Abstract:
An apparatus for concentrating solutions in a vaporising receptacle ( 1 ) is provided wherein the receptacle ( 1 ) has a mouth ( 3 ), and the axis of the receptacle is perpendicular to the mouth. The apparatus comprises: support means ( 7 ) for supporting the vaporising receptacle with the mouth of the receptacle uppermost and the axis substantially vertical; rotation means ( 89 ) being operable to rotate the vaporising receptacle at high speed substantially about the axis; means ( 13 ) for sealing the vaporising receptacle to the apparatus; a vacuum pump ( 46 ) to reduce the pressure within the vaporising receptacle; means ( 22 ) for dispensing into the vaporising receptacle a solution to be concentrated; sensing means ( 21 ) to measure the temperature of the solution within the vaporising receptacle; heating means ( 19, 99 ) to apply heat to the solution within the vaporising receptacle; a control and regulating unit ( 75 ) for controlling or regulating at least one of said rotation means, said vacuum pump, said dispensing means, said sensing means and said heating means. The invention allows low pressure evaporation in regularly sized and shaped receptacles without bumping, and is also easy to use. A corresponding method is provided.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an apparatus and method for evaporating liquids, particularly, but not exclusively for the purposes of either increasing the concentration of a solution and/or for the complete removal of a solvent from a solution to leave a dry solid. 
       BACKGROUND TO THE INVENTION 
       [0002]    In practice an apparatus for this purpose is known which is generally referred to as a rotation evaporator. An apparatus of this kind is disclosed in U.S. Pat. No. 2,797,747. The receptacle of this rotation evaporator, formed as a round bottomed distilling flask in borosilicate glass, is rotated about its axis by means of a motor during distillation and is connected via a rotary union to a condenser. A vacuum source, for example a diaphragm pump, is connected to the condenser. As a heating arrangement a so called heating bath is used, preferably having a liquid heat transfer medium that can be heated by means of an immersion heater. 
         [0003]    While rotation evaporators of this type offer rapid evaporation and have therefore been widely adopted in Chemistry and Biology laboratories they have limitations. Rotation evaporators require significant expertise and constant adjustment to achieve rapid evaporation without bumping (evaporating in an explosive manner), spitting or foaming of the solution being concentrated. 
         [0004]    Furthermore, the solution must be placed in a suitable receptacle for evaporation, typically a round bottom distillation flask; such a receptacle is impractical for future storage or transportation of concentrated or dry products. Often therefore, after the solution has been concentrated these dry products must be removed from the distilling flask and transferred to a more suitable receptacle, a vial with a screw cap for example. Commonly this transfer process is non trivial requiring multiple distillations and scraping of dry or semi-dry products from the distillation flask, thus requiring significant laboratory staffing time and resulting in loss of product and the potential for contamination. 
         [0005]    Centrifugal evaporators are also known, such as that described in GB 2 384 724A. In such evaporators, sample tubes are mounted to a central rotor and spun about a central axis perpendicular to the axis of the sample tubes. The centrifugal forces acting on the solution in the tubes allows evaporation under vacuum without bumping. However, such evaporators are slow batch processes and as such are unsuitable for incorporation into the modern automated synthesis and purification processes. These modern processes are predominantly sequential and require integrating with evaporation processes providing rapid evaporation of a small number of samples as opposed to slow evaporation of a large number of samples as offered by centrifugal evaporators. By way of illustration, a typical application for evaporation might be the separation of 50 mg of solid from 30 ml of a solution of 50:50 (by volume) of water and Acetonitrile, for which the best centrifugal evaporators currently available would typically take about 16 hours to complete the evaporation and could dry 16 such samples in parallel. Centrifugal evaporators of this type are also relatively inconvenient to load/unload. 
         [0006]    Another feature of centrifugal evaporators of this type is that they concentrate or dry the solutions in the receptacle in which the solution was presented to the system, and thus cannot concentrate a volume of solution that is larger than the vial of choice into that vial. Centrifugal evaporators of this type are further limited in that when solutions are dried into solids, the solids take the form of hard pellets in the bottom of the receptacle. It is not only difficult to evaporate the final molecules of solvent from these pellets but the pellets themselves are very difficult to redissolve. 
         [0007]    An object of the invention is to further develop the apparatus and method of the kind described to provide an evaporation system capable of concentrating a solution that is contained in one receptacle, a round bottomed flask for example, into a receptacle of a form more suitable for storage and transportation, a screw cap vial for example. It is also an object of this invention to provide an apparatus and method that accomplishes the above objective in a manner so that it is easier and requires less laboratory staff and/or time to complete the concentration process. 
         [0008]    It is a further object of this invention to provide an apparatus and method that reduces or eliminates the disadvantages of the prior art evaporators discussed above. 
       SUMMARY OF THE INVENTION 
       [0009]    Therefore at its most general, the present invention provides an apparatus and method for concentrating and/or drying solutions in a receptacle which involves evaporation under low pressures whilst the receptacle is being rotated at high speed in a substantially vertical orientation. 
         [0010]    The high speed rotation allows the surface area of the solution in the receptacle to be maximised whilst using a standard sized/shaped receptacle, and is preferably also sufficient to prevent bumping. The vertical orientation of the receptacle also contributes to maximising the surface area, whilst allowing easy exchange of receptacles. 
         [0011]    According to a first aspect of the present invention there is provided an apparatus for concentrating solutions in a vaporising receptacle, said receptacle having a mouth for the removal of vapour, the apparatus comprising:
       support means for supporting the vaporising receptacle with the mouth of the receptacle facing upwards;   rotation means being operable to rotate the vaporising receptacle thus supported at high speed about a substantially vertical rotation axis;   a vacuum pump to reduce the pressure within the vaporising receptacle;   and means for sealing the vaporising receptacle to the apparatus to maintain the reduced pressure.       
 
         [0016]    Preferably the apparatus also includes means for dispensing a solution to be concentrated into the vaporising receptacle. 
         [0017]    Preferably the apparatus also includes sensing means to measure the temperature of the solution within the vaporising receptacle; and heating means to apply heat to the solution within the vaporising receptacle. 
         [0018]    Preferably the heating means includes a hot air heater arranged to direct hot air flow onto the receptacle. The heating means may also include a diverter for controlling the direction of the hot air flow and in one position directing said flow away from the receptacle. 
         [0019]    Preferably the apparatus also includes a control and regulating unit for controlling or regulating at least one of said rotation means, said vacuum pump, said dispensing means, said sensing means and said heating means. 
         [0020]    Preferably the vaporising receptacle is rotated (and the rotation means is operable to rotate the receptacle) at a speed sufficient to prevent the solution from bumping when heat is applied to the contents at a pressure below atmospheric conditions. 
         [0021]    More preferably the rotation means is operable to rotate the vaporising receptacle to speeds at which centrifugal force flattens the solution against the side walls of the receptacle. 
         [0022]    Preferably the rotation means is operable to rotate the vaporising receptacle at speeds of 2000 rpm or higher, and more preferably the rotation means is operable to rotate the vaporising receptacle at speeds of 3250 rpm or higher, and ideally at speeds of 6000 rpm or higher. 
