Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 242

sulphate, chloride or ammonium.
Workers at the Water Research Centre UK [551,552] have carried out detailed
investigations of the accuracy of determination of total oxidised nitrogen and nitrite in
river waters by the Griess-Ilosvay automated spectrophotometric procedure. Broadly,
each of the 11 participating laboratories achieved total errors of not greater than ±20% of
the determined concentration or 0.1mg L −1

of nitrogen (whichever was the larger for

different sample concentrations).
T he values of S t for the two standard solutions, the river water and the spiked river
water were compared with the appropriate target value using the F-test, and were
accepted as satisfactory provided S t was not significantly greater (p=0.05) than the
appropriate target. For both total oxidised nitrogen and nitrite all laboratories achieved a
precision that was not significantly (0.05 probability level) greater than the target value.
Nagashima et al. [553] determined nitrate and nitrite by using second derivative
spectrophotometry after conversion to nitrogen monoxide. Detection limits are
5×10 −6 mol L −1 for nitrate and 1×10 −6 mol L −1 for nitrite.
A dual wavelength spectrophotometric determination of nitrate and nitrite in non saline
water has a relative standard deviation of <2% and recoveries of >95% [554]. The
method is based on the reaction of nitrate and nitrite with 2,6-xylenol in a sulphuric acid
solution.
An automated procedure utilising a Technican Autoanalyser has been described for the
determination of nitrate and nitrite in non saline waters [555].
In another study, total nitrogen (organic and inorganic) in non saline water was
oxidised by potassium persulphate at 120-124°C and the resulting nitrate was measured
spectrophotometrically at 220 and 275nm [556]. The detection limit was 0.05mg of
nitrogen L −1 , relative standard deviations were <7%, and recoveries were in the range of
94-105%.

2.64.3 Chemiluminescence method
Cerny et al. [557] and Braman and Hendrix [558] have described chemi-luminescence
methods for the determination of nitrite plus nitrate in non saline waters.
Braman and Hendrix [558] used vanadium(III) reduction with chemi-luminescence
detection to determine nanogram amounts of nitrite plus nitrate. In this method nitrite in
water samples is reduced at room temperature to nitric oxide in acidic medium containing
vanadium(III). Nitrate is also rapidly reduced after heating to 80-90°C. Nitric oxide is
removed from the reaction solution by scrubbing with helium carrier gas and is detected
by means of a chemiluminescence NO x analyser. The method has the advantage of not
requiring highly acidic solutions for nitrate reduction and has been applied to the analysis
of a variety of environmental waters.

2.64.4 Continuous flow analysis
A standard Department of the Environment UK method [559] for the determination of
total oxidised nitrogen employs continuous flow colorimetry employing sulphanilamide
chromogenic reagent with the addition of a copper/hydrazine reducing reagent for the