Chemical sensing apparatus

Abstract

In an improved amperometric gas sensor, the structure, composition, and electrode potential are adjusted so as to prevent or minimize any unwanted reactivity at the counter and/or reference electrode of any analyte or interfering component of the matrix that may cross over thereto. The sensor is preferably structured so that the product of the analyte reaction at a first working electrode can be reconverted to the original analyte at a counter electrode or at a second working electrode and then reacted again at the first working electrode, with such back-and-forth reactions repeating many times, so as to yield an amplification of the analyte signal.

1 . Amperometric sensing apparatus for detecting an analyte in a gaseous medium, which comprises: 
 a working electrode at which said analyte is caused to participate in an analyte half-cell reaction:    a reference electrode for controlling the electrochemical potential of said working electrode;    a counter electrode at which a complementary half-cell reaction is caused to occur; wherein all three electrodes are electrochemically connected through an electrolyte; and    means for preventing or minimizing the occurrence of said analyte reaction or reaction of any interfering gas at said counter electrode and/or reference electrode,    wherein said counter and/or reference electrode comprises a material selected to minimize said analyte reaction.    
   
   
       2 . The apparatus of  claim 1 , wherein said material is a catalyst which is poisoned towards the analyte reaction.  
   
   
       3 . The apparatus of  claim 1 , wherein the potential of the counter electrode is maintained at a value which renders it inactive to the analyte reaction.  
   
   
       4 . Amperometric sensing apparatus for detecting an analyte in a gaseous medium, which comprises: 
 a working electrode at which said analyte is caused to participate in an analyte half-cell reaction:    a reference electrode for controlling the electrochemical potential of said working electrode;    a counter electrode at which a complementary half-cell reaction is caused to occur; wherein all three electrodes are electrochemically connected through an electrolyte; and    means for preventing or minimizing the occurrence of said analyte reaction or reaction of any interfering gas at said counter electrode and/or reference electrode,    wherein said means comprises a barrier which prevents or minimizes access of said analyte to said counter and/or reference electrode.    
   
   
       5 . The apparatus of  claim 4 , wherein said barrier comprises a scavenger material or electrode at which the analyte reacts before it can reach the counter and/or reference electrode.  
   
   
       6 . The apparatus of  claim 4 , wherein said barrier comprises a lengthy path through the electrolyte between the working and counter and/or reference electrodes.  
   
   
       7 . The apparatus of  claim 1 , wherein said material comprises a gaseous or liquid reagent which results in the predominance of a complementary reaction at the counter electrode to the exclusion of the analyte reaction.  
   
   
       8 . The apparatus of  claim 1 , wherein said analyte is CO or H 2  and said material comprises Ir or oxides of Ir, Au, Pb/PbO 2 , Ag/AgCl, Ru, Pd, low-surface-area Pt or any other substance at which electro-oxidation of CO and/or 12 or other interfering gas is hindered.  
   
   
       9 . The apparatus of  claim 8 , wherein said analyte is H 2  and wherein the means for preventing the occurrence of interfering gas such as CO at the counter and/or reference electrode is a barrier over the entrance to the gas sensor comprising a thin film of material that is highly permeable to H 2  but impermeable to CO and other interferences.  
   
   
       10 . The apparatus of  claim 9 , wherein said material is FEP Teflon about 0.002″ thick.  
   
   
       11 . The apparatus of  claim 4 , wherein said barrier comprises a coating of Nafion or other material over the counter electrode.  
   
   
       12 . The apparatus of  claim 7 , wherein said analyte is oxidizable and said material comprises oxygen that is fed to the counter electrode through a separate hole.  
   
   
       13 . The apparatus of  claim 7 , wherein the counter and/or reference electrode is isolated from any sampled gaseous medium.  
   
   
       14 . The apparatus of  claim 1 , wherein said counter and reference electrodes are combined into a single electrode.  
   
   
       15 . The apparatus of  claim 1  comprising means of enhancing the reactivity of the counter electrode to the product of the analyte reaction.