Study of interferences in the spectrophotometric determination of nitrite using composite diazotisation-coupling reagents

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Abstract
A study was made of 82 possible interferences in the spectrophotometric determination of nitrite by the diazotization-coupling technique using three composite reagents [sulphanilamide and N-(1-naphthyl)ethylenediamine (NED); sulphanilic acid and NED; and 4-nitroaniline and NED]. The effects of interferences when using these three reagents differ considerably in many instances. Large amounts of inert salts, such as alkali metal and ammonium sulphates, chlorides and nitrates cause high results with sulphanilic acid-NED reagent and high or low results with sulphanilamide-NED and 4-nitroaniline-NED reagents owing to the Brönsted salt effect. Carbonate, hydrogen carbonate, phosphate, pyrophosphate, tetraborate, acetate, tartrate and oxalate salts can interfere by changing the acidity of the solution or by their buffering action. This interference is less with the 4-nitroaniline-NED method than the other two methods. Silver, mercury(I), bismuth, antimony, lead, barium, strontium and calcium can interfere by precipitating as chloride, oxychloride, oxysulphate or sulphate. Chromium(III), nickel and cobalt interfere by reason of the colour of their ions. Oxidising and reducing agents usually produce low results. Aluminium, manganese, zinc, cadmium, tin(IV) mercury(II), titanium(IV), zirconium(IV), iron(III), copper(II), molybdenum(VI), tungsten(VI), arsenic(VI), uranium(VI), thallium(I), gold(III), platinum(IV), selenium(IV), bromide, iodide, thiocyanate, cyanide, cyanate, hexacyanoferrate(III) and -(II), fluoride, perchlorate and silicate can interfere in diverse ways.

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