Coprecipitation procedure for speciation of chromium in some dairy food product and water samples by FAAS

A new method based on the coprecipitation procedure (CP) for separation/speciation using flame atomic absorption spectrometric (FAAS) determination was proposed for the determination of Cr(III)/ Cr(VI) in some real samples with Co(II)/α-Benzoinoxime precipitate. It enabled a very selective, basic and rapid method for chromium determination to be developed. The analytical variables including pH, amount of α-Benzoinoxime, amount of Co(II) as carrier element, and sample volume were investigated for the quantitative recoveries Cr(III)/Cr(VI). No interfering effects were observed from the concomitant ions when present in real samples. Cr(III) was quantitatively recovered on Co(II)/α-Benzoinoxime precipitate at a pH range of 7–10, while Cr(VI) was not quantitatively recovered for any of the pHs. The calibration graph was linear in the range of 1.0–10.0 mg L-1. Under the optimized conditions, detection limits of 0.01 μg L-1 and the relative standard deviations of 1.1% were found. The pre concentration factor was found to be 1000. The precipitate was dissolved in 0.1 mL of concentrated HNO3, and made up to 1.0 mL with de ionized ultra pure water. The validation of the presented CP was checked by the analysis of certified reference materials. The method was applied for the determination of Cr(III)/Cr(VI) in real samples such as natural waters and some dairy food samples, and good results were obtained (relative standard deviations <2%, recoveries >95%).