Speciation and determination of ultra-trace amount of Cr (III) and Cr (VI) using solid-phase extraction combined with dispersive liquid-liquid microextraction followed by electrothermal atomic absorption spectroscopy

Chromium is an environmental pollutant, the interest in chromium (Cr) speciation originates from widespread use of this metal in various industries such as metallurgical, refractories, and chemical [1]. While chromium (III) is an essential micronutrient for living organisms, the hexavalent species of chromium have strong mutagenic properties [2,3]. For this reason, various international environmental agencies have presented tight policy with regard to the limit of chromium concentration in drinking water [4]. A methodology based on the combination of solid-phase extraction (SPE) with dispersive liquid–liquid microextraction, using a proper chelating agent, prior to electrothermal atomic absorption spectrometry (ETAAS) has been developed for speciation and determination of ultra-trace amount of chromium in water samples. The determination of Cr(III) was achieved by selective formation of the Cr(III) complex. Total Chromium was determined similarly after reduction of Cr(VI) to Cr(III) with reduction agent and Cr(VI) concentration was calculated by difference. Parameters affecting the extraction process have been carefully evaluated. Under the optimized extraction conditions, the method attained good precisions (relative standard deviation, RSD), enrichment factors and limits of detection (LODs) that compared with other methods. The developed method was successfully applied to speciation and determination of chromium in water samples. Recoveries for spiked water samples were, in most cases, in the range of 91.3 – 103.0 %, which demonstrates the suitability of the methodology for monitoring total Cr and Cr (VI) at trace levels in water samples.