Gas Sensing Electrode
These electrodes are used to analyze gases such as NH3,
NO2, SO2, CO2, and H2S.
A specific ion electrode is used for its responsive
gas. A nitrate ion-responsive electrode is for NO2 gas while a sulphide ion-responsive electrode is used for H2S gas.
A sensor is composed of an indicator and a reference
electrode in contact with a thin film of solution which is separated from the
bulk of the sample solution by a gas-permeable membrane or an air gap. This
intermediate solution interacts with the gaseous species and it is penetrated
through the membrane or an air gap, in such a way as to produce a change in a
measured constituent H+ of the intermediate solution. This change is
then sensed by the ion-selective electrode and is related to the partial
pressure of the gaseous species in the sample.
The microporous membrane is hydrophobic, made from
polypropylene or any other fluorocarbon which allows only the dissolved gases to
pass through. The electrode Ag/AgCl and glass pH electrode is dipped in the
inner solution.
The area of the membrane being small and the volume of liquid
being less, it reaches equilibrium with the test solution rapidly.
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