Speciation Analysis for Chromium(III) and Chromium(VI) after Micro Solvent Extraction with in situ Extractant Formation Method

A simple and selective method for the speciation of sub mu g/L levels of inorganic chromium species in water sample is described. The proposed method is based on micro solvent extraction with an in situ extractant formation method and graphite furnace atomic absorption spectrometry. By mixing carbon disulfide and pyrrolidine in xylene prior to use, pyrrolidinedithiocarbamic (PDC) acid forms. The extraction behavior of Cr(III) and Cr(VI) caused by a variation of the pH and composition of a mixed solvent was investigated. At pH 3.0, Cr(VI) was selectively extracted from co-existing Cr(III) as a PDC complex. At pH 6.0, both Cr(III) and Cr(VI) were simultaneously extracted into the organic phase after heating at 35 degrees C for 30 min. A 20 mu L aliquot of the organic phase was injected into a graphite furnace. Under a 50-fold pre-concentration factor by using 25 mL of water samples, linear calibration curves of Cr(VI) and total Cr [Cr(III)] were obtained over the range of 0 to 0.4 mu g/L and 0 to 0.5 mu g/L with detection limits (3 sigma) of 0.75 ng/L and 0.64 ng/L. The relative standard deviations (n = 10) were 1.8% and 3.4% for 0.16 mu g/L of Cr(VI) and Cr(III), respectively. The proposed method was successfully applied to mineral water, river water and spiked samples .