Trace enrichment and ion chromatographie determination of metal oxoanions in environmental water samples

For the analysis of trace metal oxoanions using non-suppressed ion chromatography (IC), the presence of nitrite, nitrate and bromide in high quantities can seriously interfere with direct spectrophotometric detection. Similarly, direct analysis of water of high salt content like hard water will also encounter the problem of column disturbance. Sample pretreatment using a chelating resin for matrix cleanup and trace enrichment were investigated. Chelex-100 resin was found to be useful for removing common inorganic anions and retaining metal oxoanions. Recoveries of > 90% were obtained for SeO2−4, AsO3−4, MoO2−4, VO−3 and WO2−4, whereas the recovery of CrO2−4 was ca. 70%. With 40-fold preconcentration, the detection limits for some of the oxoanions could be lowered to sub-ng ml−1 levels. Well separated peaks and no interferences were observed for the analysis of environmental water samples using the new IC procedures and the results compared favourably with those obtained by atomic absorption spectrometry.