Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 508

ethyl-1-naphthylamine. The first produces a red violet coloration measured
photometrically at 554nm and the second a red coloration measured at 537nm.
Absorbance increased linearly over the range 1-3µg L −1 of sample. Both methods were

equally suitable for the determination of nitrites.

7.19.2 Ion chromatography
Kim and Kim [64] determined nitrite in potable water by ion exclusion chromatography
with electrochemical detection. The application of ion chromatography is also discussed
under multianion analysis in sections 7.28.2, 12.6.1 and 12.6.3.

7.20 Nitrate and nitrite

7.20.1 Spectrophotometric method
Zhou and Xie [65] give details of a rapid spectrophotometric method for the
determination of traces of nitrite and nitrate in water. In this method, nitrate is quickly
reduced to nitrite at pH 3.0 in 5min with freshly prepared cadmium sponge, which is
produced in situ by the action of zinc powder in a dilute solution of cadmium chloride in
the presence of ammonium chloride. At pH 2.0, nitrous acid diazotises with p-amino-
acetophenone, which is then coupled with N -(1-naphthyl)-ethylene-diamine. The azo dye
formed is extracted into n -butanol at pH 2.0 in the presence of β-naphthyl sulphonic acid
and aluminium nitrate.
The absorbance is measured at 550nm. The molar absorptivity of the extract is about
4.8×10 4 mol −1 cm −1 . The ions normally present in water do not interfere when sodium
metaphosphate is added as a masking agent.
In this method 20ml or less of the sample containing 0.5-10µg nitrate-nitrogen are
transferred to a 25ml graduated flask. 1.0ml of ammonium chloride is added followed by
1.0ml of potassium chloride-hydrochloric acid buffer (50ml 0.2mol L −1 KCl plus 17ml
0.2mol L −1 HCl, diluted to 200ml and adjusted to pH 1.8) 1.0ml of 0.1% w/v of cadmium
chloride and 1.0ml 5% w/v sodium metaphosphate. The pH is adjusted to pH 3.0, the
solution diluted to the mark with water and again mixed thoroughly. After addition of
100mg of zinc powder through a small glass funnel, the contents of the flask are mixed
by inverting three times within 5min (stand for 2min for clarification). Aliquots of the
clear solution are pipetted for determination of nitrite as follows.
A portion of sample solution containing 0.1-2.0µg nitrite-nitrogen is transferred in a
60ml separatory funnel. 1.0ml of p-aminoacetophenone hydrochloride solution (0.5% w/v
in 1+99 HCl) and adjusted to pH 2.0 with either 30% w/v sodium acetate solution or
hydrochloric acid. After 15min standing at room temperature, 1.0ml of N-(1-naphthyl)-
ethylenediamine dihydrochloride solution (0.5% w/v in 1+99 HCl) is added. 1.0ml of β-
naphthyl sulphonic acid 0.5% w/v and 3g of powdered aluminium nitrate are added.
Extract the azo compound into 5.0ml of n- butanol by shaking mechanically for 3min.
After clarification, the absorbance of the n-butanol layer is measured at 550nm in a 1cm
cell against a reagent blank.