         [0023]    Preferably the apparatus further comprises a removable vaporising receptacle. Conveniently the removable vaporising receptacle is a standard clear glass vial of substantially cylindrical shape. Preferably the vial has one closed end, the other end having an axially located aperture (mouth) of a diameter smaller than that of the cylinder. For example, the receptacle may be a 20 ml scintillation vial. 
         [0024]    Thus the apparatus of the present invention can be used with standard vials, and there is no need to transfer the concentrated solution or the dried solute from the receptacle to a further receptacle for transport or storage. 
         [0025]    Preferably the mouth, through which the solution be concentrated is dispensed, remains positionally stationary whilst the receptacle is rotated (albeit rotating). This can be achieved by arranging the apparatus and the receptacle such that the rotational axis passes through the mouth of the receptacle. Thus the sealing means of the apparatus may also remain positionally stationary, facilitating introduction and removal of the receptacle to/from the apparatus. 
         [0026]    Advantageously, the vaporising receptacle has features to enable a closure to be fixed to the open end. Such features may include a threaded portion or a return feature to enable the application of a crimp type closure. 
         [0027]    Preferably the temperature sensing means is a non-contact temperature sensor, and in particular the non-contact temperature sensing means may be a device known as an infra red pyrometer, which may be arranged to sense the temperature of the solution or dry products through the walls of the vaporising receptacle. Using a non-contact temperature sensor allows the receptacle to be rotated at high speeds without also having to consider the rotation of, or constraints on rotation resulting from, a contacting temperature sensor. 
         [0028]    For precise measurements using an infra red pyrometer it may be preferable to turn off the heating means for a period prior to accepting temperature measurements. 
         [0029]    Alternatively, a device to measure the temperature of the vapour directly may be located in the vapour flow immediately ‘down stream’ of the rotating vacuum connection or the vaporising chamber if this embodiment is adopted. Assuming that vapour is flowing, measuring the temperature of the vapour gives a good approximation to the temperature of the solution that the vapour is evaporating from. 
         [0030]    The heating means may be a source of infra red radiation. Alternatively, the heating means may be a hot air blower employed to direct hot air onto the outside of the vaporising receptacle. 
         [0031]    Preferably, during the evaporation process, the vaporising receptacle is sealed by pressing the open aperture against a seal that is itself connected to a rotating vacuum connection. This rotating vacuum connection facilitates the connection to the vacuum pump. 
         [0032]    Alternatively, the vial may be contained within a sealed vaporising chamber with a connection between this vaporising chamber and the vacuum pump. 
         [0033]    The apparatus may further comprise means for engaging and disengaging a vaporising receptacle with the apparatus. This means for engaging and disengaging may be manually or automatically operated. This means may also provide for simple or automated replacement of the receptacle with a further (e.g. empty) receptacle. 
         [0034]    To further enhance the degree of automation of the dispensing operation a level sensing means may be employed to detect the level of the solution within the vaporising receptacle. 
         [0035]    Preferably the level sensing means is used to detect the level of the solution only when the vaporising receptacle is substantially stationary. 
         [0036]    The level sensing means may be a non-contacting optical device. 
         [0037]    Alternatively, the level sensing means may be a contact sensing device employing the know principle of measuring changes in conductivity to detect the surface of the solution. 
         [0038]    To enable the evaporator to collect the discharged solvent it is advantageous to connect a condenser to the exhaust of the vacuum pump in a manner known per se. 
         [0039]    Thus the solvent can be re-used as appropriate, and the emission of the apparatus controlled. 
         [0040]    To maximise the evaporation performance, particularly when concentrating solutions that contain solvents having high boiling points, it is advantageous to connect a condenser in the conduit between said vaporising chamber or rotary vacuum connection and said vacuum pump. 
         [0041]    Preferably there are two condensers, a first condenser being located between the vaporising receptacle and the vacuum pump and a second condenser being connected to the exhaust of the vacuum pump. 
         [0042]    The control unit may be employed to ensure that the condition of at least one, and preferably all, of the following parameters within the vaporising receptacle is acceptable prior to dispensing a quantity of the solution: pressure, temperature and rotational speed. 
         [0043]    Additionally, the control unit may be employed to ensure the rotational speed of the vaporising receptacle is acceptable prior to reducing, to a level below atmospheric conditions, the pressure in the vaporising receptacle. Thus the control unit may prevent bumping by ensuring that a sufficient rotational speed is reached before low pressure evaporation commences. 
         [0044]    To facilitate a greater degree of automation, a pressure sensing means may be inserted into the conduit between said vaporising chamber, or rotary vacuum connection, and said vacuum pump. The electrical signal from this sensing means is connected to the control and regulating unit. 
         [0045]    To further enhance the degree of automation, a solenoid actuated valve may be placed into the conduit between said vaporising chamber or rotary vacuum connection and said vacuum pump to provide a means of controlling the pressure in said receptacle. 
         [0046]    Preferably the valve employed before the vacuum pump is of the two port two position, normally closed type. 
         [0047]    To still further enhance the degree of automation, a second solenoid actuated valve may be placed into a further conduit, said further conduit being connected into the first conduit at a location between said vaporising chamber or rotary vacuum connection and said vacuum pump. This second solenoid actuated valve may allow a rapid change of the pressure within the vaporising receptacle to atmospheric conditions. 
         [0048]    Preferably the valve employed in said further conduit is of the two port two position, normally open type. 
         [0049]    In embodiments of the invention, the apparatus may further comprise a sample loop in which the solution to be concentrated is buffered for dispensing into the vaporising receptacle. 
         [0050]    The control unit may be appropriately configured to control the flow of solution into and out of the sample loop. 
         [0051]    The apparatus may further comprising a solution pump arranged to pump the solution to be concentrated into the vaporising receptacle, and in such cases, the control unit may operate the solution pump to pump the solution to be concentrated into the vaporising receptacle substantially continuously whilst the vaporising receptacle is being rotated. 
         [0052]    The means for dispensing the solution may include a nozzle. 
         [0053]    Preferably the nozzle and the solution pump are chosen such that the solution is dispensed into the vaporising receptacle in a continuous jet. 
         [0054]    Preferably the nozzle and the solution pump are chosen such that there is a pressure difference across the nozzle of at least 1 bar. 
         [0055]    The control unit may be appropriately configured to control the dispensing (and in particular the rate of dispensing) of the solution into the receptacle whilst rotation and evaporation are occurring. The control unit may also be configured to detect when the capacity of the receptacle for concentrated solution or dry solute is reached and interrupt the continuous dispensing. Optionally the control unit may be further configured to automatically replace the receptacle when the capacity is reached and recommence the continuous evaporation process. 
         [0056]    A further aspect of the present invention provides an apparatus for producing concentrated solutions or dry solvate including a first apparatus according to the first aspect above (which may have any combination of the preferred and optional features of the above aspect) and a second apparatus for performing a precursor process which supplies a solution to be concentrated to said first apparatus. 
