DETERMINATION OF CHROMIUM(III) AND CHROMIUM(VI) IN WATER USING FLOW-INJECTION ONLINE PRECONCENTRATION WITH SELECTIVE ADSORPTION ON ACTIVATED ALUMINA AND FLAME ATOMIC-ABSORPTION SPECTROMETRIC DETECTION

A rapid and sensitive method for the species-selective determination of chromium(III) and chromium(VI) in water samples by flame atomic absorption spectrometry using on-line preconcentration on a microcolumn packed with activated alumina (acidic form) has been developed. Sequential species-selective sorption was possible by using the Clark-Lubs buffer systems with pH 7 for Cr(III) and pH 2 for Cr(VI). The preconcentrated species were eluted directly from the column to the nebulizer-burner system using 1.0 mol/L nitric acid and 0.5 mol/L ammonia for Cr(III) and Cr(VI), respectively. The retention efficiency was better than 80% for Cr(III) and better than 90% for Cr(VI), giving a sensitivity enhancement of 25 for a 3-mL sample loading. The effect of concomitant species was investigated, and satisfactory recovery of 90-106% could be obtained from natural water samples. Linear calibration for both species was established over the concentration range 10-200 mug/L with detection limits (3 s) of 1.0 and 0.8 mug/L for Cr(III) and Cr(VI), respectively.