Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 227

(e) Diazotisation reagent: p-aminoacetobenzophenone
Coupling reagent: resorcinol
Suggested reaction sequence:
Wu and Liu [494] have described a spectrophotometric technique based on these
reactions. The method is based on the diazotisation of p- aminoacetophenole followed by
coupling with resorcinol in a sodium carbonate/sodium acetate medium to form a bright
gold water-soluble azo dye. Mercuric chloride is added to eliminate the interference of
sulphide and a composite EDTA/sodium hexametaphosphate reagent is used to mask
foreign ions.
Wu and Liu [494] examined the effect of various amounts of foreign ions on the
determination of nitrite. Most of the cations and common anions do not interfere;
sulphide, thiosulphate, tetrationate and iodide interfere but their effect can be mitigated
by adding mercuric chloride solution as indicated in the method above.
(f) Diazotisation reagent: orthanilic acid
Coupling reagent: resorcinol
Bashir et al. [495] have described a sensitive method based on these reagents which
operates over the range 1-12µg nitrite with a relative standard deviation, depending on
concentration, in the range 0.4-3.5%. Cobalt interferes seriously in this method at the
4mg L −1 level while sulphate is without interference even when present in the sample at
concentrations between 1 and 1.5g L −1 .