         [0057]    The precursor process may be any one of: high performance liquid chromatography, purification of organic compounds by flash chromatography, purification of organic compounds by preparative scale supercritical fluid chromatography or synthesis of organic compounds using continuous flow techniques. 
         [0058]    Heating of the rotating vacuum connection (or the vaporising chamber, if this embodiment is adopted), may be required when evaporating some solvents to prevent condensation. 
         [0059]    Where it is necessary to limit the maximum temperature of the concentrated sample then the heating means may be such that its heat output is controlled by the magnitude of an electrical current, and current controlling means is provided adapted to control the said electric current to the heating means, and the signal from the temperature sensing means is employed to control the current controlling means and thereby the heat output from the heating means and in turn the temperature to which the concentrated sample is permitted to rise. 
         [0060]    Preferably, the dispensing means is comprised of a conduit to feed the solution from the feed receptacle, a valve to regulate the flow of solution and a further conduit to feed the solution into the vaporising receptacle. 
         [0061]    Preferably the valve employed in the dispensing means is of the two port two position normally closed type. 
         [0062]    Alternatively, the dispensing means may be comprised of a conduit to feed the solution from the feed receptacle, a volumetric pump to feed a measured quantity of solution, a valve to seal the pump and conduit from the vaporising receptacle and a further conduit to feed the solution into the vaporising receptacle. 
         [0063]    A further alternative, the dispensing means may be comprised of a pipette and syringe pump arrangement in a manner known per se. To facilitate this arrangement, the vaporising receptacle may be moved either manually or by automated means to a position clear of the rotating vacuum connection giving the pipette access to dispense a measured quantity of solution into the receptacle. 
         [0064]    Where the volume of solution to be concentrated is greater than the capacity of a single vaporising receptacle the dispensing means can be used in conjunction with the apparatus to complete a series of automated dispense and concentrate cycles. By this process a total volume of solution many times greater than the volume of the vaporising receptacle can be concentrated into a single vaporising receptacle. For example the contents of a 250 ml round bottom flask may be either concentrated or dried completely into a single 20 ml scintillation vial. 
         [0065]    In a development of the above aspects, the receptacle may be supported to rotate about an axis that is at an angle to the longitudinal axis of the vaporising receptacle itself. In this configuration the aperture is arranged to run true while the closed end is arranged to rotate in an eccentric matter. An advantage of this arrangement is that the solids dried from solution are deposited predominately at a location close to the closed end of the vaporising receptacle. Preferably the angle between the rotational axis and the longitudinal axis of the vaporising receptacle is between 0 and 6 degrees. 
         [0066]    According to a further aspect of the invention, there is provided an apparatus for concentrating solvents, the apparatus comprising, a removable vaporising receptacle supported by a rotation means being operable to rotate the vaporising receptacle substantially about its axis, a means for sealing the vaporising receptacle, a vacuum pump to reduce the pressure within the vaporising receptacle, a means for dispensing into the vaporising receptacle a solution to be concentrated, a non-contacting sensing means to measure the temperature of the solution within the vaporising receptacle, a heating means to apply heat to the solution within the vaporising receptacle, a control and regulating unit for controlling or regulating at least one of, said rotation means, said vacuum pump, said dispensing means, said sensing means, said heating means, and said condensing means. 
         [0067]    The apparatus of this aspect may include any combination of the preferred or optional features of the above aspects. 
         [0068]    A further aspect of the present invention provides a method of concentrating a solution comprising the steps of:
       dispensing said solution into a vaporising receptacle, the receptacle having a mouth for the removal of vapour;   supporting said vaporising receptacle with the mouth facing upwards;   rotating the thus supported vaporising receptacle at high speed about a substantially vertical rotational axis;   reducing the pressure in said vaporising receptacle to evaporate at least a portion of the solvent.       
 
         [0073]    Preferably the method also includes the step of maintaining the temperature of said vaporising receptacle within a predetermined range until a portion of the solvent has evaporated. 
         [0074]    Preferably the vaporising receptacle is rotated at a speed sufficient to prevent the solution from bumping when heat is applied to the contents at a pressure below atmospheric conditions. 
         [0075]    Preferably the vaporising receptacle is rotated at speeds sufficient for centrifugal force to flatten the solution against the side walls of the receptacle. 
         [0076]    Preferably the vaporising receptacle is rotated at speeds of 2000 rpm or higher, more preferably at speeds of 3250 rpm or higher, and ideally at speeds of 6000 rpm or higher. 
         [0077]    The step of maintaining the temperature may include controlling a hot-air heater which is arranged to direct air flow onto the vaporising receptacle. This step may further include controlling a diverter mechanism which allows the air flow from the hot-air heater to be directed onto or away from the vaporising receptacle. 
         [0078]    The step of rotating the receptacle at high speed may be commenced before or after the solution has been dispensed into said receptacle. 
         [0079]    The step of maintaining the temperature of receptacle may include sensing the temperature of the receptacle with a non-contact temperature sensor. 
         [0080]    The receptacle used preferably has a mouth at one end through which the solution is dispensed into the receptacle and evaporated solvent is withdrawn from the receptacle, the rotation of the receptacle being such that said aperture remains substantially positionally stationary when the receptacle is rotated. This can be achieved by having the rotational axis pass through the mouth. 
         [0081]    In embodiments of the present aspect, the receptacle is substantially rotationally symmetric about a longitudinal axis, and the rotational axis is titled relative to that longitudinal axis. If these axes are tilted relative to each other, the angle of tilt is preferably between 0 and 6 degrees. 
         [0082]    In a development of the present aspect, the step of dispensing is performed substantially continuously throughout the concentration process. 
         [0083]    In this development, the method may further comprise the step of controlling either the rate at which the solution is dispensed into the vaporising receptacle, or the rate at which solvent is evaporated in said receptacle, such that a uniform film of solution is maintained over the side walls of the receptacle. 
         [0084]    In one arrangement the step of controlling includes sensing the temperature of two different portions of the receptacle, a first of said portions being an area of the receptacle proximate to the impact area of a heat source maintaining the temperature of the receptacle, and a second of said portions being an area of the receptacle which is distant from the impact area of said heat source, and adjusting either of said rates according to the rate of change in the difference between the two sensed temperatures. 
         [0085]    Alternatively or additionally in this development, the method may further comprise the step of controlling the pressure in the receptacle to prevent phase change from liquid to solid as the solution is dispensed. 
         [0086]    Preferably in this development the dispensed solution is supplied under pressure, more preferably at a pressure of at least 4 bar. 
         [0087]    Preferably in this development the solution is dispensed into the vaporising receptacle through a nozzle, and more preferably the nozzle and flow rate are selected and/or controlled such that there is a pressure difference of at least 1 bar across said nozzle. 
         [0088]    In another development of this aspect, the method further includes the step of storing the solution to be concentrated in a sample loop prior to dispensing said solution into said receptacle. 
