agitator element includes a tip, a tip aperture, and a hollow interior establishing open communication between the second end of the stir rod and the tip aperture. The stir rod interior and the agitator element interior cooperatively define a stirrer assembly interior. The fluid sampling instrument is movably disposed within the stirrer assembly interior.  
           [0022]    According to an additional embodiment of the present invention, a combined condenser/stirrer device is provided for stirring a substance contained in a container, and for condensing evaporative phases of the substance to prevent the evaporative phases from escaping from the container. An inner tube of the device includes an inner wall. The inner wall includes opposing first and second ends and defines a hollow condenser interior. A hollow outer sleeve includes an outer wall coaxially disposed around the inner wall, and includes opposing first and second ends. The inner tube and the outer sleeve cooperatively define a condenser body. A fluid conduit is interposed between the inner tube and the outer sleeve, and includes an inlet end and an outlet end. A first portion of the fluid conduit extends along an axial length of the condenser body, and a second portion of the fluid conduit extends along a circumferential length of the condenser body. A stir rod extends through the condenser interior and beyond the respective second ends of the inner wall and the outer wall.  
           [0023]    In another embodiment, the present invention provides a sample preparation assembly comprising a plate, a condenser body, a heat exchange conduit, and a stir rod. The condenser body is attached to the plate and includes an inner tube having an inner wall, a hollow outer sleeve having an outer wall, and a heat exchange conduit. The stir rod extends through an aperture of the plate, through an interior of the condenser, and beyond ends of the inner wall and the outer wall. A drive assembly can be operatively connected to the stir rod and adapted to provide rotational energy to the stir rod. A heat transfer medium circulation system can be placed in communication with inlet and outlet ends of the heat exchange conduit. A heater unit can be disposed proximate to the condenser body.  
           [0024]    The present invention also provides a method for preventing the escape of vaporous phases of a substance from a container. A condenser unit is provided in which an outer sleeve is coaxially disposed around an inner tube, and a fluid conduit is interposed between the inner tube and the outer sleeve. A vessel containing a substance is brought into sealed contact with the condenser unit such that the fluid conduit extends into the vessel. A heat transfer medium is circulated through the fluid conduit to cause a vaporous portion of the substance to condense.  
           [0025]    The present invention further provides a method for stirring a substance contained in a vessel. A stirring unit is provided which includes a shaft and an agitator element attached to the shaft, such that the shaft and the agitator element include respective hollow interiors cooperatively defining an elongate bore. The stirring unit is inserted into a vessel containing a substance such that the agitator element is immersed in the substance, and the agitator element is caused to rotate. A sampling instrument is inserted through the elongate bore and beyond the agitator element while the agitator element is rotating, such that a quantity of the substance can be dispensed into the vessel or withdrawn from the vessel.  
           [0026]    It is therefore an object of the present invention to provide a compact condensing device for use in conjunction with a solution-containing vessel, and which exhibits improved heat transfer characteristics.  
           [0027]    It is another object of the present invention to provide a condensing device which enables several significant modes of heat transfer away from the top portion of a vessel.  
           [0028]    It is yet another object of the present invention to provide a condensing device which increases the amount of heat transfer surface area within a vessel.  
           [0029]    It is a further object of the present invention to provide a condensing device which operates within a vessel while another instrument such as a sampling needle operates within the same vessel.  
           [0030]    lt is a still further object of the present invention to provide a condensing device which can be easily integrated into a sample preparation workstation.  
           [0031]    It is an additional object of the present invention to provide a mechanically driven stirring unit for use in conjunction with a solution-containing vessel, and which exhibits improved agitating performance.  
           [0032]    It is also an object of the present invention to provide a stirring unit which operates within a vessel while another instrument such as a sampling needle operates within the same vessel.  
           [0033]    It is another object according to the present invention to provide a stirring unit which can be easily integrated with a condenser unit to form a combined stirring and condensing unit operative within one or more vessels of a sample preparation workstation.  
           [0034]    Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.  
