Separation and preconcentration of chromium species by selective absorption on Lemna minor and determination by slurry atomisation electrothermal atomic absorption spectrometry

A novel method for the separation and preconcentration of Cr(III)/Cr(VI) wi th Lemna minor and determination by slurry atomization electrothermal atomi c absorption spectrometry (ETAAS) was developed. A sample Solution was adde d to a polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna m inor, adjusted to pH 1.0, stirred for 8 min for selective absorption of Cr( III) and then centrifuged. The upper layer of solution was transferred into another polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 5.0, stirred for 12 min for adsorption of the residu al Cr(VI) and centrifuged. The two residues in two centrifuge tubes were wa shed twice with water, 2 ml of agar solution added, stirred for 2 min, then two slurries were prepared and used for the determination of Cr(III) and C r(VI) by ETAAS. Detection limits (3 sigma) of 0.01 mug L-1 for Cr(III) and 0.03 mug L-1 for Cr(VI) were obtained. The relative standard deviation was 2.8% for Cr(III) and 3.3% for Cr(VI) at the 1 mug L-1 level. The method was applied to the determination of Cr(III)/Cr(VI) in water samples. The analy tical recoveries of Cr(III) and Cr(VI) added to samples were 97-102 and 96- 103%, respectively.