Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 274

selenite and selenate in drainage water samples and was effective over a wide range of
concentrations, the lowest level of selenium was 35µg L −1 .
2.88.2 Ion chromatography
Hoover and Jager [666] have discussed the determination of selenate together with other
anions (selenite and arsenite) in potable and ground waters.
The application of this technique is also discussed under multianion analysis in
sections 12.2.2 and 12.2.4.
2.88.3 Preconcentration
The preconcentration of selenate is discussed in section 15.1.9.
2.89 Selenite
2.89.1 Spectrophotometric methods
Bodini and Alzamora [667] used reaction of 4,5,6-triaminopyridine with selenite in acidic
medium as the basis of Spectrophotometric method for estimating traces of the latter in
non saline water. The reaction product is a piazselenol with an absorption maximum at
362nm. The precipitate is dissolved in 3.5M phosphoric acid in order to avoid
interference from iron and chloride or tin(II). The calibration graph is linear up to 10mg
L −1 ] selenium and the detection limit is 0.1mg L −1 . The relative standard deviation is
1.5% for pure solutions. The method is accurate and precise.
2.89.2 Spectrofluorometric methods
Takayanagi and Wong [668] give details of fluorometric procedure for the determination
of tetravalent selenium in non saline waters. The optimal conditions for fluorometric
determination of total selenium were also investigated.
A method has been described [669] for the determination of selenite in non saline
waters based on the formation of piazselenols by reaction with substituted 1,2-
diaminobenzenes. The derivatives were extracted into solvents prior to analysis by
fluorometry or gas chromatography with electron capture detection, according to
published methods. The use of 1,2-diamino-3,5-dibromobenzene and 4-nitro,1,2-
diaminobenzene enabled detection limits of 1ng L −1 and 6ng L −1 selenium in water to be
achieved, respectively. Using diaminonaphthalene as a fluorometric reagent, a detection
limit of 50ng L −1 could be obtained, although at the risk of severe interference from ferric
iron, nitrite and nitrate. All organoselenium compounds could be decomposed by
ultraviolet irradiation, with formation of selenite.
2.89.3 Polarography
Lin Ahmed et al. [670] determined selenite by a polarographic technique involving the