           [0035]    Some of the objects of the invention having been stated hereinabove, other objects will be evident as the description proceeds, when taken in connection with the accompanying drawings as best described hereinbelow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]    [0036]FIG. 1 is a front elevation view of a conventional sample preparation workstation;  
         [0037]    [0037]FIG. 2 is a perspective view of a condenser unit according to the present invention;  
         [0038]    [0038]FIG. 2A is a perspective view of the condenser unit illustrated in FIG. 2 with the addition of cooling fins;  
         [0039]    [0039]FIG. 3 is an exploded view of the condenser unit of FIG. 2;  
         [0040]    [0040]FIG. 4 is a detailed perspective view of a portion of the condenser unit of FIG. 2;  
         [0041]    [0041]FIG. 5 is a perspective view of a condenser assembly according to the present invention;  
         [0042]    [0042]FIG. 6 is a diagram of a heat transfer fluid circulation system according to the present invention;  
         [0043]    [0043]FIG. 7 is a perspective view of a stirring unit according to the present invention;  
         [0044]    [0044]FIG. 8 is an exploded view of a stirring assembly according to the present invention;  
         [0045]    [0045]FIG. 9 is a perspective view of the stirring assembly of FIG. 8 in assembled form;  
         [0046]    [0046]FIG. 10 is a perspective view of a combined stirring and condensing assembly according to the present invention;  
         [0047]    [0047]FIG. 11 is another perspective view of the combined stirring and condensing assembly of FIG. 10;  
         [0048]    [0048]FIG. 12 is a perspective view of the combined stirring and condensing assembly of FIG. 10 installed at a sample preparation workstation in accordance with the present invention; and  
         [0049]    [0049]FIG. 13 is a perspective view of an alternative embodiment of the combined stirring and condensing assembly of FIG. 10. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0050]    Referring to FIGS.  2 - 4 , a condenser unit generally designated  65  is provided in accordance with one aspect of the present invention. As shown in FIG. 2, condenser unit  65  includes a condenser body  70  and a mounting head  90 , each preferably constructed from a good heat conducting material such as steel. As shown in FIG. 3, condenser body  70  includes an inner tube  72  and a coaxial outer sleeve  76 . Structurally, inner tube  72  has an inner wall  74  and outer sleeve  76  has an outer wall  78 . Referring to FIG. 4, inner wall  74  defines a hollow interior  65 A for condenser body  65 .  
         [0051]    A heat exchange conduit  80  for circulating a heat exchange fluid throughout condenser body  70  (thus serving as a condenser coil) is generally interposed between inner tube  72  and outer sleeve  76 . In the preferred embodiment best shown in FIG. 4, heat exchange conduit  80  takes the form of a continuous groove  82  machined into inner wall  74  such that groove  82  and outer wall  78  (see FIG. 3) cooperatively define heat exchange conduit  80 . In order to optimize the effectiveness of condenser body  70  as a heat transfer device, the length of groove  82  is maximized. Engineering within the context of the preferred cylindrical structures illustrated, this optimization is implemented by running groove  82  along an alternating serpentine course, such that groove  82  has many axial sections  82 A running along the height of condenser body  70  and many transitional sections  82 B running generally along circumferential sections of condenser body  70 . It can thus be seen that conduit  80  constitutes a multi-pass flow arrangement which increases the overall effectiveness of condensing unit  65  as a heat exchange device.  
         [0052]    As best shown in FIG. 4, heat exchange conduit  80  begins at an inlet end  84  and terminates at an outlet end  86 . Preferably, both inlet and outlet ends  84  and  86  are located near the top of condenser unit  65 , e.g., near mounting head  90 , so that external fluid lines do not need to be extended down into the vessel in which condenser unit  65  is to operate.  
