SPECIATIVE DETERMINATION OF CHROMIUM(VI) AND CHROMIUM(III) USING FLOW-INJECTION ONLINE PRECONCENTRATION AND FLAME ATOMIC-ABSORPTION SPECTROMETRIC DETECTION

A rapid, sensitive and selective method for the speciative determinati on of chromium(VI) and chromium(III) in sea-water samples by flame ato mic-absorption spectrometry, using on-line preconcentration on a micro -column packed with C-18 bonded silica gel, has been developed. This i s 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 r ange in the presence of manganese(II) (which enhances the chromium(III ) signal ten-fold). The preconcentrated species desorbed by methanol d irectly from the column to the nebulizer-burner system using a flow ra te of 4.0 ml/min. Five hundred-fold enrichment of Cr(VI) and Cr(III) w as observed with a detection limit of 0.02 mu g/l for a 5 min preconce ntration time. The effect of probable concomitant species in seawater was determined and a satisfactory recovery of 95-105% could be obtaine d. 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 sta ndard deviations were 3.5 and 5.1% for Cr(VI) and Cr(III), respectivel y, in the determination of 50 mu g/l of each of these species. The dev eloped procedure was found to be suitable for the determination of Cr( VI) and Cr(III) species (Cr(total)) in various sea-water samples of we stern and eastern coasts of India. Further, the developed procedure wa s successfully applied for the determination of Cr(VI) and Cr(III) spe cies in tannery and plating-bath effluents. (C) 1998 Elsevier Science B.V. All rights reserved.