Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 210

2.62.4 Flow injection analysis
Nakashima et al. [439] determined nitrate in non saline waters by the flow-injection
analysis technique, according to which the sample 650µL)was injected into the carrier
solutions (a mixture of EDTA and ammonium chloride in aqueous solution at pH 8.1)
and the nitrate first reduced to nitrite by passage through a column of copperised
cadmium. The nitrite was then reacted with a mixture of p -aminoacetophenone and n -
phenylene-diamine and the absorption measured as 456nm. The influence of several
variables on the accuracy and sensitivity of the method was investigated. The limit of
detection was 1.5µg L −1 and the sample rate about 40 samples per hour. Relative standard
deviations for nitrate nitrogen in the range 0.1-0.3mg L −1 were about 1%.
Al-Wehaid and Townshead [440] give details of a procedure for the determination of
traces of nitrate (0.02-5mg L −1 nitrogen) in water by flow injection analysis. Trivalent
titanium chloride was used to reduce nitrate to nitrite before diazotisation with
sulphanilamide and N- (1-naphthyl) ethylenediamine, and spectrophotometric
determination at 530nm. Divalent copper was the only common ion that caused
interference and this could be removed by an on-line cation exchange mini column.
Discrete injection segmented flow analysis has been used [441] to determine nitrate
and phosphate in small volume samples.
An automatic flow-injection analyser for spectrophotometric monitoring of nitrite in
the field by reduction with copperised cadmium and derivatisation by N- 1-
naphthylethylenediamine dihydrochloride and sulphanilamide has been described [442].
The linear calibration range on the method was 0-12mg nitrate nitrogen per litre.
Various other workers [443-445] have studied the application of this technique in the
determination of nitrates.

2.62.5 Electrochemical methods
Electrochemical methods that have been used to determine nitrate include polarogrpahy
[446,447] and voltammetric analysis 448]. Bodini and Sawyer [449] described a
voltammetric determination of nitrate at the µg L −1 level. This electrocatalytic method
utilises the concomitant reduction of cupric chloride and cadmic chloride on pyrolytic
graphite to catalyse the reduction of nitrate ion.

Table 2.8 Instrumental components

Components Model or size Manufacturer

Microwave generator MR-3S Ito Chotanpa Co Ltd

TM 010 type Microwave cavity laboratory constructed

discharge tube 6mm od

3mm id

laboratory constructed

Monochromator JE-50E Nippon Jarrell-Ash Co Ltd