         [0089]    In either of the above developments said solution may be provided to said receptacle or said sample loop directly from a preceding process. 
         [0090]    Said preceding process may be one of: high performance liquid chromatography; purification of organic compounds by flash chromatography; purification of organic compounds by preparative scale supercritical fluid chromatography; or synthesis of organic compounds by continuous flow techniques. 
         [0091]    The method of the present aspect is preferably performed using an apparatus according to any one of the preceding aspects, and the method may include further optional or preferred features which correspond to any combination of the optional or preferred features of the preceding aspects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0092]    Examples of solvent evaporators in accordance with the invention are now described with reference to the accompanying drawings in which: 
           [0093]      FIG. 1  shows the features of a removable vaporising receptacle. 
           [0094]      FIG. 2  shows a schematic, not to scale, sectional view of a first embodiment of the invention incorporating a rotating vacuum connection. 
           [0095]      FIG. 3  shows a detailed sectional view of the rotating vacuum connection of  FIG. 2 . 
           [0096]      FIG. 4  shows a schematic, not to scale, sectional view of a second embodiment of the invention incorporating a vaporising chamber in place of the rotating vacuum connection. 
           [0097]      FIG. 5  is a detailed sectional view showing the location for the vaporising receptacle with respect to its axis of rotation. 
           [0098]      FIG. 6  shows a control schematic. 
           [0099]      FIG. 7  shows a detailed sectional view of a heating apparatus as used in embodiments of the invention. 
           [0100]      FIG. 8  shows a schematic, not to scale, sectional view of a third embodiment of the invention in which the solution is fed to the evaporator via a sample loop. 
           [0101]      FIG. 8B  shows a schematic view of the valve of  FIG. 8  in the “load” position. 
           [0102]      FIG. 9  shows a schematic, not to scale, sectional view of a fourth embodiment of the invention in which the solution is fed to the evaporator from a pumped source. 
           [0103]      FIG. 10  shows a detailed sectional view of part of a fifth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0104]    With reference to  FIG. 1 , a vaporising receptacle  1  has a substantially cylindrical portion  4  the axis of this cylindrical portion is labelled  5 . The receptacle is closed at the lower end  2 . An aperture  3  in the upper end is concentric with the cylindrical portion  4 , having a diameter smaller than the internal diameter of the cylindrical portion  4 . A feature  6  is provided for fixing a closure by, for example, manual operation, to the receptacle once the evaporation process is complete. The vaporising receptacle is manufactured from an impervious inert material so that it will not contaminate the sample or suffer corrosion; the material also allows transmission of infrared radiation. A suitable vaporising receptacle is readily available, being a 20 ml scintillation vial manufactured from borosilicate glass material. 
         [0105]    Referring to  FIGS. 2 and 6 , in the embodiment shown in  FIG. 2 , the vaporising receptacle  1  is supported on the end of a shaft  7 , which is mounted for rotation about its axis in bearings  78  and  79 , drive for which is provided by an electric motor  89 . The bearings  78  and  79  and motor  89  are connected to housing  8  which is rigidly connected to carriage  9 , which is mounted using a pair of linear sliding bearings (not shown) to slide along a pair of shafts indicated by  10 . Rigidly attached to the lower end of shaft  10  is a block  17 . At least one compression spring is constrained to slide along shaft  10 , being constrained between block  17  and carriage  9 , thereby capable of exerting an upwards force onto carriage  9  resisting downward movement. A user operable leaver  14  is pivotally mounted onto block  18  by pin  62 , a further pin  15  is rigidly mounted into carriage  9  and is constrained to run within a slot in lever  14 . Block  18  is rigidly mounted to shafts  10 . By the constraints described, a downward movement of lever  14  will produce a downward movement of carriage  9  and thereby, receptacle  1  relative to the fixed shafts  10 . 
         [0106]    When no force is applied to lever  14 , by the action of spring  16  the upper portion of bottle  1  is forced into contact with the elastomeric seal  13 . The sealing material is an impervious inert material so that it will not contaminate the sample or suffer degradation when exposed to solvents, a perfluorinated elastomer is suitable, and examples of brand names are Isolast™ and Kalrez™. Seal  13  is constrained by the rotating vacuum connection against vertical or lateral movement but is allowed to rotate freely about the vertical axis. 
         [0107]    Referring to  FIG. 3  showing a detailed sectional view of the rotating vacuum connection, seal  13  is located into a groove in shaft  52 , which is mounted for rotation in bearings  54  and  55 . A port  53  is provided running through the entire length of shaft  52  connecting the internal volume of vaporising receptacle  1  to the chamber  80  within the housing  56 . The bearings  54  and  55  are mounted within housing  56  which is rigidly mounted to block  12 , which is rigidly mounted to the upper portions of shafts  10 . A sealing cap  58  is clamped to the top of body  56  by screws  60  and  61 , an elastomeric seal  59  prevents leakage of air through the joint between cap  58  and body  56  into chamber  80 . A shaft seal  57  is rigidly mounted within housing  56  to prevent leakage of air into chamber  80  between the housing  56  and the shaft  52 . The sealing material is an impervious inert material so that it will not contaminate the sample or suffer degradation when exposed to solvents, a polytetraflouroethylene (PTFE) based seal material is suitable, a brand name is Turcon™. 
         [0108]    Referring now to  FIGS. 1 ,  2 , 3  and  6 , a tube  22 , welded into cap  58  passes completely through the port  53  projecting below the lower end of shaft  52  into the internal volume of the vaporising receptacle  1 . A resistive heating device  40  and a temperature sensing device  41  are connected by a means providing good thermal contact to the outer surface of the rotary vacuum connection  11 , for the purpose of heating the rotary vacuum connection  11  to a temperature determined by the control system  75 . The port  32  in cap  58  is connected via conduits  33 ,  38 ,  44  and  69  to a vacuum pump  46 , provided for the purpose of reducing the pressure within the vaporising receptacle causing the solvents contained within to boil at a maximum temperature that will not cause degradation to components contained within the solution, as such components are often thermo-labile. Typically for development of pharmaceutical drug compounds this upper temperature limit would be 37 degrees Celsius. The conduits  29  and  30  connected to tube  22  are in turn connected to isolating valves  27  and  28 , each valve is connected a single solution supply vessel, valve  27  connected to solution supply vessel  63  by conduit  26  and valve  28  connected to solution supply vessel  64  by conduit  25 . 
         [0109]    A source of infra red radiation  19  is arranged to focus infra red radiation through the cylindrical portion  4  of the vaporising receptacle  1  for absorption by the solution within the chamber  1 . A suitable source of infra red radiation is a tungsten halogen lamp with gold plated parabolic reflector. Additional reflectors, not shown, are arranged to reflect transmitted radiation back into the solution and away from the shaft  7 , housing  8 , seal  13 , shaft  52  and housing  11 . At a location, at an angle to the direct path of the infra red radiation, an infra red pyrometer  21  is arranged to measure the temperature of the solution within the vaporising receptacle  1 . At a further location, not in direct path of the infra red radiation, an optical liquid sensing device  20  is arranged to detect when the level of the solution within the vaporising receptacle  1 , when vaporising receptacle  1  is stationary, is at or above the level at which the optical sensing device is set to monitor. The level at which the optical sensing device is set to monitor can be adjusted by the user of the apparatus by a slider with pinch screw means, not shown. 