         [0053]    Referring back to FIG. 2, mounting head  90  has a central bore  92  extending through its axial dimension from a top aperture  92 A to a bottom aperture  92 B (see FIG. 4). Inlet and outlet apertures  94  and  96  are formed on an outside lateral surface  98  of mounting head  90 . Inlet and outlet apertures  94  and  96  are respectively connected in fluid communication with inlet and outlet ends  84  and  86  of heat exchange conduit  80  via internal passages (not shown) within mounting head  90 . A vent hole  101  extends radially from outside lateral surface  98  to bore  92 . As shown in FIG. 4, inner tube  72  is secured to mounting head  90  at bottom aperture  92 B such as by press fitting or micro-welding.  
         [0054]    Referring to FIG. 3, condenser unit  65  is assembled by sliding a seal ring  103  over inner tube  72  until seal ring  103  abuts the underside of mounting head  90 , and by sliding outer sleeve  76  over inner tube  72 . Seal ring  103  is preferably a TEFLON® washer, and serves as a seal for the mouth of a test tube or other vessel into which condenser body  70  is to be inserted. The adjacent ends of inner tube  72  and outer sleeve  76  are micro-welded to ensure that no leaks occur. Using conventional methods, a vent tube  105  is secured at or into vent hole  101 , an inlet fitting  107  is secured at or into inlet aperture  94 , an outlet fitting  109  is secured at or into outlet aperture  96 , and a rotating seal  111  is placed into top aperture  92 A of mounting head  90  and situated above vent hole  101 . Fittings  107  and  109  and apertures  94  and  96  could be provided, for example, with mating threads for fastening purposes. FIG. 2 illustrates condenser unit  65  in assembled form. Condenser unit  65  is quite compact and, for example, has been successfully installed in a test tube having a main outside diameter of 1 inch which tapers down to 0.7 inch near the top.  
         [0055]    In the preferred embodiment, outer sleeve  76  is tightly fit around inner tube  72  in order that heat exchange conduit  80  is tightly sealed. As an alternative, outer sleeve  76  could be radially spaced from inner tube  72  to define an annular chamber (not shown) within which heat exchange conduit  80  could take the form of a small diameter tube running alone a serpentine or helical course.  
         [0056]    It is also preferred that heat exchange conduit  80  be singular and continuous. A plurality of heat exchange conduits  80  could be provided for each condenser unit  65 , but such an alternative would require additional inlet and outlet fittings  107  and  109  and hence additional complexity.  
         [0057]    It can thus be seen that condenser unit  65  can be considered an indirect (or surface) contact-type heat exchanger with multi-pass flow capability.  
         [0058]    Referring to FIG. 2A, condenser unit  65  can alternatively be equipped with a set of annular cooling fins  70 A disposed around the periphery of condenser body  70 . Cooling fins  70 A can be provided as separate components attached to condenser body  70 , or can be formed by reducing the diameter of several sections of condenser body  70 . The addition of cooling fins  70 A can result in improved heat transfer characteristics by increasing the overall surface area available for heat transfer, influencing the direction of fluid flow around condenser body  70 , and/or promoting turbulence. As understood by those skilled in the art, the geometry, size and spacing of cooling fins  70 A must be selected so as to optimize fin efficiency and possibly counteract any resulting increase in thermal or flow resistance.  
         [0059]    Referring to FIG. 5, a condenser assembly generally designated  115  can be constructed by providing a seal plate  120  to serve as an overhead support for one or more condenser units  65 . In the illustrated example, seal plate  120  supports a 2×5 array of ten condenser units  65 . Seal plate  120  preferably includes apertures  122  aligned with each mounting head bore  92  (see FIG. 2) as well as seal plate mounting holes  124  and recesses  126 . As described in more detail below, seal plate  120  can include motor mounting holes  128 , a motor output bore  131 , and a plurality of biasing members such as disk springs  133  extending into each seal plate aperture  122 . In one example, each condenser unit  65  is supported in its corresponding seal plate aperture  122  by an annular ledge or shoulder (not shown) of seal plate aperture  122  or by a second aperture (not shown) of smaller diameter.  
