Determination of Valences of As, Cr, Sb and Se in Soil Using HPLC-HG-AFS

BACKGROUND The environmental effects of heavy metal pollutants in soil are closely related to their inorganic valence. The determination of the valences of As, Cr, Sb and Se elements is of great significance, but due to the easy conversion between the valences, the determination is difficult and the degree of standardization is low. The geological industry standard DD2005-3 recommends the use of ion exchange resin separation, atomic fluorescence spectrometry to determine the valences of As, Sb, and Se, and graphite furnace atomic absorption spectrometry (GFAAS) to determine the valence of Cr. The preparation of these methods is cumbersome, the number of measurements is large, the workload is large, and the existence of other element forms can also cause errors in the results. OBJECTIVES To establish a set of methods suitable for determining the valences of water-soluble and exchangeable As, Cr, Sb and Se in soil samples. METHODS The valences of As, Sb and Se were separated and determined by HPLC-HG-AFS after 30 min extraction in a water bath of 50℃. The processes were simpler and more accurate than the recommended subtraction processes by AFS. To avoid the masking action of some extracting agent, the method of selective determination of Sb(Ⅲ), Sb(Ⅴ), Se(Ⅳ) and Se(Ⅵ) by AFS was developed, which has the advantage of low instrument cost. As for Cr(Ⅲ) and Cr(Ⅵ), after separation by ion-exchange resin, they were determined by ICP-MS, which has higher sensitivity than the recommended GFAAS. RESULTS The detection limits of As(Ⅲ), As(Ⅴ), Cr(Ⅲ), Cr(Ⅵ), Sb(Ⅲ), Sb(Ⅴ), Se(Ⅳ) and Se(Ⅵ) was ≤ 0.02μg/g, with the RSD of 3.8%-10.7% and the recovery of 91.0%-106.0%. These methods were successfully applied to the analysis of geological samples, and all indices met the quality requirements of DD2005-3. CONCLUSIONS Compared with non-chromatographic methods, newly established methods by HPLC-HG-AFS can determine multiple components simultaneously. At the same time, preliminary studies have shown that the valence content of elements in the soil is not high, and lacks correlation with the total amount of soil.