         [0110]    Connected between conduit  33  and conduit  38  is a vapour temperature sensing device  34 . Attached to the sealed housing  90  is a resistive heating device  36  and a temperature sensing device  37  connected by a means providing good thermal contact to the outer surface of housing  90 , for the purpose of heating the housing  90  to a temperature determined by the control system  75 . A temperature sensing device  35 , a thermocouple, is thermally but not electrically connected to a heat transfer device  81  which is mounted within the vapour flow and exchanges heat, by conduction, with the vapour. By this means the temperature sensing device  35  gives an electrical signal proportional to the temperature of the vapour within the housing  90 . The temperature sensing device is protected from the solvent vapours present within the housing  90  by means of a polytetraflouroethylene (PTFE) sheath, not shown. Signal wires  84  connecting the temperature sensing device with the control system  75 , pass through the housing  90  through a leak-free connector means. 
         [0111]    Connected into conduit  38  via conduit  83  is a pressure sensing device  39  for generating an electrical signal proportional to the pressure within the conduit  38 . The pressure sensing device  39  is connected to the control system  75  by connection lines  85 . 
         [0112]    Connected into conduit  38  via conduit  82  is a shut off valve  50 , used for venting air at atmospheric conditions drawn through conduit  51  into conduit  38 . To ensure failsafe operation of the apparatus, valve  50  is of the two port two position, normally open variety. 
         [0113]    A condenser  42 , chilled by means of external power source may be incorporated into the apparatus between conduits  38  and  44 . The purpose of the condenser  42  it to condense a proportion of solvent vapour, reducing the volume flow rate of vapour that must be pumped from the system by the vacuum pump  46 . To promote condensation of the vapour within the condenser, the temperature of the condenser  42  is maintained at a temperature below the temperature of the solution evaporating within the vaporising receptacle  1 , this is achieved by feeding a mixture of chilled water and ethylene glycol through the jacket surrounding the condensed solvent  43  by a device known as a chiller, not shown. 
         [0114]    Between conduit  44  and conduit  69  a shut off valve  45  may be advantageously incorporated for isolating the vacuum pump  46  from the apparatus providing the means to control the pressure within the apparatus to a pre-determined level. To ensure failsafe operation of the apparatus, valve  45  is of the two port two position, normally closed variety. 
         [0115]    The solvent resistant vacuum pump  46  is connected into conduit  69 , the exhaust from the pump is connected into condenser  47 . The purpose of the condenser  47  is to trap the solvent exhausted by the vacuum pump  46 , reducing the potential for atmospheric pollution or explosive ignition of the exhaust vapours. Gases and some vapour exhausted from the condenser  47  pass through conduit  49  for connection into a fume cupboard or similar means, not shown. 
         [0116]      FIG. 5  shows an embodiment in which the vaporising receptacle is inclined with respect to the axis of rotation. The axis  72  is the axis of rotation for shaft  7 , the axis  73  is the axis of rotation for shaft  52 , and the axis  5 , as previously described, is the axis of the cylindrical portion of the vaporising receptacle  1 . The axis  73  rotates substantially concentrically relative to axis  72 , with an angle  70  between axis  72  and axis  5 . The surface  71  of the solution is the position of the surface when the shaft  7  is rotating at the desired operational speed and before the volume of the solution has been reduced significantly by evaporation. The surface  74  is the position of the surface when the shaft  7  is rotating at the desired operational speed and when all the solvent has evaporated from the solution leaving a dry residue. The position and shape of the dry residue can be modified significantly by changing the angle  70 . Best results are achieved when the angle  70  is between zero and six degrees, yet it is possible for the apparatus to function at angles between zero and 45 degrees. 
         [0117]    Referring to  FIG. 4 , an alternative embodiment is described featuring a vaporising chamber  67  in place of the rotary vacuum connection  11 . The vaporising chamber  67  differs from the rotary vacuum connection  11  in that the vaporising chamber  67  does not rotate, when the lever  14  is released, the seal  66  is clamped between the vaporising chamber  67  and the base plate  86 , a shaft seal  68  is now incorporated between the base plate  86  and the shaft  7  and the vaporising receptacle is located and retained in a collet  65  attached to the upper end of shaft  7 . The walls of the vaporising chamber are manufactured from an impervious inert material so that it will not contaminate the sample or suffer corrosion; the material also allows transmission of infrared radiation. Suitable materials are borosilicate glass or quartz. Aside from the structural differences described, operation of this embodiment incorporating the vaporising chamber is identical to that for the embodiment which incorporates the rotating vacuum connection as described by  FIG. 2 . 
         [0118]    The operation of the apparatus according to the invention will now be described by reference to  FIGS. 2 and 6 . A similar method of operation applies to the embodiment of  FIG. 4  and many of the steps and features are shared with the methods of operation of later embodiments. 
         [0119]    At the start of the evaporation process, the valve  50  is in the open position venting, to atmosphere, conduit  38  and the internal volume connected to it, valve  45  is in the closed position disconnecting the vacuum pump from conduit  44  and the internal volume connected to it, and the vacuum pump  46  is powered and evacuating the conduit  69 . Isolating valves  27  and  28  are in the closed position disconnecting the solution supply vessels from the conduit  22 , the motor  89  and shaft  7  are stationary, and the infra red lamp  19  is de-energised. The maximum acceptable temperature for the solution is selected using the user interface  87 , this data is transmitted to the control system  75 , the rotating vacuum connection  11  is heated to the maximum allowable solution temperature by the action of heater  40  and controlled/detected by temperature sensor  41 . The housing  90  is also heated to the maximum allowable solution temperature by the action of heater  36  and temperature sensor  37 . One or more solution supply vessels are placed at locations indicated by  63  and  64 . The lever  14  is moved in a downward direction and an empty vaporising receptacle  1  is placed onto the shaft  7 . The lever  14  is then eased in an upward direction under the action of spring  16  and the vaporising receptacle  1  is forced against the seal  13  thus connecting, without leakage, the vaporising receptacle  1  to the rotating vacuum connection  11 . 
         [0120]    The apparatus is now ready to commence the remainder of the evaporation processes in an automated manner, the start button is activated on the user interface  87 , and this data is transmitted to the control system  75 , stage A is initiated. 
         [0121]    In stage A, the valve  45  is energised, connecting the vacuum pump and conduit  69  to conduit  44 , the pressure is reduced throughout the connected conduits, and also within the vaporising receptacle  1 . Valve  50  remains open, and thus air at atmospheric conditions flows through conduit  51  into conduit  38 , in this manner the pressure within the vaporising receptacle  1  is regulated, being governed by the flow restriction inherent in the geometry of conduit  51 . A pressure of approximately 100 mbar below the atmospheric conditions is suitable. With the pressure within the vaporising receptacle  1  at a pressure below atmospheric, the magnitude of the pressure is confirmed by pressure sensor  39 , the temperature of the vaporising receptacle  1  is measured using the infra red pyrometer  21 , if both pressure and temperature are within acceptable limits, stage B is initiated. 
