Preconcentration method on modified silica fiber for chromium speciation

A new method involving pre-concentration on modified silica fiber is described for the speciation of chromium(III) [Cr(III)] and chromium(VI) [Cr(VI)] in aqueous media. This method is based on the different chelating behavior of Cr(III) and Cr(VI) with morpholine-4-carbodithioate (MDTC). Both complexes are extracted on silica fiber modified by sol-gel technology by using 3-aminopropyltriethoxysilane (APS) as a precursor. All extracted samples are directly injected into an high-performance liquid chromatography injector for the simultaneous determination of Cr(III) and Cr(VI). Cr(VI) forms two different complexes, and Cr(III) forms a single complex with MDTC. Therefore, the concentration of Cr(VI) is determined directly from the peak area obtained at 5.4 min; whereas, the assay of Cr(III) is based on subtracting the peak area of Cr(VI) from the total peak area obtained at 4.3 min. Under the optimized conditions, the limits of detection for Cr(III) and Cr(VI) are found to be 0.7 ng/mL and 0.2 ng/mL, respectively.