Flow-injection solid phase extraction using Dowex Optipore L493 loaded with dithizone for preconcentration of chromium species from industrial waters and determination by FAAS

Abstract

An online flow injection preconcentration system for speciation of Cr(III) and Cr(VI) based on the combination of solid phase extraction (SPE) and flame atomic absorption spectrometry (FAAS) has been described. A new solid phase extractor, Dowex Optipore L493 modified with dithizone was synthesized and used in a minicolumn of flow injection system. The retained Cr(III) ions from the resin were eluted with 0.1 M HNO₃ and then were introduced directly to the burner system of FAAS. The effect of experimental parameters like pH, eluent and sample flow rates on the retention of Cr(III) ions were examined. The effect of common interfering ions on the absorbance of Cr(III) ions was also examined. For preconcentration time of 120 s and sample volume of 10 mL the preconcentration factor achieved was 82, the detection limit corresponding to three times of the standard deviation of the blank was 0.13 ng mL⁻¹. The precision of the method was evaluated as relative standard deviation which was 1.13% for 100 μg L⁻¹ of Cr(III) solution. Total chromium was determined after reducing Cr(VI) to Cr(III) using hydroxylamine hydrochloride and the concentration of Cr(VI) was calculated by subtraction. The suggested method was successfully applied for spike recovery studies in industrial water samples using certified Cr(III) solution traceable to NIST. The validation of the proposed method was studied by analyzing Standard Reference Material (SRM 1643e, Trace Elements in Water) supplied by NIST, Gaithersburg, MD, USA.