Preconcentration and determination of chromium species by cloud point extraction-flame atomic absorption spectrometry

We have developed a new method for the determination of trace chromium species by flame atomic absorption spectrometry after preconcentrative separation of Cr(III) by cloud point extraction using alizarin-3-methyliminodiacetic acid as the complexing agent. The effect of pH, the amounts of complexing agent and surfactant, equilibration temperature and time was investigated systematically. Under the optimized conditions, the calibration graph of Cr(III) was linear in the range of 4-200 mu g L-1 The detection limit for Cr(III) was 1.0 mu g L-1. The relative standard deviation was 4.8% for 100 mu g L-1 of Cr(III) (n = 9). The enhancement factor was 40.05. After reduction of Cr(vi) to Cr(III) with ascorbic acid, the system was applied to determine total chromium. Cr(vi) was then calculated as the difference between the content of total Cr and the Cr(III). The proposed method has been applied to determine water samples and water-soluble chromium species in soil with the recoveries of Cr(III) and Cr(vi) spiked in samples from 94.6% to 108% and 95% to 113%, respectively.