         [0060]    Referring to FIG. 6, a heat transfer fluid circulation system generally designated  140  can be assembled for use in conjunction with one or more condenser units  65 . A suitable fluid pump  142  is provided to transfer a fluid heat transfer medium such as water from a source (not shown) over a pair of input and output lines  144 A and  144 B to and from condenser unit  65 . In the case where several condenser units  65  are employed, an accommodation such as a manifold  146  equipped with valves and directional passages as appropriate can interface with individual pairs of input and output lines  148 A and  148 B associated with each condenser unit  65 .  
         [0061]    Referring to FIG. 12, the present invention provides a novel sample preparation workstation generally designated  200 . Workstation  200  includes a vessel rack assembly generally designated  205  having a framework that includes front rack support members  207  and a rear rack support member  209 . Many of the modules typically utilized in conjunction with liquid handling and/or sample preparation equipment, such as those illustrated in FIG. 1, can be integrated with workstation  200  as appropriate for the procedures contemplated by the user. A heater unit  210  is thus provided to heat an array of heater vessels  212 . A fan unit (e.g., fan unit  40  in FIG. 1), however, is not required. Instead, improved heat exchanging capability is provided in the form of above-described condenser assembly  115 . Accordingly, condenser assembly  115  can be removably mounted to workstation  200  and positioned over heater unit  210  in accordance with the present invention, using suitable mounting components such as mounting brackets  214  and  216  and mounting pins  218  inserted through seal plate mounting holes  122  (see FIG. 5). Seal plate recesses  126  could be utilized to receive removable components (not shown) for transporting condenser assembly  115  to workstation  200  and/or aligning condenser assembly  115  over heater unit  210 , or could be used to mount condenser assembly  115  to another location of workstation  200  (such as vessel rack assembly  205 ) when condenser assembly  115  is in a non-operative standby mode.  
         [0062]    Referring to FIGS.  7 - 9 , a stirring unit in the form of a stir rod generally designated  150  is also provided in accordance with the present invention. Stir rod  150  preferably includes a shaft  152  and an agitator element such as a paddle  154  removably mounted to shaft  152  such as by mated threads. The top of shaft  150  is threaded to receive a plastic cap  156  equipped with a septum  156 A. As shown in FIG. 7, in order to permit an instrument (e.g., sampling needle  22  in FIG. 1, a fiber optic probe, or the like) to pass through stir rod  150  into a vessel in which stir rod  150  is to operate, shaft  152  has a bore  152 A running along its length, and paddle  154  likewise has a bore  154 A extending to its paddle tip  154 B. In order to assist the sampling needle in traversing the length of stir rod  150 , especially where a robotic liquid handling module (e.g., liquid handling module  20  in FIG. 1) is employed, paddle  154  includes a tapered conic section  154 C at the interface between paddle bore  154 A and shaft bore  152 A.  
         [0063]    Referring to FIGS. 8 and 9, a stirring assembly generally designated  155  can be constructed by providing a bearing plate  160  and associated bearing and drive components, all of which are adapted to accommodate one or more stir rods  150 . In the illustrated example, bearing plate  160  supports a 2×5 array of ten stir rods  150 . For this purpose, bearing plate  160  preferably includes apertures  162  through which each corresponding stir rod  150  rotatably extends. Bearing plate  160  can also include motor mounting holes  164  and a motor output bore  166 . A roller bearing  168  is disposed in each bearing plate aperture  162  to rotatably support each corresponding stir rod  150 . Additionally, a stir rod drive gear  171  is fitted onto each stir rod  150 . An endless, flexible drive member such as a polymeric drive chain  173  with double-sided teeth (not specifically shown) is wrapped around drive gears  171  and a motor output gear  175  (see FIG. 10) to provide positive drive capability. If desired, stirring assembly  155  could be operatively mounted to workstation  200  in FIG. 12 apart from condenser assembly  115  to perform agitation procedures.  