         [0122]    In stage B, valve  28  is opened, the pressure difference between the port  22  and the solution  24  causes the solution  24  to be forced through valve  28 , conduit  30  and conduit  22  into the vaporising receptacle  1 . When the level sensor  20  detects the required level of solution in the vaporising receptacle  1 , valve  28  is closed, stage C is initiated. If the required level is not achieved then it is assumed that vessel  64  is empty, in this case, valve  28  is closed and valve  27  is opened, the process continues. If the required level is not achieved when valve  27  is open then it is assumed that all solution supply vessels are empty, and stage E is initiated. 
         [0123]    In stage C, the motor controller  76  ramps the motor up to full speed, the tachometer sensor feeds the motor speed back to the control system  75 , and when full motor speed is achieved, valve  50  is closed and the pressure in the vaporising receptacle reduces rapidly. The minimum operational rotational speed for shaft  7  is defined as that speed sufficient to prevent the solution from bumping and foaming when heat is applied to the contents at a pressure at or below the saturated vapour pressure of the solution within the vaporising receptacle  1 . It has been found, by experiment, that a speed in excess of that necessary to subject the solution to an acceleration of 150 times the normal gravitational attraction is required. For example, if the vaporising receptacle  1  is a 20 ml scintillation vial then a minimum speed of 3250 RPM is required, if the vessel is a 4 ml HPLC vial a speed of 6000 RPM is required. The temperature of the vapour, determined by sensor  35 , is monitored continuously, a control algorithm within the control system  75  uses the vapour temperature data from sensor  35  to control the average power supplied to the infra-red lamp  19  to maintain the vapour temperature as measured by sensor  35  to a target value which is slightly lower than the maximum acceptable temperature as set using the user interface  87 . Once the target value of vapour temperature is achieved together with the average power supplied to the infrared lamp  19  having decreased below a predetermined lower threshold level, the control system  75  assumes the majority of the solvent has evaporated from the solution, and stage D is initiated. 
         [0124]    In stage D, the valve  45  is moved to a closed position disconnecting the vacuum pump from conduit  44  and the internal volume connected to it, the valve  50  is moved to an open position venting, to atmosphere, conduit  38  and the internal volume connected to it. Once the pressure in conduit  38 , measured by pressure sensing device  39  has increased to a level above a predefined minimum value, the speed of motor  89  is ramped down to stop. When a motor stationary condition is measured by the tachometer  77 , stage B is initiated once again. Stages B to D inclusive are repeated until all the solution contained within the solution supply vessels  63  and  64  has been transferred to the vaporising receptacle  1  and evaporated. 
         [0125]    In stage E, the motor controller  76  ramps the motor  89  up to operational speed, the tacho sensor feeds motor speed back to the control system  75 , when the minimum operational rotational speed for shaft  7  is achieved, valve  50  is closed and the pressure in the vaporising receptacle reduces rapidly. The temperature of the contents within the vaporising receptacle  1 , determined by the non-contact temperature sensor  21 , is monitored continuously, and a further control algorithm within the control system  75  uses the temperature data from sensor  21  to control the average power supplied to the infra-red lamp  19  to maintain the temperature as measured by sensor  21  to a target value which is slightly lower than the maximum acceptable temperature as set using the user interface  87 . Prior to taking each temperature measurement with the non-contact temperature sensor  21 , the control system  75  ensures that the infra-red lamp  19  has been off for a pre-determined period of time. Once the average power supplied to the infrared lamp has decreased below a predetermined lower threshold level, the temperature as measured by the non-contact temperature sensor  21  is maintained at the maximum acceptable temperature, and the control system  75  starts a timer for the final drying period. Once the final drying period has been completed, the control system assumes that the product contained within the vaporising receptacle is dry, and stage F is initiated. 
         [0126]    In stage F, the valve  45  is moved to a closed position disconnecting the vacuum pump from conduit  44  and the internal volume connected to it, the valve  50  is moved to an open position venting, to atmosphere, conduit  38  and the internal volume connected to it. Once the pressure in conduit  38 , measured by pressure sensing device  39  has increased to a level above a predefined minimum value, the speed of motor  21  is ramped down to stop. When the motor stationary condition is measured by the tachometer  77 , the evaporation process is complete, the control system  75  indicates this via a lamp on the user interface  87 . 
         [0127]    The empty solution supply vessels  63  and  64  are removed, the lever  14  is moved in a downward direction and the vaporising receptacle  1  containing the concentrated solution is removed from shaft  7 , if necessary, the pump is turned off and the trapped solvent is removed from the two condensers  42  and  47  for disposal. 
         [0128]      FIG. 7  shows an alternative apparatus and method for heating the contents of the vaporising receptacle  1 , using a hot air heater  99  instead of infra-red lamp  19 , which may be used in conjunction with embodiments of the present invention. 
         [0129]    A two stage axial fan  91  draws air at room temperature and forces the air past the resistive heating elements  94 . A suitable fan is manufactured by Sanyo Denki and provides airflow 0.4 m 3 /min at a static pressure of 300 Pa. The heating element is mounted inside a thin walled tube  92  of low thermal conductivity. Stainless steel and titanium are both suitable materials for this tube. The heating element is electrically and thermally isolated from the thin walled tube  92  by a sleeve  93  of insulating material. A suitable material for this sleeve is Filamic tube FT19 supplied by Langtec Mica Ltd. A temperature sensing device  95 , such as a thermister, positioned in the airflow as it exits the heating element, is used to measure the temperature of the air. 
         [0130]    A butterfly valve  97  is positioned between the vaporising receptacle  1  and the temperature sensor  95 , and can be actuated to one of two positions, either to allow the hot air to heat the vaporising receptacle  1  or to divert the hot air out of the system through exit tube  98 . The butterfly valve  97  is actuated by a solenoid, not shown, although alternatively a pneumatic cylinder could be used to actuate the butterfly valve  97 . Preferably the butterfly valve  97  is sprung to return the valve to the divert position where air is diverted through tube  98 . Between the butterfly valve and the vaporising receptacle  1 , the air passes through a nozzle  96 . This nozzle  96  can be easily removed and replaced and the size of the nozzle  96  can be chosen to suit the size of the vaporising receptacle  1 . 
