Speciative determination of chromium(VI) and chromium(III) using flow-injection on-line preconcentration and flame atomic-absorption spectrometric detection Original Research Article

A rapid, sensitive and selective method for the speciative determination of chromium(VI) and chromium(III) in sea-water samples by flame atomic-absorption spectrometry, using on-line preconcentration on a micro-column packed with C18 bonded silica gel, has been developed. This is based on the selective formation of diethyldithiocarbamate complexes of chromium(VI) in the 1–2 pH range and chromium(III) in the 4–9 pH range in the presence of manganese(II) (which enhances the chromium(III) signal ten-fold). The preconcentrated species desorbed by methanol directly from the column to the nebulizer-burner system using a flow rate of 4.0 ml/min. Five hundred-fold enrichment of Cr(VI) and Cr(III) was observed with a detection limit of 0.02 μg/l for a 5 min preconcentration time. The effect of probable concomitant species in seawater was determined and a satisfactory recovery of 95–105% could be obtained. Linear calibration curves were obtained for both the species, Cr(VI) and Cr(III), in the 0.2–200 μg/l concentration range. Relative standard deviations were 3.5 and 5.1% for Cr(VI) and Cr(III), respectively, in the determination of 50 μg/l of each of these species. The developed procedure was found to be suitable for the determination of Cr(VI) and Cr(III) species (Cr(total)) in various sea-water samples of western and eastern coasts of India. Further, the developed procedure was successfully applied for the determination of Cr(VI) and Cr(III) species in tannery and plating-bath effluents.