Cloud point extraction combined with graphite furnace atomic absorption spectrometry for speciation of Cr(III) in human serum samples.

A cloud point extraction (CPE) method for the preconcentration of ultra-trace chromium speciation in human serum samples prior to determination by graphite furnace atomic absorption spectrometry (GFAAS) had been developed in this paper. In this method, Cr(III) reacts with 1-(2-pyridylazo)-2-naphthol (PAN) yielding a hydrophobic complex, which is then entrapped in the surfactant-rich phase, whereas Cr(VI) remained in aqueous phase. Thus, separation of Cr(III) and Cr(VI) could be realized. Total chromium was determined after the reduction of Cr(VI) to Cr(III) by using ascorbic acid as reducing reagent. PAN was used not only as chelating reagent in CPE, but also as chemical modifier in GFAAS. Triton X-114 non-ionic surfactant had been used as an extraction medium. The main factors affecting CPE efficiency, such as pH of solution, concentration and kind of complexing agent, concentration of non-ionic surfactant, equilibration temperature and time, were investigated in detail. An enrichment factor of 83.5 was obtained for the preconcentration of Cr(III) with 10 mL solution. Under the optimal conditions, the detection limit of Cr(III) was 0.02 μg L⁻¹. The relative standard deviation was 2.6% for intra-day assay precision (n=7, c=10 ng mL⁻¹), values of recovery for chromium were from 92.0% to 94.7% for three samples. This method is simple, accurate, and sensitive and can be applied to determine ultra-trace chromium speciation in human serum.