         [0131]    At the start of the evaporation process the fan  91  is powered, the heating element  94  is disconnected from the electrical supply and the butterfly valve is in the divert position. The vaporising receptacle  1  is rotated and the vacuum pump  46  is used to reduce the pressure in the vaporising receptacle sufficiently to cause the solvent within the vaporising receptacle  1  to boil, as described in more detail in other embodiments. The evaporation of the solvent within the vaporising receptacle  1  results in a rapid reduction of temperature of the vaporising receptacle, which is measured by the non-contact temperature sensor (e.g. an infra-red pyrometer)  21 . In response to this reduction in temperature, the butterfly valve is activated allowing air to flow from the fan  91  to the vaporising receptacle  1 . At the same time a control loop is enabled in which the heater power is adjusted to achieve and maintain a target temperature of the vaporising receptacle  1  as measured by the non-contact temperature sensor  21 . The control loop utilises proportional, integral and derivative terms (commonly known as PID control) to ensure both rapid response and accurate temperature control. This control is maintained until the sample is dry. 
         [0132]    If at any time during the process the temperature of the vaporising receptacle  1  exceeds the target temperature by a pre-set value then the power to the heater  94  is immediately switched off and at the same time the butterfly valve  97  is returned to the divert position. The pre-set value would typically be 3° C. above the target temperature. It is most likely that the target temperature will be exceeded by the pre-set value once most of the solvent has evaporated and the demand for heat is dramatically reduced. The butterfly valve  97  is maintained in the divert position until the air temperature, as measured by the sensor  95 , has reduced to a value lower that the target temperature. Once this condition is achieved, the butterfly valve is activated allowing air to flow from the fan  91  to the vaporising receptacle  1  and the control loop between the temperature sensor  21  and the heater  94  is re-enabled. 
         [0133]      FIG. 8  shows an apparatus according to a third embodiment of the invention. The apparatus of  FIG. 8  is similar to that shown in  FIG. 2  and corresponding items are given the same references. 
         [0134]    The apparatus of  FIG. 8  has the following differences from that of  FIG. 2 . The vacuum pump  46  is driven using a variable speed drive which enables control of the pressure within the vaporising receptacle  1  without the valve  45 . No vapour temperature sensor  90  is used. The vaporising receptacle  1  is supported on the end of shaft  7  which is in turn supported by a motorised lifting mechanism  109 . At the uppermost end of tube  22  is connected a 5 port rotary valve  103 . This valve  103  allows the volume within the vaporising receptacle  1  to be connected to either: a nitrogen supply  101  via a two port normally closed valve  102 ; to a blanked off port  116 ; to a further valve  104 ; or to connect the valve  104  directly to the waste container  100 . 
         [0135]    The six port rotary valve  104  is known within the industry as an injection valve. Connected to one port of the rotary valve  104  is a syringe pump  106 , with a further 3 port distribution valve  107 . A sample loop  105  of sufficient capacity to accommodate the whole of the solution containing the sample of interest is connected across two of the ports in a manner commonly used within the industry. The solution to be evaporated is supplied from a preceding process to the port labelled ‘2’ of the valve  104 . 
         [0136]    Examples of preceding processes which may be used with the present embodiment include: purification of organic compounds by preparative scale High Performance Liquid Chromatography (HPLC); purification of organic compounds by Flash Chromatography; purification of organic compounds by preparative scale supercritical fluid chromatography (SFC); synthesis of organic compounds by continuous flow techniques. 
         [0137]    At the start of the evaporation process the motorised lifting mechanism  109  is in the fully lowered position, a clean vial is located onto the shaft  7 , the rotatable shaft  7  is stationary, the tube  22  and the tube connecting valve  104  to  103  have been cleaned with pure solvent, valve  103  is positioned to connect tube  22  to the blanked off port  116  (position ‘2’), valve  102  is in the closed position, and valve  104  is switched to the load position (shown in  FIG. 8B ). Thus the process is operating such that solution is flowing continually through the sample loop. The process indicates when solution to be evaporated is present within the sample loop, and also indicates the volume of this solution. 
         [0138]    Next, the valve  104  is switched to the ‘inject’ position (as shown in  FIG. 8  itself), in which the sample loop  105  is connected between the syringe pump  106  and the selection valve  103 . The motorised lifting mechanism  109  is powered, lifting the vial until it engages with the elastomeric seal  13 , and the drive motor  89  is energised to rotate the vial at high speed (in the range 3,250 to 10,000 rpm). When the required speed has been achieved the valve  103  is positioned to connect the valve  104  directly to tube  22 , and the syringe pump  106  is driven to pump pure solvent from receptacle  108  through the sample loop  105  and into the vaporising receptacle  1 , carrying the solution present within the sample loop  105  into the vaporising receptacle  1 . 
         [0139]    When either all the solution in the sample loop  105  has been dispensed into the vaporising receptacle  1 , or the capacity of the vaporising receptacle  1  has been reached, then the pump  106  is stopped, the valve  103  is switched to connect tube  22  to the nitrogen supply, the valve  102  is switched on for a short duration to eject the solution remaining within tube  22  into the vaporising receptacle  1 . The valve  103  is then moved to connect tube  22  to the blanked port  116 . 
         [0140]    The evaporation process is then initiated: the vent valve  27  is closed, the vacuum pump  46  is powered to gradually reduce the pressure in the vaporising receptacle  1 , the control loop is initiated to heat the contents of the vial in response to the feedback from the non-contact sensor  21 . When all the solvent has evaporated (which can be determined, for example, by monitoring the power required to maintain the temperature of the vaporising receptacle  1 ), then if all the solution within the sample loop  105  has been dispensed into the vaporising receptacle  1  the process can continue for a period of a few minutes to completely dry the compound, and otherwise valve  27  is opened to return the pressure within the vaporising receptacle  1  to atmospheric and a further dispense and evaporate cycle can be initiated. 
         [0141]    When the last of the solution to be evaporated within the sample loop  105  has been dispensed then a cleaning cycle is initiated. This cleaning cycle is as follows: with the vaporising receptacle  1  maintained at vacuum, if required, the valve  103  is switched to connect the sample loop  105  to the waste container  100 , the syringe pump  106  is used to pump a volume of pure solvent from the container  108  through the sample loop  105  and into waste container  100 . Typically, the volume of pure solvent would be 4 times the volume of the sample loop  105  to ensure adequate cleaning. The valve  104  is returned to the load position, the sample loop is then available to accept the next sample. The pump  106  is stopped, the vacuum pump stopped, and the valve  27  opened. When the pressure within the vaporising receptacle  1  has returned to atmospheric, the valve  103  is switched to connect tube  117  to tube  22 , the syringe pump  106  is used to pump pure solvent through pipe  22  into the vaporising receptacle  1 . 4 times the volume of tube  22  only is required. The syringe pump  106  is stopped, the valve  103  is switched to connect tube  22  to valve  102 , valve  102  is open for a short duration to clear tube  22  of remaining solvent. Valve  102  is closed, valve  103  returned to connect tube  22  to port  116 . The solvent in the vaporising receptacle  1  is then evaporated and dried fully in the manner already described above. Once the compound is fully dried the volume within the vaporising receptacle  1  is returned to atmospheric pressure, the spin motor  89  is turned off and the lift  109  returns the vaporising receptacle  1  to the load position. 
