Development of Analytical Procedure for the Determination of Exchangeable Cr(VI) in Soils by Anion-exchange Fast Protein Liquid Chromatography with Electrothermal Atomic Absorption Spectrometry Detection

Abstract

Analytical procedure for the determination of exchangeable Cr(VI) was developed. In order to optimise the extraction procedure, the efficiency of extraction of exchangeable Cr(VI) in soil samples was investigated in KH2PO4–K2HPO4 buffer solutions (0.015 up to 0.2 mol l−1), adjusted to the pH of the soil. Phosphate buffer was used to efficiently desorb Cr(VI) from soil particles. The extraction time (mechanical shaking) ranged from 1 up to 72 h. Cr(VI) in soil extracts was determined by anion-exchange fast protein liquid chromatography with electrothermal atomic absorption detection (FPLC-ETAAS). The study was performed on soil samples from the field treated with the tannery waste for seventeen years. Samples were analysed in the 16 year after the last waste application. It was experimentally proven that the optimal phosphate buffer concentration was 0.1 mol l−1 and extraction time 16 h. An additional experiment was done to confirm that during the extraction, soluble Cr(III) was not oxidised to Cr(VI) by Mn(IV) oxides present in soil samples. For this purpose soil with the same characteristics, but not treated with tannery waste, was spiked with Cr(III) and the analytical procedure performed. No measurable Cr(VI) concentrations were detected. The repeatability of measurement was 2.5%, while the reproducibility of measurement was 6.9%. The accuracy of the analytical procedure was tested by spiking of soil samples with Cr(VI). The recoveries were better than 95%. The analytical procedure with limit of detection (LOD) 15 ng g−1 of Cr(VI) was sensitive enough for the determination of exchangeable Cr(VI) in soils. In field soil samples analysed the concentrations of exchangeable Cr(VI) were found to be about 200 ng g−1.