Abstract:
A purge and trap sample concentrator system is disclosed. The system includes a non-contact foam sensor positioned proximate an outside surface of a sparge vessel. The sensor is configured to detect foam within the sparge vessel. The system also includes a container for holding a defoaming agent, and a fluid communication line connecting the container to the sparge vessel. The system also includes a pump for selectively pumping a quantity of the defoaming agent through the fluid communication path. Finally, the system includes a processor for receiving a signal from the non-contact foam sensor. The signal is indicative of foam within the sparge vessel. The processor is configured to turn the pump on and off based at least in part on the signal.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to purge and trap equipment that supplies samples for analysis. In particular, the present invention relates to foam detection and prevention within purge and trap systems.  
         BACKGROUND OF THE INVENTION  
         [0002]    Purge and trap equipment has been widely used to extract volatile organic compounds (VOC&#39;s) from a solid or a liquid sample matrix for introduction into an analysis system for separation and identification. In many cases, the VOC&#39;s are concentrated onto an absorbent trap, followed by thermal desorption into a gas chromatograph. Sample matrices can range from soil, plastics, food, flavor, fragrance, emulsions, and water. Purge and trap sample concentration has evolved as a standardized protocol for analyzing environmental samples (i.e., soil, water, etc.). Additionally, several regulatory agencies including the United States Environmental Protection Agency (USEPA), the United States Department of Energy (USDOE), and the United States Department of Defense (USDOD) have instituted methodologies based upon purge and trap sample concentration.  
           [0003]    During operation of a typical purge and trap concentrator, purge gas (commonly helium or nitrogen of high purity) is passed through the bottom of a fritted sparge vessel (also known as a purge chamber or a purge device) before it makes contact with a sample. The frit disburses the gas into finely divided bubbles thereby allowing a large surface area of the sample to be contacted. This process allows the inert gas stream to strip the analytes from the sample matrix and concentrate them on an absorbent trap. The VOC&#39;s are then released through a sample pathway to a detection system.  
           [0004]    In the event of a foaming sample, the sample pathway may become contaminated or possibly destroyed. This causes system down time, expensive repair costs and/or loss of the particular sample associated with the foam. Given these and other difficulties associated with foam, foaming samples present special challenges for purge and trap concentrator systems.  
         SUMMARY OF THE INVENTION  
         [0005]    One aspect of the present invention pertains to a purge and trap sample concentrator system. The system includes a non-contact foam sensor positioned proximate an outside surface of a sparge vessel. The sensor is configured to detect foam within the sparge vessel. The system also includes a container for holding a defoaming agent, and a fluid communication line connecting the container to the sparge vessel. The system also includes a pump for selectively pumping a quantity of the defoaming agent through the fluid communication path. Finally, the system includes a processor for receiving a signal from the non-contact foam sensor. The signal is indicative of foam within the sparge vessel. The processor is configured to turn the pump on and off based at least in part on the signal.  
           [0006]    Another aspect of the present invention pertains to a sensor for detecting foam in a purge and trap sample concentrator. The sensor includes an optical detecting element configured to mount proximate an outside surface of a sparge vessel. The optical detecting element is further configured to detect foam within the sparge vessel.  
           [0007]    Yet another aspect of the present invention pertains to a method of operating a purge and trap sample concentrator. The method comprises utilizing a non-contact sensor to detect foam within a sparge vessel. The method also includes generating a signal based on foam detection, and pumping a defoaming agent out of a container and into the sparge vessel based on the signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a diagramatic view of an automatic analysis system.  
         [0009]    [0009]FIG. 2 is a schematic illustration of a purge and trap system.  
         [0010]    [0010]FIG. 3 is schematic illustration of a pump and valve combination associated with the purge and trap system in a first operational state.  
         [0011]    [0011]FIG. 4 is schematic illustration of a pump and valve combination associated with the purge and trap system in a second operational state.  
         [0012]    [0012]FIG. 5 is schematic illustration of a pump and valve combination associated with the purge and trap system in a third operational state. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    [0013]FIG. 1 is a diagramatic view of an automatic analysis system in which embodiments of the present invention are particularly useful. System  100  includes multiple vial autosampler  102 , purge and trap sample concentrator  104 , and gas chromatograph  106 . Autosampler  102  is adapted to receive and maintain a number of vials containing samples. Auto sampler  102  is generally equipped with a robotic system to pick a given vial from its respective position and move it to an analyzation site where a sample is removed from the vial. Generally, the sample is tested for volatile organic components. Examples of auto sampler  102  can be purchased from Tekmar Company of Mason, Ohio under the trade designation SOLATEK 72.  
