Speciation of chromium metal ions by RP-HPLC.

A high-performance liquid chromatographic method with UV detection, based on chelation with morpholine-4-carbodithioate (MDTC), has been developed for the speciation of chromium. Simultaneous preconcentration of Cr(III) and Cr(VI) in aqueous solutions was achieved by extraction of metal species in chloroform as MDTC complexes. The separation of MDTC chelates of Cr(III) and Cr(VI) was realized on a C18 column with the use of acetonitrile-water (70:30) at a flow rate of 1.0 mL/min. The Cr(III) showed a single peak in chromatogram due to Cr(MDTC)(3), and Cr(VI) showed two peaks due to the formation of Cr(MDTC)(3) and Cr(MDTC)(2)(OMDTC). These two complexes were separated with different retention times at 5.4 and 4.3 min, respectively. The developed method can be used for rapid routine determination of chromium species with high precision and reliability. The method was validated by applying to various synthetic binary mixtures prepared by spiking Cr(III) and Cr(VI) in tap water.