Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 126

2.16 Chlorate
2.16.1 Titration methods
Chlorate ion concentration at the sub mg L −1 level has been measured with high precision
and accuracy by a iodometric method [163]. The chlorate is reduced by iodide ion in 6M
hydrochloric acid:
Oxidation of iodide ion by air is prevented from removing the air with pure hexane and
scrubbed nitrogen. Saturated disodium phosphate was used to neutralise the acid. The
iodometric endpoint was detected either with thyodene as the indicator or the colour of
iodine in the hexane layer. The precision of the method is better than 1%. For
concentrations of chlorate below 3.5 mg L −1 potentiometric titration is recommended.
2.16.2 Flow injection analysis
Miller et al. [164] have described two approaches to the determination of trace levels of
chlorate ion based on the reaction of chlorate ion with iodide to produce iodine. High
hydrochloric acid concentrations accelerated the reaction. Flow injection analysis, which
excluded air from the flow stream, was used. The first method could detect chlorate ions
at levels of 10µM and the second method, using a stopped flow condition, could detect
levels of 1µM.
2.16.3 Ion chromatography
The application of this technique is discussed under multianion analysis in section 12.2.5.
2.16.4 High performance liquid chromatography
The application of this technique is discussed under multianion analysis in sections
13.1.1.5 and 13.1.1.7.
2.17 Chloride
Titration methods for the determination of halides are convenient but limited in
sensitivity or ability to automate. When these characteristics are required, then
spectrophotometric or titration or ion selective electrode methods are recommended.
Methods based on ion selective electrodes are also useful. When mixtures of anions are to
be analysed and high sensitivity and speed are essential, then ion chromatography
becomes the method of choice.