         [0014]    A sample derived from auto sampler  102  is illustratively conveyed to purge and trap concentrator  104 . Concentrator  104  then extracts volatile organic compounds from the sample matrix such that they can be provided to gas chromatograph  106 . As indicated in FIG. 1, concentrator  104  includes a sparge vessel  108  through which a purge gas is bubbled in order to extract VOC&#39;s from the sample matrix. Purge and trap sample concentrators can be obtained from Tekmar Company under the trade designations Model LSC-1, LSC-2, LSC-3, and 3100.  
         [0015]    [0015]FIG. 2 is a schematic illustration of a purge and trap system  200  in accordance with one aspect of the present invention. System  200  is one example of a system that could be implemented in the context of purge and trap sample concentrator  104  in FIG. 1. Operation of system  200  will be described below in detail.  
         [0016]    A significant function associated with system  200  is an ability to detect and compromise a foaming aqueous sample. This function is accomplished through operation of a non-contact sensor that is utilized to detect foam arising from a solution under analysis, and is further accomplished through operation of a pump and valve system that supplies a defoaming agent to destroy or otherwise compromise undesirable foam. After the foam has been destroyed, the non-contact sensor detects the elimination of foam and sends a corresponding signal. In response to the signal, gas is channeled through key system components for the purpose of removing fluids associated with leftover defoaming agents.  
         [0017]    Operation of purge and trap system  200  will now be described in greater detail. System  200  includes a processor  204  that is configured to control other components of system  200 . Processor  204  is illustratively a computer processing unit. Processor  204  is functionally connected to a pump  206 , a first valve  208 , a second valve  210 , and a sensor  212 . Processor  204  receives signals from sensor  212  and, at least partially based on the received signals, controls pump  206 , valve  208  and valve  210 .  
         [0018]    During standard operation of purge and trap system  200 , an aqueous sample is placed within a sparge vessel  214  and purged with gas (i.e., helium) to entrain VOC&#39;s. The gas is illustratively transferred from a sample manifold  216  through a T-connector  218  into sparge vessel  214  at connection  220 . As the sample is purged with gas, VOC&#39;s are released through a sample pathway  222  to a detection system  224 .  
         [0019]    As gas is transferred for purging from sample manifold  216  through T-connector  218 , gas is also channeled through T-connector  218  up to a valve  208 . Valve  208  has three valve components, namely, valve component  230 , valve component  232 , and valve component  234 . While the sample is being purged within sparge vessel  214 , valve component  232  remains closed such that gas is prevented from entering valve  208 . Valve component  234  remains open and valve component  230 , which is a common valve, always remains open.  
         [0020]    Valve  210  includes valve components  236 ,  238 , and  240 . Valve component  236  is a common valve and is therefore always open. While the sample is being purged within sparge vessel  214 , valve component  238  illustratively remains open, and valve component  240  illustratively remains closed.  
         [0021]    Processor  204  is configured to selectively open and shut valve components  234  and  232 , as well as valve components  238  and  240 . Processor  204  is also configured to turn pump  206  on and off, wherein when pump  206  is on it pumps a defoaming agent  240  from a container and into valve  208  (when component  234  is open).  
         [0022]    As was described above, when a sample is being purged within sparge vessel  214 , foam that rises from the sample can cause various system failures. In accordance with one aspect of the present invention, sensor system  212  is positioned proximate sparge vessel  214 . In accordance with one embodiment, sensor system  212  is positioned proximate a glassware bulb portion of sparge vessel  214 .  
         [0023]    In accordance with one aspect of the present invention, sensor system  212  is a non-contact sensor designed to detect foam within sparge vessel  214  without making direct contact with the foam (e.g., only a transmitted signal contacts foam). Sensor system  212  illustratively includes an emitter  211  positioned on a first side of a glass portion of vessel  214 , and a detector  213  positioned on an opposite side. In accordance with one embodiment, emitter  211  is a light emitter and detector  213  is a corresponding light detector. In accordance with another embodiment, emitter  211  is a sound wave emitter and detector  213  is a sound wave detector. Regardless of the precise nature of the signal being utilized, emitter  211  illustratively transmits a signal through sparge vessel  214  to detector  213 . In accordance with one embodiment, an emitter is utilized without a detector (e.g., the emitter monitors its own signal). In accordance with another embodiment, a detector is utilized without an emitter (e.g., presence or absence of ambient light passing through vessel is monitored).  
         [0024]    When a sample being purged in vessel  214  begins to foam, the foam will rise up and interrupt the signal being transmitted between emitter  211  and detector  213 . For example, rising foam will disperse light being transmitted from emitter  211  and prevent it from reaching detector  213 . In instances where there is no detector, the emitter illustratively monitors interruption of its own signal. In accordance with another embodiment, sensor system  212  is an audio-oriented sensor that monitors for the “sound” of foam within sparge vessel  214 . Regardless of the precise nature of non-contact sensor system  212 , the associated sensing of foam is illustratively managed and monitored by processor  204 . Simply for the sake of simplifying description of an embodiment of the present invention, a sensor system  212  is illustrated comprising an optical system having an optical signal transmitted between an emitter and detector will be assumed.  
