Abstract:
A system provides for automated control of solvent evaporation, such as may be done for solvent exchange in a solvent that contains analytes or extractants. The automated control is able to ascertain and take appropriate action when a solvent is boiling, when the extractants are free or dry of the solvent, and when there is thermal cycling of the solvent.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims benefit of priority to U.S. Provisional Application Ser. No. 60/773,880 filed Feb. 16, 2006, the disclosure of which is incorporated by reference to the same extent as though fully replicated herein. 
     
    
     BACKGROUND  
       [0002]     1. Field of the Invention  
         [0003]     The invention pertains to solvent evaporation systems and, particularly, the removal of solvent for active-controlled retention of analytes or extractants.  
         [0004]     2. Description of the Related Art  
         [0005]     Solvents are often used to retain analytes, carry the products of chemical reactions, or in such extraction processes as two-phase extractions. Processing of the solutions sometimes calls for concentration of the analytes, extractants, or reaction products by the removal of solvent. This concentration processing may cause a number of problems, such as the well-known ‘bumping’ phenomenon where the solvent erupts in a violent boiling mode. In other aspects where the evaporation is done by heating, the removal of solvent may proceed to a point where the analytes, extractants, or reaction products fall out of solution and begin to solidify. In these circumstances due care must be taken not induce thermal damage to the analytes, extractants, or reaction products. The process of solvent removal may be done by hand, but it is especially problematic to implement solvent removal in an automated system that overcomes these problems.  
         [0006]     U.S. Pat. No. 5,176,799 to Roe et al. discloses an evaporator with a solvent recovery feature An evaporation apparatus includes a vessel with an opening at the top thereof that forms an evaporation chamber to hold a liquid composition. A condenser assembly disposed above and hermetically sealed to the vessel to provide a wall defining a condensation chamber communicating with the evaporation chamber through the opening, an accumulator for receiving liquid condensed on the wall, and a drain for removing liquid received by the accumulator. A fluid drive is disposed above the condenser assembly and adapted to produce fluid flow downwardly through the condensation chamber and into contact with the liquid composition in the evaporation chamber, then upwardly into the condensation chamber. A heating mechanism heats the liquid composition in the evaporation chamber so as to cause evaporation thereof. A cooling device cools the wall so as to condense vapors thereon, where such vapors accompany the fluid flowing upwardly from the evaporation chamber.  
         [0007]     U.S. Pat. No. 4,465,554 to Glass discloses an apparatus for evaporating liquid fractions. The apparatus includes a nozzle from which a hot stream of non-reactive gas is directed onto the surface of the fraction that is to be evaporated, while the fraction and the nozzle are thermally insulated and sealed from the surrounding atmosphere. The evaporation process is governed by electronic controls.  
       SUMMARY  
       [0008]     The present instrumentalities overcome the problems outlined above and advance the art by providing an automated system and method for solvent removal.  
         [0009]     In one aspect, this is achieved by use of a multi-mode automated evaporator system for use in the concentration of fluids containing volatile analytes or other material and their subsequent solvent exchange and transfer to a vial. The system may be selected for use inline with a fluid stream, such as a chromatography process, where the system is isolated from a flowing fluid in such a way that the concentration procedure does not impair the overall flowing stream process.  
         [0010]     In another mode, the evaporator system may receive fluid directly from sample containers for concentration via positive pressure or negative pressure. The evaporator may either push or pull the fluid from the vessels to act as an automated bulk fluid concentrator. The system receives the fluid from the in-line process or container and is isolated. The fluid is then pulled into the evaporation vessel with negative pressure. Positive pressure may be added to assist in introducing the fluid to the vessel. The fluid is then concentrated in the evaporation vessel. The system will continue to receive sample until it is signaled that the fluid stream necessary for evaporation is complete. The system has liquid sensors to detect the presence of liquid so that temperature and vacuum zones are created. These zones allow the user to control the process temperature and vacuum pressure depending on where the fluid is detected. When all the fluid is collected, a final concentration and solvent exchange can be programmed. The fluid can be brought to a final volume in the same fluid or switched to another fluid. The final fluid is then transferred to a storage vial for use later. The system then undergoes a vigorous rinse process before receiving another fluid stream with out the first process affecting the next. The system utilizes feedback from data and sensors to enhance the automation of the system, the system safety, and the recovery of volatile analytes. Example applications are the concentration of analytes present in GPC Cleanup Chromatography effluent or bulk concentration of environmental samples. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows an automated evaporation system;  
