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

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 C-18 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 mu g/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 mu g/l concentration range. Relative standard deviations were 3.5 and 5.1% for Cr(VI) and Cr(III), respectively, in the determination of 50 mu g/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. (C) 1998 Elsevier Science B.V. All rights reserved.