Dispersive liquid-liquid microextraction combined with electrothermal atomic absorption spectrometry for the speciation of chromium in environmental samples

Abstract

A new method for the speciation of chromium by dispersive liquid-liquid microextraction (DLLME), combined with electrothermal atomic absorption spectrometry (ETAAS), is presented and evaluated. Since Cr(III) forms complexes with Nbenzoyl-N-phenylhydroxylamine (BPHA) at pH 9.0, it was extracted into fine droplets of carbon tetrachloride (extraction solvent) with ethanol in aqueous solution, while Cr(VI) remained as free species in aqueous solution. After centrifugation, Cr(III) was determined in the sedimented organic phase. Cr(VI) was reduced to Cr(III) with hydrogen peroxide prior to the total determination of Cr, which was based on subtracting Cr(III) from total chromium. Under the optimized conditions and after extraction, the limit of detection (LOD) for Cr(III) was 0.01 ng mL-1, with an enrichment factor of 96. The relative standard deviation (RSD) for seven replicate determinations of 1.0 ng mL-1 Cr(III) was 4.7%. The developed technique was applied to the speciation of chromium in real water samples and the recoveries for the spiked samples were in the 94.5-107.1% range. For validation, two certified reference materials of water samples (GBW08607 and GBW08608) were analyzed, and the results obtained were in good agreement with the certified values.