Analytical method and apparatus

Abstract

Method and apparatus for detecting and/or determining ethanol in fluid samples using a substantially non-porous barrier of un-plasticized polyvinyl chloride (PVC) interposed between the sample to be analyzed and a detecting means responsive to ethanol. The ethanol diffuses through the barrier membrane and then is measured at the detecting means. The PVC membrane can be made by solvent casting, and is usually 10 to 40 um thick. Measurement can be by any known means, but preferably electrochemically (amperometrically). The PVC membrane may be part of a multiple membrane system. The method and sensor are useful for analyzing alcoholic liquors or beverages (for example beer, wine and other fermentation products), in their final form or at intermediate stages of their manufacture or storage, and also for the monitoring of a wide range of process, waste and effluent liquids.

1 . A method for detecting and/or determining ethanol in fluid samples which comprises interposing a membrane barrier composed of polyvinyl chloride (PVC) in un-plasticised form between the sample to be analysed and a detecting means providing an output representative of the content of said ethanol and allowing the ethanol to diffuse through the said barrier membrane and then measuring its presence at the detecting means.  
     
     
         2 . A method for detecting and/or determining ethanol in fluid samples by allowing the ethanol to diffuse from a sample under examination through a barrier membrane to an ethanol-responsive detector means, characterised in that the barrier membrane is composed of polyvinyl chloride (PVC) in un-plasticised form.  
     
     
         3 . A method as claimed in  claim 1  or  claim 2  wherein the PVC is substantially non-porous.  
     
     
         4 . A method as claimed in any of  claims 1  to  3  wherein the molecular weight of the PVC is in the range 10,000 to 200,000.  
     
     
         5 . A method as claimed in any of  claims 1  to  4  wherein the un-plasticised polyvinyl chloride may be made into membranes by solution casting techniques, using solvents to dissolve the polymer and then forming the PVC film from the solution of PVC.  
     
     
         6 . A method as claimed in any of  claims 1  to  5  wherein the thickness of the membrane is in the range 10 to 40 μm,  
     
     
         7 . A method as claimed in any of  claims 1  to  6  wherein the detecting means is one of an electrochemical nature, e.g. potentiometric or, preferably, amperometric.  
     
     
         8 . A method as claimed in any of  claims 1  to  7  wherein the detecting comprises an electrode system and a liquid or gel phase electrolyte-containing medium, preferably aqueous or aqueous-based.  
     
     
         9 . A method as claimed in any of  claims 1  to  8  wherein the temperature of use of the sensor is around ambient temperatures, e.g. in the range 5 to 40 degrees C.  
     
     
         10 . A method as claimed in any of  claims 1  to  9  wherein the un-plasticised PVC membrane is used in conjunction with one or more other membranes, e.g. a dialysis membrane.  
     
     
         11 . A method for detecting or determining ethanol substantially as described.  
     
     
         12 . A sensor device for detecting ethanol present in fluid  10  samples, using a method as claimed in any of  claims 1  to  11 .  
     
     
         13 . A sensor device for detecting ethanol present in fluid samples and providing an output representative of the ethanol content of said sample comprising comprising an ethanol-detecting means and a membrane barrier between the said ethanol-detecting means and the sample to be analysed, characterised in that the membrane barrier is composed of polyvinyl chloride (PVC) itself, in un-plasticised form.  
     
     
         14 . A sensor device as claimed in  claim 12  or  claim 13  which comprises comprises a detecting means in contact with an electrolyte medium and both associated with a membrane of polyvinyl chloride (PVC) itself, in un-plasticised form, which provides an interface for contact with a sample to be analysed and interposed between the active electrode (anode) of the cell used as detector.  
     
     
         15 . A sensor device as claimed in  claim 14  wherein the active electrode is a metal electrode, especially a platinum anode, conveniently made in combination with a silver/silver chloride counter electrode, as for example in the so-called Clark electrode, which comprises a platinum electrode surrounded, wholly or partially, by a silver/silver chloride ring.  
     
     
         16 . A sensor device as claimed in any of  claims 12  to  15  in which the un-plasticised PVC membrane is put directly on to the detector means when this is an electrode, and relying on the external wetting of this combination with the sample to produce the electrolyte contact with the electrode as required to make the electrochemical operation of the detector means function.  
     
     
         17 . A sensor device for detecting and/or determining ethanol in fluid samples substantially as described.  
     
     
         18 . Use of a method or sensor as claimed in any  claims 1  to  17  for the analysis of alcoholic liquors or beverages (for example beer, wines and other fermentation products), in their final form or at intermediate stages in their manufacture or storage.