Electrochemical apparatus for simultaneously monitoring two gases

Circuit means for providing first and second output signals in an apparatus in order to monitor the presence of first and second constitutents of a sample of gas, which apparatus includes electrochemical means for generating a first indicating signal having a characteristic resulting from the presence of the first constitutent in the sample and a second indicating signal having a characteristic resulting from the combined presence of the first and second constitutents in the sample, said circuit means comprising:

• (a) first amplifier means for amplifying the first indicating signal to provide said first output signal;
• (b) compensating means for subtracting a fractional amount of the first indicating signal from the second indicating signal to produce a difference signal having a characteristic resulting only from the presence of the second constituent in the sample;
• and
• (c) second amplifier means for amplifying said difference signal to provide said second output signal.

A method for simultaneously monitoring the presence of first and second members of a family of oxygen-containing gases in a sample of gas, said method comprising the steps of:

• (a) electroreducing at least a portion of the first member in the sample to derive a first electrical signal while forming a first gas mixture comprising electroreduction products, unreduced first member and second member;
• (b) oxidizing the second member in said first gas mixture to convert all of the second member present in said first gas mixture to the first member to form a second gas mixture;
• (c) electroreducing at least a portion of the first member and in said second gas mixture to derive a second electrical signal;
• and
• (d) electronically processing said first and second electrical signals to generate first and second output signals respectively representative of the amount of the first and second members present in the sample.

A method for manufacturing an electrode capable of electroreducing nitrogen dioxide, said method comprising the steps of:

• (a) stretching a hydrophilic porous membrane over an electrode support structure;
• (b) applying a gold resinate over the surface of said hydrophilic porous membrane;
• (c) heat curing the resinate until a coating of gold is formed on said hydrophilic porous membrane;
• and
• (d) electroplating said hydrophilic porous membrane to form a coating of silver on the exposed surface of said coating of gold.

An electrochemical means for detecting predetermined constituents in a sample of gas, said electrochemical means including:

• (a) a cell structure enclosing a supporting electrolyte;
• (b) an indicator electrode means mounted in said cell structure for generating an electrical signal in response to the presence of a predetermined atmospheric constituent, said indicator electrode means comprising a hydrophilic porous supporting membrane having a first surface which contacts said supporting electrolyte and a second surface which contacts the sample of gas, said first surface having a first layer of gold coated thereon and a second layer of silver overlying said first layer of gold;
• and
• (c) a reference electrode means mounted in said cell structure for maintaining a reference potential relative to said indicating electrode means, said reference electrode comprising a glass element in contact with said supporting electrolyte.