Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 479

negligible. Some contaminated drinking waters can contain elements such as iron and
manganese in amounts which could give substantial interference and these could be
diluted to a level where the interference was removed.
Based on the bromine contents, bromide, and bromate give the same response in this
technique indicating that bromide and bromate have a similar catalytic activity. Excellent
precision data were obtained for this procedure, coefficients of variation ranging from
2.2% at the 100µg L −1 level to 7.0% at the 5µg L −1 bromide level. Spiking experiments
gave recoveries between 98 and 103%, ie excellent accuracy.
7.6.2 Ion chromatography
Morrow and Minear [10] have developed an ion chromatographic procedure using a
concentrator column to improve sensitivity. This analysis, which was carried out on a
Dionex model 125 ion chromatograph equipped with concentrator column in place of an
injection loop, coupled with an auto-sampler, allowed detection at the µg L −1 level. A
concentrator column is a short separator column used to strip ions from a measured
volume of matrix leading to a lowering of detection limits by several orders of
magnitude. The concentrated sample was flushed into the system using 0.003M sodium
bicarbonate/0.0024M sodium carbonate eluant.
When using conventional ion chromatographic separation techniques, it is possible that
other matrix anions also common to non saline waters may coelute with bromide. For
example, bromide and nitrate elute simultaneously using a standard anion separator
column (Dionex No. 30065), standard anion suppressor (Dionex No. 30366) and standard
eluant (0.003M sodium bicarbonate/0.0024M sodium carbonate).
A representative chromatogram is shown in Fig. 7.6(a).
Separation of bromide from all other matrix anions was shown to be possible using a
trace anion separator (Dionex No. 30827), a standard anion suppressor and slightly
weakened standard eluent. A chromatogram is presented in Fig. 7.6(b).
Chloride, nitrate and sulphate were the only ions found to be present in any significant
quantities in the representative raw waters analysed. To determine whether response for
bromide remained the same regardless of the concentration of these anions, recovery tests
were performed on bromide standard solutions of 80µg L −1 spiked with varying
concentrations of chloride, nitrate and sulphate, using the concentrator found to have the
highest µ-equivalent capacity. 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 100mg L −1 nitrate only 16.2% of the bromide
was recovered, indicating the concentrator's preference for the nitrate