         [0012]      FIG. 2  shows fluid sensors around the evaporation vessel;  
         [0013]      FIG. 3  shows an optimized placement as the off center location of negative pressure po 0 t for turbulence of the evaporating fluid and rinse solutions;  
         [0014]      FIG. 4  shows a balancing port for isolation of the solvent delivery from the evaporation process;  
         [0015]      FIG. 5  shows of the circuit and feedback for detection of failed heater element or open circuit;  
         [0016]      FIG. 6  is a flow diagram of turbulent rinsing;  
         [0017]      FIG. 7  is a graph showing the change over in temperature during solvent exchange in context of scaled average power input, system set points, and liquid temperature in a multi-solvent system undergoing fractionation under automated control over time;  
         [0018]      FIG. 8A  is a graph showing the temperature of dichloromethane (DCM) solvent in context of a PWM-based scaled average power system input under automated control;  
         [0019]      FIG. 8B  is a graph showing the temperature of ethyl acetate solvent in context of a PWM-based scaled average power system input under automated control;  
         [0020]      FIG. 8C  is a graph showing the temperature of cyclohexane solvent in context of a PWM-based scaled average power system input under automated control;  
         [0021]      FIG. 8D  is a graph showing the temperatures of ethyl acetate/Cyclohexane 1:1 solvent in context of a PWM-based scaled average power system input under automated control;  
         [0022]      FIG. 9  is a graph showing power limiting to prevent thermal cycling under automated control;  
         [0023]      FIG. 10  is a graph showing the detection of complete fluid dryness under automated control, wherein dryness is indicated by a steep drop in the required power input to maintain a given temperature, as is also evident from a derivative of average power input taken with respect to time;  
         [0024]      FIG. 11  is a graph showing analog to digital signal conversion values for boiling detection; and  
         [0025]      FIG. 12  shows a transport tube conFig.d with a flow sensor for detecting the presence or non presence of gas, fluid, or intermixed gas and fluid. 
     
    
     DESCRIPTION  
       [0026]     There will now be shown and described, according to  FIG. 1 , a system for solvent evaporation that contains an automated control system for determining that solvent exchange is complete in a multi-solvent mixture. Evaporation system  100  includes a vessel  102  that contains a solvent, which contains other material, such as analytes, extractants, or reaction products (not shown). Sensors  104 ,  106  include level sensors disbursed on vessel  102  to measure the fluid properties of those contents. Sensor  108  monitors the temperature of vessel  102 . Sensor  110  is optionally used to monitor temperature of the multi-solvent mixture internally. Sensor  112  monitors internal pressure of vessel  102 . A heater  114  provides energy transfer to the multi-solvent mixture within vessel  102 . A power supply  116  drives the heater  114  and powers the system  100 . Sense circuitry  118  receives and interprets signals as values from sensors  104 ,  106 ,  108 ,  110 ,  112 , transmitting the data to controller  120 . The controller  120  monitors temperature, energy, fluid level, and/or pressure signals. The power supply  116  drives a pulse width modulation device  122  that controls the amount of power applied to heater  114  by modulation of the pulse width of the applied power. In one embodiment, the applied power may be DC current that is applied in a step-pulse with increments of applied power being separated by a periodic time interval. Controller  120  is calibrated by program instructions to deliver power according to a temperature setpoint that is associated with a periodic separation of these power pulses. Feedback signals on line  124  pertain to power consumption through the PWM device  122 . These signals may represent, for example, voltage, amperage, and/or power, which controller  120  uses to adjust the power consumption. Tubing  126  receives solvent vapors for vapor and liquid discharge through a vacuum pump (not shown) that may be used to facilitate solvent evaporation by lowering pressure within vessel  102  to a predetermined level that is programmed into controller  120 . A sample transfer tubing  128  may be used to collect samples of fluid from within vessel  102 . Injection tubing  130  may be used to inject or introduce fluids into the vessel  102 . The controller  120  is conFig.d with program instructions and circuitry to automate the removal of solvent from vessel  102  according to the instrumentalities discussed below.  
         [0027]      FIG. 2  provides additional detail with respect to the vessel  102 . A manifold  200  and O-ring  202  seal the top  204  of vessel  102  to provide a lid that communicates tubing  126 , sample transfer tubing  128 , and injection tubing  130  to the interior of vessel  102 . By way of example, a fluid stream may be introduced through tubing  130  from an inline process or container (not shown). Once all the fluid is collected, the sample is transferred through tubing  128  to a storage vessel  206 . Sensors  104  and  106  can be adjusted to a desired level using adjustment rod  208  to define regions that pertain to sensors  104  and  106  according to labeled Zone  1 , Zone,  2 , and Zone  3 . Each Zone creates a region that is controlled through controller  120  for pressure and rate of energy that applied through the PWM  122 . Sensor  106  may be selectively controlled through the controller  120  to define and/or determine the final level endpoint after the fluid is collected.  
