Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 273

2.86 Resorcylate
2.86.1 Ion chromatography
The application of this technique is discussed under multianion analysis in section 12.2.5.
2.87 Salicylate
2.87.1 Ion chromatography
The application of this technique is discussed under multianion analysis in section 12.2.5.
2.88 Selenate
In recent years, there has been increasing interest in the trace determination of selenium
because of its dual role as an essential nutrient at low concentration levels and as a toxic
substance at higher concentration levels. Selenium deficiency, for example, can be related
to necrotic degeneration of the liver, pancreas, heart and kidney. High selenium
concentrations can establish toxicity phenomena like inflammation of the feet, softening
and loss of hoofs and horns in animals, or loss of hairs and nails and irritation of skin and
eyes in humans. The narrow concentration range between the two contrary effects
requires precise knowledge of the selenium content in the environment. The accurate
determination of selenium, however, is still a major challenge for analysts.
Detailed information about the availability and mobility of an element in the
environment and its behaviour in biological and geochemical systems, however, requires
the additional knowledge of the different chemical forms in which the element exists.
Species determination with respect to selenium, which can exist in different oxidation
states (−2, selenide; 0, elemental selenium; +4, selenite; +6, selenate) and multiple
chemical forms within the oxidation state −2 (eg organic and inorganic selenide), is
especially important in aquatic systems, because the occurrence of selenium is mainly
influenced by its chemical form. Therefore, analytical methods that can provide such
information are receiving more attention.
2.88.1 Differential pulse polarography
Brimmer et al. [665] investigated the quantitative conversion of selenate in aqueous
solution to selenite prior to determination by differential pulse polarography. Calibration
curves of peak current against selenite concentrations of 2-15mg L −1 with 0.12-3.0M
hydrogen chloride solution as background electrolyte showed a good linear relationship
which was consistent with results using standard solutions. Kinetic analysis indicated that
the reaction was first order with respect to selenate and that the reaction rate increased
with increasing hydrogen chloride concentration. The procedure was used to detect