Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 241

electrocatalytically using a molybdenum catalyst [535] and polarographically using
differential pulse polarography using the reaction between nitrite ion and diphenylamine
to produce diphenyl-nitrosamine [536]. Other techniques for determining nitrite include
paper chromatography of diazo dyes to reduce interference by metals [480], stopped flow
analysis [544] and direct injection enthalpimetry [482]. Derivatisation-electron capture
gas chromatography has been used to determine µg L −1 quantities of nitrite in water
without interference from halides, nitrate, phosphate, sulphate, bicarbonate, ammonium
and alkali metals and alkaline earth metals [543].
Mureta et al. [545] have studied the effect of freezing on the stability of nitrite in
aqueous solutions. Losses of nitrite of 38-57% occurred during 15 days of frozen storage.
A Weisz ring-oven method for determining nitrite in non saline waters in the 0.1-2mg
L −1 range gave a maximum relative error of ±4% [546]. This method was based on the
reaction of nitrite with p-aminobenzoic acid to form a diazonium ion, which was then
coupled with 8-hydroxyquinoline in an alkaline medium to give a reddish orange azo dye.
The method is claimed to be simple, economical and reasonably accurate.
Sanchez-Pedrino et al. [547] utilised the inhibitory effect of nitrite ions on the
photochemical reaction between iodine and EDTA in a method for the determination of
nitrite in non saline waters.
Strehlitz et al. [548] have described a nitrite sensor based on highly sensitive nitrite
reductase mediation-coupled amperometric detection. Down to 0.1µm nitrite can be
detected.
2.64 Nitrate and nitrite
2.64.1 Titration methods
A standard method published by the Department of the Environment, UK [549] describes
a technique for the determination of total oxidised nitrogen in non saline waters. In this
method nitrite and nitrate are reduced to ammonia under alkaline conditions using
Devadas alloy. Ammonia is then distilled out and determined by titration with 0.01N
hydrochloric acid in amounts down to 3mg L −1 N.
2.64.2 Spectrophotometric methods
Two groups of workers [550,551] have discussed methods for the determination of nitrite
and nitrate in river waters.
Okada et al. [550] describe a technique for determining nitrite in river waters where the
nitrite in the water diazotises p -aminoacetophenone, which is then coupled with m -
phenylenediamine at pH 1.5-3. The 2,4-diamino-4 ′ -acetylazobenzene formed is then
measured using a spectro-photometer at 460nm. Determination of nitrate is carried out
using the same method, after the nitrate has been reduced to nitrite in a cadmium-copper
column. By this method nitrite has been determined at levels of 1µg L −1 . The ions
normally present in river waters do not interfere in this procedure. No interference is
caused by less than 10 −2 M calcium, magnesium, sodium, potassium, bicarbonate,