3. Apparatus according to claim 1 and 2, characterized in that the inner electrolyte E is an alkaline buffer solution, in particular ene sodium carbonate-sodium bicarbonate buffer solution.
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Field of application of the invention
The invention relates to a device for the electrochemical determination of small amounts of ammonia in gases. The device can be used as a detector when exceeding specified low concentrations of ammonia. In addition to the use as an alarm device and a quantitative determination of ammonia is thus possible.
Characteristic of the known state of the art
The known electrochemical devices for the determination of ammonia in gases are more potentiometric (K. Cammann, "Working with ion-sensitive electrodes", p 165 ) and voltammetric type. (G. Chuiton, Pollut. Atmos 17 (1975) These known devices have the disadvantage of lower specificity due to their measuring method, whereby a greater design effort is required to achieve sufficient selectivity.
Object of the invention
The aim of the invention is to provide an ammonia-specific sensor which, in contrast to the above-mentioned known devices has a high specificity and sensitivity with reduced design complexity.
Explanation of the essence of the invention
The object of the invention is to achieve a high selectivity by the application of a reaction specific to ammonia during the electrode process in a specially developed for the process voltametric device with three-electrode technology for the measuring method, wherein the device in combination with a gas-permeable membrane and an auxiliary electrode trouble-free measurement of ammonia permits.
According to the invention, this object is achieved by the use of an ammonia-permeable membrane, an auxiliary electrode assembly and an ammonia-specific reaction, so that during the electrode process, the disturbances in potentiometric method (by K + , NR 3 H + etc.), in voltammetric and coulometric method by electrochemically active substances occur, can be eliminated. The device consists of a voltammetric cell in tube form, which has a referential electrode (preferably an Ag / AgCl electrode or saturated calomel electrode with diaphragm or an Ag / Ag 2 O electrode without diaphragm), a counter electrode of inert material! (preferably platinum or gold), a working electrode (stationary mercury electrode on platinum, gold, silver or glassy carbon) and an alkaline Leitelektroiyten buffered property (preferably sodium carbonate-sodium bicarbonate buffer). The working electrode is pressed on the underside of the arrangement against an ammonia-permeable PTFE membrane so that a galvanic contact with the other electrodes is ensured. When using an auxiliary electrode arrangement, this is inserted between the working electrode and the gas membrane so that the latter is not touched. The arrangement is cyclic-voltametrisch or chronoamperometrisch operated, wherein mercury is oxidized and reduced again. The action of ammonia leads to a current drop during the oxidation process.