Chromium speciation using task specific ionic liquid/aqueous phase biphasic system combined with flame atomic absorption spectrometry

Abstract

In this work, 1-alkyl-3-methylimidazolium based ionic liquids combined with salicylate or thiosalicylate anions as task specific ionic liquids were used to form a stable ionic liquids (IL)/aqueous biphasic systems for extraction of Cr(III) and Cr(VI) species prior to flame atomic absorption spectrometry (FAAS) determination. It was found that the 1-octyl-3-methylimidazolium salicylate was selective to extract Cr(III). The Cr(VI) content was calculated by subtracting Cr(III) from the total chromium with conversion of Cr(VI) to Cr(III) in the presence of ascorbic acid. Based on the preliminary experiments, the factors influencing phase behavior of the IL/aqueous biphasic system were investigated. The main factors affected the extraction of Cr(III) were modeled by using central composite design and optimized by using non-linear Nelder-Mead method. Under the defined optimum conditions, the calibration curves were linear over the concentration range of 40–470μgL−1 and 55–500μgL−1 for Cr(III) and total Cr, respectively. The limit of detection (3Sb/m) for Cr(III) was 7.7μgL−1. The relative standard deviations for six replicate determinations of 250μgL−1 of Cr(III) and total Cr were 5.5% and 7.6%, respectively. Finally, the proposed system has been successfully applied to the extraction and speciation of Cr in real water and urine samples.