Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 683

Table 12.25 Comparison of ion chromatographic and spectrophotometric analyses for
bromide

Bromide (µg L −1 )

City I.D. No Date Ion chromatography Spectrophotometer

1 3/27/81 7.5 11.6

2 9/22/81 29.6 30.9

3 12/17/80 104.7 109.8

4 10/16/80 42.6 42.9

5 7/24/81 55.8 55.4

Source: Reproduced with permission from Elsevier Science [71]

In the presence of 100mg L −1 chloride, there was 100% recovery of 80µg L −1 bromide.
Chloride was not expected to interfere with the elution of bromide at any concentration
since bromide is held preferentially over chloride by the concentrator column. In the
presence of 100mgL −1 nitrate only 16.2% of the bromide was recovered indicating the
concentrator's preference for the nitrate ion. There was no response for 80µg −1 bromide

in the presence of 1000mg L −1 sulphate, indicating 0% recovery.
Evaluation of µ-equivalent concentrator capacity yielded 8.5, 10.6, 6.8, 13.9, 11.7 and
14.6 for the 6 columns subjected to analysis. Evaluation of the concentrator found to
possess the highest µ-equivalent capacity (14.6) for percent recoveries of 80µg L −1
bromide in the presence of varying amounts of nitrate and sulphate revealed that nitrate in
excess of 17mg L −1 was found to interfere with the elution of bromide and that sulphate
in excess of 25mg L −1 was found to interfere with the elution of bromide.
Table 12.25 shows a comparison of bromide determinations obtained by the ion
chromatographic method and a spectrophotometric method based on the catalytic effect
of bromide on the oxidation of iodide or iodine to iodate by potassium permanganate in
acidic solution.
A direct statistical comparison of the two methods reveals that, for standard solutions
of 20, 60 and 100µg L −1 , the spectrophotometric method produces standard deviations of
0.37, 0.97 and 0.21 and RSDs of 1.9, 1.6 and 0.2%, while the ion chromatography
method produces a standard deviation of 1.5 and a RSD of 3.0% for 50µg L −1 bromide.
Analysis of several raw waters by both methods yielded comparable results on four out
of five samples.
Detection by the ion chromatographic method is subject to interference by excessive
levels of nitrate and sulphate but this is readily avoided by altering the concentration
volume accordingly.