         [0025]    When the signal between emitter  211  and detector  213  is interrupted, processor  204  illustratively executes a series of commands. First, the gas supply from sample manifold  216  is optionally shut off such that gas is no longer supplied through connection  220  to the sample located in sparge vessel  214 . Next, valve  210  is toggled such that valve component  238  becomes closed, and valve  240  becomes opened. Then, defoaming agent  240  is pumped by pump  206  through valve component  234 , into valve  208 , through valve component  230 , through valve component  236 , into valve  210 , through valve component  240 , and then through an extension  244  in the upper portion of sparge vessel  214 . In this way, defoaming agent is utilized to eliminate foam that has built up in the upper portions of sparge vessel  214 .  
         [0026]    When the foam has been eliminated, the signal between emitter  211  and detector  213  will be restored. In response to the restoration of the signal, processor  204  turns off-pump  206  and toggles valve  208  such that valve component  234  becomes closed and valve component  232  becomes open. At the same time, valve  210  is toggled such that valve component  240  again becomes closed and valve component  238  again becomes opened.  
         [0027]    The gas supply from sample manifold  216  is then turned on such that gas is again supplied to T-connection  218 . Given the updated status of valves  208  and  210 , gas will now move through valve component  232  and into valve  208 . The gas is then channeled through valve component  230 , through valve component  236  and into valve  210 . The gas then moves through valve component  238  and into the container holding defoaming agent  240 . In this manner, valves  208  and  210 , as well as associated pumping lines, are swept clean (i.e., swept free of defoaming agent  240 ).  
         [0028]    Next, at the conclusion of a preset time, processor  204  toggles valve  208  to its original configuration wherein valve component  234  is open and valve component  232  is closed. Gas is again channeled from sample manifold  216  through connection  220  and into sparge vessel  214  for normal operation of system  200 . In this way, system  200  enables the protection of sample pathways while still enabling the analysis of VOC&#39;s in foaming aqueous samples.  
         [0029]    As was described above, during the processes of operation associated with purge and trap system  200 , valves  208  and  210  work in association with one another to achieve various operational states. FIG. 3 is a schematic illustration of valve  208 , valve  210  and pump  206  in a first operational state, wherein, with reference to FIG. 2, gas is flowing from sample manifold  216 , through connection  220 , and to sparge vessel  214 . In this first operational state, pump  206  is off and therefore does not pump defoaming agent  240  into valve  208  or valve  210 . As is illustrated, valve component  232  is closed and therefore prevents gas from flowing from sample manifold  216  through T-connection  218  and into valve  208 .  
         [0030]    [0030]FIG. 4 is a schematic illustration of valve  208 , valve  210  and pump  206  in a second operational state that is achieved after foam has been detected by sensor system  212 . In the second operational state, valve  210  has been toggled such that valve component  238  has been closed and valve  240  has been opened. During this second operational state, pump  206  is turned on such that defoaming agent  240  is pumped through valve component  234 , into valve  208 , through valve component  230 , through valve component  236 , into valve  210 , through valve component  240 , through connection point  244  and into sparge vessel  214 .  
         [0031]    [0031]FIG. 5 is a schematic illustration of valve  208 , valve  210  and pump  206  in a third operational state, wherein sensor system  212  has now detected that there is no longer foam in sparge vessel  214 . In this third operational state, pump  206  is turned off such that defoaming agent  240  is no longer being pumped into valve  208 . In addition, valve component  234  of valve  208  is closed to prevent entry of defoaming agent  240 . Gas is channeled from sample manifold  216  through valve component  232 , into valve  208 , through valve component  230 , through valve component  236 , into valve  210 , through valve component  238  and into the container holding defoaming agent  240 . In this way, valve  208  and valve  210 , as well as associated pumping lines, are swept with gas. After the sweeping process has occurred, processor  204  toggles valve  208  in order to bring system  200  back to the first operational state, as is illustrated in FIG. 3. In this configuration, system  200  accommodates the standard purge and trap sample concentration functionality.  
         [0032]    Processor  204  illustratively causes the rotation between operational states to be repeated when sensor system  212  detects foam within sparge vessel  214 . Processor  204  receives the detection signals from sensor system  212  and controls pump  206 , valve  208  and valve  210  in order to transfer system  200  between the various operational states. The described process protects sample pathways and still allows for the analysis of VOC&#39;s in foaming aqueous samples.  
         [0033]    Although the present invention has been described with reference to illustrative embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.