Interferences with nitrite determination, sulphide

Sulphide ions have been reported to interfere with the determination of nitrite. Thus, when hydrogen sulphide is suspected to be present in a sample, the gas should be expelled with nitrogen after the addition of the acid sulphanilamide reagent... 

The automation or semi-automation of a conventional manual method by FIA often results in a decrease in the number and level of interferents. Thus, in the FIA version of the determination of cyanide by the classical reaction with barbituric acid/chloramine T, nitrite and sulphide pose no Interference at concentrations ten times as high as that of the analyte, which is otherwise adversely affected by the presence of both interferents in the manual method [48], The greater tolerance to foreign species in FIA methods can be generally attributed to their kinetic character, so that undesirable side reactions scarcely have the opportunity to develop to an appreciable extent in such a short interval as the residence time. The tolerance to extransous species is even more remarkable in kinetic FIA methods based on the measurement of a reaction rate (stopped-flow). Optimization of FIA systems as regards selectivity is a relatively simple task on account of their enormous versatility. 

Funazo et al. [812] have described a method for the determination of cyanide in water in which the cyanide ion is converted into benzonitrile by reaction with aniline, sodium nitrite and cupric sulphate. The benzonitrile is extracted into chloroform and determined by gas chromatography with a flame ionisation detector. The detection limit for potassium cyanide is 3 mg L 1. Lead, zinc and sulphide ion interfere at lOOmg L 1 but not at lOmgL-1. 

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See also in sourсe #XX -- [ ]

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