A novel non-chromatographic strategy for the sequential/simultaneous extraction and analysis of chromium species by electrothermal atomic absorption spectrometry in effluents and different water sources

Abstract

A novel surfactant assisted dispersive liquid–liquid microextraction based on the solidification of floating organic drop procedure is developed for the sequential and simultaneous pre-concentration of Cr(III) and Cr(VI) from tap, river, ground and wastewaters. The sequential extraction is based on the selective formation of extractable complexes of Cr(III) with the reactive head group solubilising sites of the dispersible dodecyl benzene sulfonate surfactant, in the presence of Cr(VI). The extracting, 1-undecanol pre-concentrates the formed extractable Cr(III) from the bulk aqueous solution and solidifies it on lowering the temperature. Cr(VI) present in the aqueous solution is subjected to a similar extraction procedure after the addition of diphenylcarbazide. In the simultaneous extraction, both the species are extracted by adapting a similar extraction procedure after the addition of diphenylcarbazide and surfactant to fresh aliquots, to determine the total chromium content. The chromium concentrations in the 1-undecanol phases are determined using continuum source ETAAS (Electrothermal Atomic Absorption Spectrometry). The parameters affecting the process are optimized. Under the optimized conditions, the pre-concentration factors and limits of detections for Cr(III) and Cr(VI) in sequence and total Cr in simultaneous extractions are 25, 50 and 40; and 3, 1 and 4 pg mL⁻¹, respectively. The recoveries are in the range of 94–99% at 50–400 pg mL⁻¹ for Cr(III) and Cr(VI). The accuracy of the procedure is validated by comparing the sum of the concentrations of each individual species obtained from the sequential extraction with total chromium obtained in the simultaneous extraction procedure applied to certified reference materials such as the BCR 713 effluent, BCR 714 influent and NIST 1643c water and water samples.