Electrochemical gas detection method

Abstract

An electrochemical cell comprising an anode, a cathode and a reference electrode operating in an aqueous electrolyte is utilized for detection of noxious gases in air. The gas is oxidized at the anode and detection thereof occurs as a result of the current generated by the reaction. A fixed potential difference is maintained between the anode and the reference electrode to avoid generation of undesired current from reactions involving an oxygen-water redox couple within the cell which would invalidate anode-cathode current for gas detection purposes. The fixed potential is chosen from within the range of about 0.9 to 1.5 volts.

What is claimed is: 
     
       1. The method of quantitatively detecting a gaseous noxious atmospheric pollutant selected from the group consisting of carbon monoxide, nitric oxide, hydrocarbons, ethanol and methanol in air in an electrochemical cell comprising an anode .Iadd.having a catalyst bonded to a polytetrafluoethylene membrane to provide a porous diffusion electrode.Iaddend., a cathode, a reference electrode through which no substantial current flows, .Iadd.each of said anode, cathode and reference electrodes having a catalyst surface the catalyst of .Iaddend.said anode .Iadd.catalyst surface .Iaddend.being selected from the group consisting of platinum, rhodium, iridium, ruthenium, palladium, osmium, tungsten oxide, tungsten carbide, molybdenum oxide, molybdenum sulfide, and alloys or mixtures thereof, and an aqueous electrolyte .Iadd.within an electrolyte container .Iaddend.in contact with .Iadd.the catalyst surface of .Iaddend.said anode, cathode, and reference electrode.Iadd.said reference electrode contacting air; said anode being positioned in said cell so that one surface of said anode contacts ambient air containing said pollutant to be detected and the opposite surface contacts said electrolyte whereby the noxious pollutant to be detected migrates from the surface contacting said ambient air to the internal catalytic surface of said anode to interface with said electrolyte for electrochemical reaction in the presence of said catalyst .Iaddend.including the steps of (1) feeding an air sample containing the noxious gas to be detected to the anode of said cell, said sample being substantially free of other noxious gases; (2) maintaining said anode .Iadd.by means of a potentiostat .Iaddend.at a fixed potential of from about 0.9 to 1.5 volts with respect to the reversible hydrogen couple in the electrolyte of said cell relative to said reference electrode to oxidize said noxious gaseous substance and simultaneously insure that current due to oxygen reduction or water oxidation within said electrochemical cell is not discernible relative to the level of current produced by said oxidation of gaseous substance; and (3) measuring the current flowing between said anode and cathode of said cell to quantitatively determine the amount of said gaseous substance to be detected in said gaseous sample.Iadd., said measured current being an indication of the concentration of the gas being detected.Iaddend.. 
     
     
       2. The method of claim 1 wherein the fixed potential of said anode is maintained at a potential of from about 1.07 to 1.13 volts. .[.3. The method according to claim 1 wherein the anode of the electrochemical cell 
     
     
        is a Teflon-bonded diffusion electrode..]. 4. The method of claim 1 wherein the electrolyte is phosphoric acid. .[.5. The method of claim 1 
     
     
        wherein the electrolyte is alkali hydroxide..]. 6. The method of claim 1 wherein the electrolyte of said electrochemical cell is maintained in a 
     
     
        matrix. 7. The method of claim 1 wherein the electrolyte of said 
     
     
        electrochemical cell is free flowing. 8. The method of claim 1 wherein the noxious gas is carbon monoxide.