Simultaneous speciation of inorganic chromium(III) and chromium(VI) by hollow-fiber-based liquid-phase microextraction coupled with HPLC-UV.

The speciation of chromium(VI) and chromium(III) was investigated by using hollow fiber liquid-phase microextraction based on two immiscible organic solvents followed by high performance liquid chromatography with ultraviolet detection. In this method, chromium(VI) and chromium(III) reacted with ammonium pyrrolidine dithiocarbamate to produce hydrophobic complexes. Subsequently, the complexes were first extracted into a thin layer of organic solvent (n-dodecane) present in the pores of a porous hollow fiber, and then into a μL volume of an organic acceptor (methanol) located inside the lumen of the hollow fiber. Then, the extracting organic phase was injected into the separation column of the high-performance liquid chromatograph for the analysis of both chromium species. Effective parameters on extraction were optimized using one-variable-at-a-time method and central composite design. Under optimized conditions, a linear range of 0.25-100 and 0.5-100 μg/L (R > 0.998), the limits of detection of (S/N = 3) 0.08 and 0.1 μg/L and a preconcentration factor of 625 and 556 were achieved for chromium(VI) and chromium(III), respectively. The method was successfully applied to the speciation and determination of chromium species in different water samples and satisfactory results were obtained.