         [0064]    Referring to FIGS. 10 and 11, a preferred embodiment of the present invention combines condenser and stirrer assemblies  115  and  155  into an integrated stirrer/condenser or sample preparation assembly generally designated  180 . Bearing plate apertures  162  (see FIG. 8) are aligned with corresponding seal plate apertures  122  (see FIG. 5). Corresponding motor mounting holes  128  and  164  and motor output bores  131  and  166  are also aligned. Shafts  152  of stir rods  150  are inserted through bearing plate apertures  162 , seal plate apertures  122 , mounting head bore  92  (see FIG. 2) and condenser body interiors  65 A (see FIG. 4). Paddles  154  are secured to shafts  152  below condenser units  65 . A motor  182  is installed by inserting appropriate fasteners  184  through motor mounting holes  128  and  164 , a spacer plate  186 , and a motor mounting flange  188 . An output shaft  182 A for motor  182  extends through output bores  131  and  166 , and output gear  175  is fitted thereon. A cover plate  191 , shown in FIG. 11, protects the user from the rotating gears  171  and  175 .  
         [0065]    Referring to FIG. 12, both condenser and stirrer assemblies  115  and  155  (collectively, sample preparation assembly  180 ) are illustrated in operative position at workstation  200 . A paddle speed controller and indicator unit  220  is wired to motor  182 . Disk springs  133  (shown in FIG. 5) are interposed between bearing plate  160  and seal plate  120  and held down by bearing plate  160 , and act to force seal plate  120  downwardly into improved sealing relation with the mouths of each heater vessel  212 . Rotating seals  111  (shown in FIG. 3), positioned in each mounting head bore  92 , prevent heated vapors in heater vessels  212  from escaping around stir rods  150  while allowing stir rods  150  to rotate freely. Vent tubes  105  (best shown in FIGS. 2 and 3) prevent an undue amount of pressure from building up inside heater vessels  212  by providing an escape route for vapors, since each vent tube  105  and its associated vent hole  101  are in open communication with corresponding mounting head bore  92 , condenser body interior  65 A, and the interior of heater vessel  212 . It should be noted however that under normal circumstances, the thermodynamic pressure-volume-temperature (P-V-T) relationship characterizing the condensing procedure dictates that no vapors will leak through vent tubes  105 . This is because condenser assembly  115  causes such vapors to change back to the liquid phase before the vapors have an opportunity to expand into vent tubes  105 .  
         [0066]    It should also be noted that some procedures require that reactions occur in heater vessels  212  in the presence of an inert gas such as diatomic nitrogen or argon. In such cases, vent holes  101  can be used as gas inlets for admitting a quantity of inert gas into heater vessels  212 , and thus vent tubes  105  can be used as the fittings for these gas inlets. Accordingly, as used herein, the term “vent hole” can be taken to mean “gas inlet” and the term “vent tube” can be taken to mean “gas inlet fitting.” 
         [0067]    Referring to FIG. 13, sample preparation assembly  180  can be adapted to operate in conjunction with less than a full array of heater vessels  212 . In such a case, a drive chain  233  of shorter length can be used and, depending on the number of condenser assemblies  115  and/or stirrer assemblies  155  being used and their positions at bearing plate  160 , one or more idler elements  235  can be installed at vacant bearing assembly sites  237 .  
         [0068]    An exemplary general operation of the embodiments of the present invention will now be described with reference to FIG. 12, with secondary reference made to FIG. 1. The researcher places heater vessels  212  containing masses of drugs or the like into heater unit  210 . Stirrer assembly  155 , condenser assembly  115  or combined stirrer/condenser assembly  180  is picked up from a standby position and lowered over the array of heater vessels  212 . The position of stirrer/condenser assembly  180  is established by inserting mounting pins  218  into mounting brackets  214  and  216 . At predetermined time intervals, workstation  200  automatically drives liquid handling module  20  and inserts sampling needle  22  through the septum of each stir rod cap  156 , through corresponding stir rod  150  and into corresponding heater vessel  212 . Dilution module  30  transfers solvent into each heater vessel  212  to dilute the sampled mass therein to an appropriate volume, thereby producing a sample solution. Fluid flow to each operative condenser unit  65  of condenser assembly  115  is established by heat transfer fluid circulation system  140  (see FIG. 6), motor  182  is switched on to drive each operative paddle  154  of stirrer assembly  155 , and heater unit  210  is switched on to heat the sample solutions. Paddle rotation speed can be adjusted by controller and indicator unit  220 .  