         [0028]      FIG. 3  is a midsectional view of vessel  102  showing an optimized placement as an off-center location for a negative pressure port  300  that turbulates the evaporating fluid and rinse solutions within vessel  102 . The negative pressure port  300  is placed to flow in a direction that is off center or transversely of the axis of symmetry of vessel  102 . The fluid stream injection tubing  128  is placed to inject in the center or generally parallel to the axis of symmetry. Negative pressure is applied to port  300  while positive fluid or air pressure is introduced through tubing  128 . The placement of tubing  128  and port  300  in these orientations and at these conditions causes a flow imbalance within vessel  102  that imparts a fluidic mixing action without the aid of a mechanical stirring mechanism. The flow imbalance through tubing  128  and port  300  may be adjusted by changing a flow restriction (not shown) on either or both tubing  128  and  300 . Flow entering the tubing  128  creates a downward force in the general center of vessel  102 , while flow being pulled through port  300  pulls upward at the circumference of vessel  102 . This opposition of forces is useful in rinsing vessel  102  between introduction periods of the collected fluid stream to keep sample materials dissolved in the fluid  302  inside vessel  102 . During the final rinsing period of vessel  102  to remove the contents thereof, the imbalance between tubing  128  and port  300  is increased to a level that causes turbulence inside vessel  102  and facilitates the cleaning of vessel  102 .  
         [0029]      FIG. 4  shows a flow balancing tee  400  that may be used in top  204  to isolate the fluid delivery of an inline process from the evaporation process of the system  100 . An entrance port  402 , exit  404 , and evaporation process port  406  are connected by conduit  408 . The evaporation process port  406  is used to move fluid to the evaporation process within vessel  102 .  
         [0030]      FIG. 5  shows control circuitry  500  that may be used to detect a failure or open circuit in the heater  114 . The heater  114  is powered by applying voltage to a resistive heater element  502  and dual inline diodes  504  and  506  according to optimization principles that are discussed below. The modulating circuitry unit  508  controls switch  510  at a p-reset or variable rate according to instructions from controller  120 . During the time period that switch  510  is closed to energized heater element  502 , voltage is applied to heater element  502 , and diodes  504 ,  506 . The voltage applied to diodes  504  and  506  during this time creates a voltage bias each time the voltage is applied at the top of both diodes to energize an opto-isolater  510  and activate an input to a micro controller (MCU), The MCU can determine if the heater element  108  or circuit controlling  108  is open. Opto-isolater  510  isolates the MCU and the heater element  502 , giving protection to the MCU.  
         [0031]      FIG. 6  shows the balancing tee  400  that is used in the evaporation system to isolate the fluid delivery of the inline process from the evaporation process. Operation of valves V 1  and V 2  is governed by controller  120 . Fluid from an inline flow process enters port  402  through V 1  and exits through port  404 . Port  404  is vented to atmosphere through condenser tubing  601 , which also serves a reservoir for the inline flow process. Port  406  is governed through use of valve V 2 . Negative pressure is applied to vessel  102  through port  300  with commensurate mixing action being achieved through tubing  128  as previously described. Port  406  is unblocked at controllable intervals through the controller  120  by opening V 2 . The balancing tee  400  allows the fluid in line  601  to be moved into vessel  102  when port  406  is unblocked through V 2 . Make up airflow is provided through line  601 , which is vented to atmosphere. The inline fluid stream in not affected due to the venting of polts  404 ,  406  during the period that V 2  is open. Thus, the inline flow process is not affected by the pressure change when V 2  is unblocked.  
         [0032]      FIG. 8  shows a systematic comparison of temperature values between a set point that is a predetermined temperature value programmable set by controller  120  as an intended value, versus an actual temperature that is measured form the vessel  102 . The comparison shows that the intended temperature of the set point is achieved by adjustment of the power that is delivered to the heater  114 . The system  100  programmatically determines temperature setpoint targets for each of the stair-stepped intervals from approximately 1 second to 501 seconds, 1101 seconds to 1401 seconds, and 2001 seconds to 2701 seconds, as these represent inherent boiling points of the respective solvents at these times. These boiling points are used to fractionate multiple solvents from a solvent mixture in vessel  102 . Accordingly, interval A pertains to partial removal of a dichloromethane (DCM) solvent at a first temperature according to the boiling point of DCM. Hexane is added at interval A′, which raises the boiling point for interval B while the remaining DCM is fractionated from the resultant mixture. No additional solvent is added in interval B′, and hexane solvent is removed at the boiling point of interval C. Thus process completes a solvent exchange from DCM to hexane, with rinsing of vessel  102  by the hexane solvent, followed by partial removal of the hexane solvent to concentrate the materials that are dissolved in the solvent.  
