Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 507

7.18.9 Miscellaneous
Nitrate has been determined by a nitrate selective electrode [57] consisting of a porous
polymer wick sealed with liquid ion exchanger tris(4, 7-dipheny]-1, 10-phenanthrolinato)
nickel(II) in 2-nitro-p-cymene). Chloride and bicarbonate interferences are overcome by
the addition of silver sulphate and 0.5M phosphate buffer, pH 2 respectively.
Maracek et al. [58] investigated the feasibility of using a hanging drop electrode for the
determination of nitrate, perchlorate and iodide in potable water. A 3-electrode system
was used with a polarographic analyser. The potential range of the method was increased
by using crystal violet dicarbollylcobaltate electrolyte in the nitrobenzene phase and
magnesium sulphate in the aqueous phase, with a lead/lead sulphate reference electrode.
A nitrogen-15 isotopic tracking method has been used [59] to identify the origin of
nitrates of some aquifers in the Paris basin.
Clifford and Weber [60] have discussed the application of anion exchange resins to the
commercial scale removal of nitrate from potable water supplies.
7.19 Nitrite
See also section 7.20.
Nitrite in the environment is derived from biological denitrification, acid rain and
industrial waste. Nitrite can induce methaemoglobinaemia and react with secondary and
tertiary amines forming carcinogenic nitrosamines. Such nitrosation reactions can take
place in vivo . Even though saliva is the primary source of human exposure to nitrite, it is
desirable to monitor the nitrite level in the environment, particularly in drinking water.
7.19.1 Spectrophotometric method
The current standard method for nitrite analysis in water is based upon
Spectrophotometric determination of an azo dye formed by coupling diazotised
sulphanilamide with N -(1-naphthyl)ethylenediamine dihydrochloride (Griess reaction). It
takes about 30min; however, a parallel determination of multiple samples is possible. The
detection limit is about 10µg L −1 as nitrite if a 1cm light path is used. The problem of this
chemical method is that it is subject to interference by some reducing compounds and
metal ions or colour.
One such method [61] claims a detection-limit of 0.001mg L −1 nitrite (as N) with a
standard deviation of 0.018mg L −1 at the 0.04mg L −1 nitrite level and 0.04mg L −1 at the
1.6 mg L −1 nitrite level.
3, 3 ′ dimethylbenzidine has been used as a chromogenic reagent for the determination
of down to 5µg L −1 nitrite N in potable water. Spectrophotometric measurements are
carried out at 437µm [62]. Iron and copper interfere in this procedure. Two modifications
have been described [63] of the Griess-Ilosvay method for determination of nitrites in
drinking water. The first is based on modification of the reaction between the diazonium
salt of aniline-4-sulphonic acid with N-phenyl-1-naphthylamine-8-sulphonic acid. The
second is based on the reaction of the diazonium salt of aniline-4-sulphonic acid with N-