         [0069]    At further predetermined time intervals, liquid handling module  20  can be programmed to insert sampling needle  22  back into each heater vessel  212  so that dilution module  30  can withdraw a metered quantity of heated sample solution from heater vessel  212 . Owing to the design of stirring assembly  155 , the sample extraction process can occur while paddles  154  are rotating. Liquid handling module  20  can then be used to deliver the sample solution to locations on rack assembly  205  or to a chemical analysis device as called for by the particular procedure.  
         [0070]    It can be seen from the foregoing description that the design of each condenser unit  65  of condenser assembly  115 , whether or not forming a part of combined stirrer/condenser assembly  180 , is a significant improvement over previous condensing approaches. This is due in part to the fact that each condenser unit  65  generates a large amount of both conduction heat flux and convection heat flux away from the top portion of its associated heater vessel  212 . For the purpose of the present disclosure, heat flux can generally be defined as the amount of heat energy transferred per unit area per unit time. With respect to conduction, the relevant areas are those surface areas which are normal to the direction of temperature gradients and thus heat flow.  
         [0071]    Referring back to FIGS.  2 - 5 , condenser body  70  presents a large amount of surface area through which conductive heat transfer can occur, yet is compact enough to operate within heater vessel  212 . In the present case, conduction heat flux is a function of both the thermal conductivity of the material of condenser body  70  and the temperature gradients directed from the outer surfaces of condenser body  70  to the cooler boundaries of conduit  80  within condenser body  70 . Owing to the configuration of condenser body  80 , temperature gradients are dominant in directions radially inward from the outer surface of outer wall  78  of outer sleeve  76  toward conduit  80 , and in directions radially outward from the inner surface of inner wall  74  of inner tube  72 . The latter directions are perhaps most significant since most of the evaporative solvent will be traveling upwardly into condenser body interior  65 A defined by inner wall  74 . Because a heat transfer medium is constantly being circulated through conduit  80 , and because conduit  80  extends along a lengthy serpentine course, the entire solid portion of condenser body  70  is kept very cool. This results in large temperature gradients, which become the primary factor contributing to the large conduction heat flux. Because thermal conductivity is a less significant factor, a low-cost, moderately conductive material can be selected for condenser body  70 .  
         [0072]    Large amounts of convective heat flux are observed at the boundaries between cooled condenser body  70  and the hot evaporative solvent flowing into condenser body interior  65 A and along the outer surface of condenser body  70 . In addition, the circulation of the heat transfer medium through conduit  80  establishes a strong forced convection which keeps the interfaces between condenser body  70  and conduit  80  cool. In the present case, the convection heat fluxes are a function of the temperature differences between the condenser body surfaces and the vaporous solvent, and between the fluid conduit surfaces and the heat transfer medium. The heat transfer coefficients established at these various boundaries are also a factor. These coefficients depend upon, among other things, the type of fluid flow (i.e., laminar or turbulent) and the geometry of condenser body  70  and conduit  80 . The length and shape of condenser body  70  and its corresponding large surface areas, the multi-pass flow arrangement of conduit  80 , and the continuous circulation of the heat transfer medium through conduit  80 , all result in a large average overall heat transfer coefficient.  
         [0073]    Accordingly, the several heat transfer mechanisms established by condenser unit  65  enable a large amount of heat energy to be quickly dissipated from the solvent vapor and subsequently carried away by the heat transfer medium circulating through conduit  80 . The solvent vapor, upon striking the surfaces of condenser body  70  at a temperature below the saturation temperature of the solvent during normal pressures, will rapidly condense on those surfaces and be prevented from escaping out of heater vessel  212 . It should also be noted that the-condensing function of condenser unit  65  is sufficiently localized within the top portion of heater vessel  212  so as not to impair the heating process performed by heater unit  210  on the sample solution contained in the lower portion of heater vessel  212 .  
         [0074]    It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.