         [0033]      FIG. 8A  shows an intelligent algorithm through which the controller  120  determines a boiling point of a solution in vessel  102 . In this case, a DCM solvent is subjected to heating through use of a PWM-based scaled average power system input under automated control of controller  120 . The PWM technique is set at a constant interval intended to produce a temperature  800 , which is above the boiling point of DCM. The temperature  802  represents the boiling point of DCM and so is relatively constant (where the DCM is at constant pressure). The sensed temperature  804  jumps at  804  to indicate that the DCM solvent is evaporated, and this jump is interpreted as such by controller  120  to commence the addition of hexane solvent.  
         [0034]      FIG. 8B  shows the temperature of ethyl acetate solvent in context of a PWM-based scaled average power system input under automated control. This intelligent algorithm includes a set point  804  that matches the boiling point of the solvent, which is at a sensed temperature  806 . The controller  120  observes a temperature plateau over interval  808  and matches this to a lookup table of possible setpoints  804  to determine the type of solvent that is being used. Alternatively, the setpoint is set by an operator, perhaps by identifying the type of solvent. The plateau is determined where additional power applied as thermal input to the vessel  102  does not raise the boiling point at constant system pressure. Interval  810  shows that the temperature has risen to the intended setpoint after removal of the solvent.  
         [0035]      FIG. 8C  shows a Fig. like that of  FIG. 8B , but for cyclohexane at a setpoint of 75° C. and 250 Torr.  
         [0036]      FIG. 8D  shows a Fig. like that of  FIG. 8B , but for ethyl acetate/Cyclohexane 1:1 solvent at a setpoint of 70° C. and 250 Torr.  
         [0037]      FIG. 9  applies the foregoing principles to illustrate a control algorithm for power limiting to prevent thermal cycling or bumping of the system  100  under automated control. It will be appreciated that the applied power in region  900  is spikey, but generally averages out along the setpoint  804  or boiling point  806 . However, at transition  902 , this spikiness narrows and trends upward just before the transition at point  803 . At this point, system power may be reduced to level  904  though the PWM technique to prevent thermal cycling, since it is no longer necessary to have large excess power for the phase change of he solvent. This is possible or even necessary because the solvent is largely evaporated. If the power is not reduced at this time, there may be miniature eruptions of the solidifying matter within vessel  102 , and the interior of vessel  102  becomes increasingly difficulty to clean with each such eruption.  
         [0038]      FIG. 10  shows detection of complete fluid dryness under automated control. Dryness is indicated by a steep drop  1000  in the required power input to maintain a given temperature, as is also evident from a derivative  1002  of average power input taken with respect to time. The derivative  1002  may be approximated by a numerical methods technique, such as by averaging power over a time interval and taking a first forward difference of the average values.  
         [0039]      FIG. 11  shows analog to digital signal conversion values for boiling detection or presence of fluid.  FIG. 11  presents values that are algorithmically derived from the direct monitoring an analog to digital converter of controller  120  as signal inputs from the level sensors  104  or  106  (see also  FIG. 2 ). An algorithm is derived from the inputs  104  or  106  to provide a change in sensor count, as shown in  FIG. 11 . The algorithm is determined directly from the number of counts in a monitored time period, e.g., as a period of 100 seconds indicated on the horizontal axis of  FIG. 11 . At each interval, the count for that interval is compared to the total count for the total elapsed time and converted to a percentage. The detection of boiling or nature of the boiling is derived from the algorithm. A zero count into the algorithm out puts no liquid present. A 100 percent count outputs total blockage or fluid present. A percentage between 0-99 is a relative indicator of the vigor of action in the fluid that is being boiled. The controller  120  may be preprogrammed to limit the vigor of action using this relative indicator.  
         [0040]      FIG. 12  shows a transport tube  1301  passing through flow sensor  1302 . Gas, liquid or intermixed gas and fluid can move through tube  1301 . Sensor  1302  is made up of a light source and light source receiver on opposing sides of the transport tube  1301 . As material moves through tube  1301  it interrupts the light path and so is detected by the receiver in sensor  302 . Algorithmically, the controller  120  monitors the output of the receiver in  1302  and detects the frequency change of the output signal from the detector. This value is compared to a trigger level to determine the presence or non presence of gas, fluid or intermixed gas and fluid in the moving fluid stream. A transport tube  1301  of this nature may be placed in any tube of system  100  to facilitate control instructions that benefit form knowledge that gas and liquid are jointly moving through the tube.