         [0142]      FIG. 9  shows an apparatus according to a further embodiment of the invention. The apparatus of  FIG. 9  is similar to that shown in  FIG. 8  but the valve  104 , the sample loop  105  and the syringe pump  106  have been replaced by an upstream process, generically indicated as  113 . This process  113  supplies a solution to be evaporated from a continuously pumped source. The flow rate of solution from process  113  is chosen to be within the capability of the evaporator and it is therefore possible to evaporate the solution continuously, subject of course to the capacity limitations of the vaporising receptacle. 
         [0143]    The continuous evaporation in this embodiment means that solution is dispensed substantially continuously (and preferably continuously) into the vaporising receptacle  1  at the same time and at approximately the same rate at which solution is evaporating from the vaporising receptacle  1 . Thus the vaporising receptacle  1  must be maintained at pressures significantly below atmospheric while the solution is being pumped into the vaporising receptacle. To enable this without either drawing solution from the up-stream process, or causing the solution to “bump” (evaporate in an explosive manner) as it enters the vaporising receptacle  1 , a nozzle  112  is located at the point where solution within the tube  22  enters the vaporising receptacle  1 . The up-stream process must supply solution under pressure. Typically a minimum working pressure of 4 bar is preferable. 
         [0144]    Two criteria influence the design of the nozzle: 1) The size of the nozzle is selected to match the flow-rate in order to create a pressure difference across the nozzle greater than 1 bar; and 2) The shape of the nozzle is selected to ensure the solution exits the nozzle as a jet not a series of drips. An example of a nozzle suitable for flow rates between 0.5 ml/minute and 2 ml/minute is 0.075 mm in diameter by 15 mm in length. A suitable material for the nozzle is fused silica tube such as that supplied by Upchurch Scientific Corp. 
         [0145]    Examples of preceding processes include: purification of organic compounds by preparative scale High Performance Liquid Chromatography (HPLC); purification of organic compounds by Flash Chromatography; purification of organic compounds by preparative scale supercritical fluid chromatography (SFC); synthesis of organic compounds by continuous flow techniques. 
         [0146]    At the start of the evaporation process the motorised lifting mechanism  109  is in the fully lowered position, a clean vial  1  is located onto the shaft  7 , the rotatable shaft  7  is stationary, the tube  22  has been cleaned with pure solvent, valve  103  is positioned to connect tube  22  to the blanked off port indicated by ‘2’, and the valve  102  is in the closed position. The up-stream process  113  indicates, for example by providing a signal to the control means, when it is about to start delivering solution. The motorised lifting mechanism  109  is powered, lifting the vial until it engages with the elastomeric seal  13 , and the drive motor  89  is energised to rotate the vial at a high speed (in the range 3,250 to 10,000 rpm). When the required speed has been achieved the valve  103  is positioned to connect the tube  22  to the up-stream process  113 . Once solution is exiting the nozzle  112  into the vaporising receptacle  1  in a jet the evaporation process is initiated. 
         [0147]    The vent valve  27  is closed, the pump is powered to gradually reduce the pressure in the vaporising receptacle  1 , the control loop is initiated to heat the contents of the vial in response to the feedback from the non-contact sensor  21 . While the solution is being dispensed, the pressure is precisely controlled to a pre-set minimum value, this minimum value depending on the characteristics of the solution being evaporated. Pressure control is advantageous as it may prevent phase change from liquid to solid as the solution exits the nozzle. Phase change can be caused either by freezing of the solution (e.g. in the case of water if the pressure is reduced below 6 mbar) or by precipitation of solids from solution as a volatile constituent ‘flashes off’. 
         [0148]    During this phase of the process it is also desired to maintain a uniform film of solution over the entire cylindrical surface of the vial. If this film is not maintained then temperature control of the compound as it dries may be compromised. 
         [0149]    Two methods for maintaining the film of solution have been developed. The first is a manual process whereby the rate of evaporation is adjusted by experiment to be a few percent slower than the rate of delivery. This process has been found to be effective where the total size of the sample is not more than 8 times the maximum capacity of the vial, but beyond this is generally not practical. 
         [0150]    The second method is an automated process and will be described in relation to the arrangement shown in  FIG. 10 . This method is suitable for a sample of any volume. 
         [0151]      FIG. 10  shows a detail of an apparatus that enables an automated method for maintaining a continuous film of solution while evaporating solutions from a continuously pumped source. The arrangement is generally as shown in and as described in relation to  FIG. 9  but the single non-contact temperature sensor  21  is replaced by two non-contact temperature sensors  114  and  115 . Preferably these sensors have a very small viewing area; an example of a suitable sensor is an infra-red sensor supplied by Raytek Corp. (part number DKUMID02LT) having a 2.4 mm diameter viewing area at 80 mm distance. Sensor  114  is positioned to view an area of the vial close to the height at which the hot air heater  99  is applying heat to the surface of the vial. The second sensor  115  is positioned to view an area at the upper end of the cylindrical portion of the vaporising receptacle  1 . The viewing area for sensor  115  is away from the area of the vaporising receptacle  1  being heated by the hot air heater  99 . 
         [0152]    If there is a continuous film present on the cylindrical surface of the vial then during evaporation, sensor  115  measures a temperature close to the temperature of the boiling solvent within the vial while sensor  114  measures the temperature of the heated surface of the vial. As an example, when evaporating a volatile solvent, sensor  115  may be measuring −5° C. while sensor  114  is measuring 20° C. If the film of solvent is allowed to reduce in thickness, e.g. due to the rate of evaporation being greater than the rate of delivery, then as the thickness of the solvent film reduces then the temperature measured by sensor  115  increases until it approaches the temperature measured by sensor  114 . Using the data from these two sensors it is possible to use the rate of change in the difference between the temperatures measured by sensors  114  and  115  to make corrections in either the rate of evaporation or in the rate of delivery of the solution into the vaporising receptacle  1 . 
         [0153]    Thus in operation, the evaporation continues until the up-stream process indicates (e.g. by providing a signal to the control means) that delivery is complete. The valve  103  is then switched to connect the up-stream process directly to waste container  100  and simultaneously connect tube  22  to valve  102 . Valve  102  is then opened for a short duration to clear the residual solution from tube  22  into vaporising receptacle. The up-stream process  113  stops dispensing. Valve  102  is closed and valve  103  is switched to connect tube  22  to the blanked off port  116 . The evaporation process then continues until all solvent has been evaporated but at this stage pressure control is not critical. Once all the solvent has been evaporated and the compound in the vaporising receptacle  1  has been dried the process is stopped as previously described. 
         [0154]    Using the embodiment illustrated in  FIG. 9  with the illustrative example discussed in relation to the prior art (the separation of 50 mg of solid from 30 ml of a solution of 50:50 (by volume) of water and Acetonitrile), this apparatus takes approximately 20 minutes start to finish for each 30 ml sample, compared to a typical period of about 16 hours to dry 16 such samples in parallel using the best centrifugal evaporators currently available. Furthermore, whilst the centrifugal evaporators of the prior art would produce 16 separate dry samples, the apparatus of the present invention can allow the samples to be consecutively or continuously dried in the same (or a smaller overall number of) vials. 
         [0155]    While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.