Interference with ammonia determination cyanide

Sulfide, cyanide, and ammonia interfere with the determination by reacting directly with the measuring membrane of the electrode. After acidification with sulfuric acid the hydrogen cyanide and hydrogen sulfide can be carefully purged out (imder hood), eliminating their interfering effect. 

High concentrations of bromide, iodide, cyanide, or sulfide ions interfere with the determination. They can damage the electrode. Free ammonia would also damage the measuring surface of the electrode dissolving the silver chloride crystals. 

To measure hardness, the sample is treated with ascorbic acid (or hydroxylamine) to reduce Fe3+ to Fe2+ and with cyanide to mask Fe2+, Cu+, and several other minor metal ions. Titration with EDTA at pH 10 in NH3 buffer then gives the total concentrations of Ca2+ and Mg2+. Ca2+ can be determined separately if the titration is carried out at pH 13 without ammonia. At this pH, Mg(OH)2 precipitates and is inaccessible to EDTA. Interference by many metal ions can be reduced by the right choice of indicators.21... 

The most frequently used detector in FI systems with gas-diffusion separation is the spectrophotometer. Quite often the gas-diffusion process offers sufficient selectivity to allow relatively non-specific chemical reactions in the acceptor stream to detect the analyte. Thus, carbon dioxide, sulfur dioxide, hydrogen sulfide, ammonia may all be determined using suitable acid-base indicators in appropriate buffer solutions used as the acceptor streams. The concentration of the buffer solutions may be adjusted to suit a certain concentration range for the analyte. In order to further enhance the selectivity and/or sensitivity more specific reagents may be introduced in the acceptor streams. In the previously mentioned example on the determination of cyanide [20] a modified pyrazolone-isonicotinic acid reaction was used for such purposes. Interferences due to Schlieren effects seem not to have been reported in gas diffusion spectrophotometric systems. This is understandable, since the matrix composition of acceptor streams is usually quite uniform, and the refractive index is little affected after absorbing the gaseous analytes. 

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