Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 225

systems have been studied, as discussed below.
(a) Diazotisation reagent: o-Nitroaniline
Coupling reagent: N (1-Naphthyl)ethylene diamine dihydrochloride
Chaube et al. [488] developed a method based on these reagents in which the coupled
red-violet dye is extracted into isoamyl alcohol prior to spectroscopic evaluation at
545nm.
The effects of foreign species are shown in Table 2.37 which gives concentrations of
foreign species that cause 2% error in the determination of 0.1mg L −1 of nitrite by the
extraction method (100ml samples). Copper(II), iron(II) and sulphur dioxide interfere but
the interference of up to 100ppm of sulphur dioxide can be eliminated by oxidising it to
sulphate with hydrogen peroxide. Bismuth and iron(III) require masking with tartrate.
(b) Diazotisation reagent: p-nitroaniline
Coupling reagent: 2-methyl-8-quinolinol
Tsao and Underwood [489] give a procedure for the determination of low
concentrations of nitrite in non saline water which involves diazotisation with p -
nitroaniline and coupling of the diazonium salt with 2-methyl-8-quinolinol, followed by
solubilisation of the azo dye in aqueous hexadecyltrimethylammonium bromide.
(c) Diazotisation reagent: p-nitroaniline
Coupling reagent, 8-quinolinol
This method [490] very similar to that of Tsao and Underwood [489] except that it
does not include the use of hexadecyltrimethylammonium bromide as a solubilisation
agent for the dye.
Norwitz and Keliher [491,492] determined nitrite in non saline water using composite
reagents containing sulphanilamide, sulphanilic acid, or 4-nitroaniline as the diazolisalite
and aromatic amino and N -(1-naphthyl) ethylenediamine as the coupling agent. As a
result of this work they recommended the following composition for the composite
coupling reagents: 0.25% sulphanilamide, 0.0060% N -(1-naphthyl)ethylenediamine and
5.42% hydrochloric acid; 0.50% sulphanilic acid, 0.0050% N -(1-naphthyl)
ethylenediamine, and 0.29% hydrochloric acid; and 0.25% 4-nitroaniline, 0.010% N -(1-
naphthyl)ethylenediamine and 15.0% sulphuric acid. The wavelengths of maximal
absorption were 542, 541 and 542nm respectively. The effects of varying the ratios of the
reagents, the overall amount of the reagents, the amount of acid, and the reaction
temperature were studied, as was the effect of methanol on the colours. The importance
of the ratios of reagents as well as the overall quantities was demonstrated.