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Gas sensor
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Inventors: Hobbs, Bryan S.; Chan, Yat S.;
Assignee: City Technology Limited (Portsmouth, GB2)
Primary Examiner: Niebling; John
Assistant Examiner: Bell; Bruce F.
Attorney, Agent or Firm: Lee, Mann, Smith, McWilliams, Sweeney & Ohlson
An electrochemical gas sensor for sensing an alkaline gas such as ammonia. The sensor comprises at least sensing and counter electrodes provided in a cell containing an aqueous electrolyte, the cell further including a diffusion barrier to restrict the access of gas to the cell, and a chemical species with which the gas reacts in use to form a product which is more electrochemically active than the gas. The chemical species is one of iodine, Nesslers reagent and a solution of manganous and silver nitrates. |
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DETAILED DESCRIPTION In accordance with the present invention, an electrochemical gas sensor for sensing an alkaline gas comprises at least sensing and counter electrodes provided in a cell containing an aqueous electrolyte, the cell further including a diffusion barrier to restrict the access of gas to the cell, and a chemical species with which the gas reacts in use to form a product which is more electrochemically active than the gas, wherein the chemical species is one of: a) iodine; b) Nesslers reagent; and c) a solution of manganous and silver nitrates.
The invention is particularly suitable for the detection of ammonia and the preferred chemical reagent is iodine.
Ammonia dissolves readily in water to produce alkali in accordance with reaction (2) above and iodine reacts in the alkaline conditions formed producing iodide and iodate ions according to the equation: 60H+3I.
sub.
2 =5I+IO.
sub.
3 +3H.
sub.
2 O (3) The iodide ion (I) readily undergoes electrochemical oxidation at the sensing electrode to provide a current which is directly related to the ammonia concentration and regenerates iodine in part for further reaction: 2I=I.
sub.
2 +2e (4) The overall sensor reaction, providing a measure of the ammonia concentration is then the combination of equations (2), (3) and (4), namely: 12NH.
sub.
3 +6H.
sub.
2 O+I.
sub.
2 =2IO.
sub.
3 +12NH.
sub.
4.
sup.
+ +10e (5) Any gas producing an alkaline reaction in water would produce a response in a sensor based on reaction (5) above.
Alkaline gases include hydrazines and organic amines.
However, for most applications ammonia is the only gas likely to be present producing an alkaline reaction.
Since the iodide/iodine reaction (4) proceeds readily on moderately active catalysts, interferences from likely co-existing gases with ammonia such as carbon monoxide, hydrogen, etc.
can be avoided.
Acidic gases such as carbon dioxide, sulphur dioxide, etc.
will not react with the iodine in solution and will not therefore produce a response from the sensor provided they do not themselves undergo direct electrochemical reaction at the electrode catalyst
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Semiconductor manufacture 
