Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 478

carbon dioxide in some potable water samples. Fig. 7.5 shows the ion exclusion
chromatograms obtained before and after a softening treatment. The results indicated that
the method is useful in the field of water quality control of water treatment facilities.
Environmental waters such as river, lake and well waters were analysed for carbon
dioxide and bicarbonate by the three column ion exclusion method without any difficulty.
It may be possible to use the first peak to estimate the total salts of strong acids (such as
chloride and sulphate) in water samples. The detection limit for bicarbonate was about
2µM and the relative standard deviation about 1%.
Strong acids and salts of strong acids, which are converted to acids by the separation
column, pass rapidly through ion exchange columns and do not interfere with the carbon
dioxide/bicarbonate peak which elutes later. The effect of weak acids or salts of weak
acids was determined by adding various carboxylic acids to samples containing a known
amount of sodium bicarbonate. Fig. 7.5 shows chromatograms obtained by the one-
column, two-column and three-column ion exclusion methods. No interference was
observed from equal molar amounts of formic, acetic or butyric acids. Propionic acid has
almost the same retention time as carbonic acids and therefore constitutes an interference.
Oxalic, tartaric, citric, lactic, malic and malonic acids elute before carbonic acid and
therefore do not interfere.
7.5 Bromate
7.5.1 High performance liquid chromatography
The application of this technique is discussed under multianion analysis in section
13.1.2.1.
7.6 Bromide
In studies of the formation of bromoform produced during the disinfection of water
supplies it is necessary to have methods capable of determining bromide at the µg L −1
level.
7.6.1 Spectrophotometric method
Moxon and Dixon [9] have described an automated method for the determination of µg
L −1 amounts of bromide in potable water which is based on the catalytic effect of the
bromide ion on the oxidation of iodine to iodate by permanganate and colorimetric
measurement of residual iodine in carbon tetrachloride. A Technicon AutoAnalyser 1 is
used. The system is kept at 0±0.2°C using an insulated ice bath. An automatic chloride
method of similar sensitivity, accuracy and reproducibility is used to estimate chloride
interference. The detection limit of the method is 4µg L −1 and the precision is of the order
of 6%.
For most potable waters the effects of interferences except for that of chloride will be