Cr(III)/Cr(VI) speciation in water samples by extractive separation using Amberlite CG-50 and final determination by FAAS

A simple and sensitive method has been developed for speciation and preconcentration of trace amounts of Cr(III) and Cr(VI) in water samples using Amberlite CG-50. The Cr(III) content of the sample solutions was sorbed on the resin at pH of 5.5, desorbed by 3% H2O2 at pH of 9.5 and then determined by FAAS. After reduction of Cr(VI) to Cr(III) by K2SO3 at pH of 3, the total chromium was determined, and the Cr(VI) was obtained by difference. The optimum conditions for reduction and sorption/desorption processes were investigated on several experimental parameters, such as pH of sample and eluent, contact time, the resin quantity, type of the reductant, eluent, and their concentrations. No considerable interferences have been observed due to the presence of a number of anions and cations, which may be found in the natural water samples. The dynamic range for the determination of both Cr(III) and Cr(VI) was found to be 2.0 x 10(-7) to 2.0 x 10(-6) M. By repeating the treatment (n: 7) with the solutions of 1.00 x 10(-6) M Cr(III) and the blanks, the relative standard deviation (RSD) and detection limit (DL) were 2.56% and 8.00 x 10(-8) M, respectively. This method has been successfully applied for the determination of the chromium species in various natural water samples. The recoveries for the spiked amounts of chromium species to the water samples were found to be more than 95% at the 95% confidence level, which satisfactorily confirmed the reliability of the method.