A novel method for speciation of Cr(III) and Cr(VI) and individual determination using Duolite C20 modified with active hydrazone

Trivalent and hexavalent chromium have been successfully separated and estimated from different solutions using 1-(3,4-dihydroxybenzaldehyde)-2-acetylpyridiniumchloride hydrazone (DAPCH) loaded on Duolite C20 in batch and column modes. The obtained modified resin [DAPCH-Duolite C20] was identified by C, H and N analyses and infrared spectra. The presence of multi-active chelating sites gives the ability for DAPCH to bind more chromium, Cr(III) by forming stable complex and chromate by forming ion pair molecule [H2DAPCH-Duolite C20]2+[Cr2O7]2− (H2DAPCH-Duolite C20 is the protonated form in acidic medium). The extraction isotherms were measured at different pH. The pH was found to be the backbone for the separation procedure in which the Cr(VI) and Cr(III) ions are sorbed selectively from aqueous solution at pH 2 and 6, respectively. The sorbed ions can be eluted using different concentrations of HCl. The saturation sorption capacity (41.6 and 20.05 mg g−1), the preconcentration factor (150 and 200) and the detection limit (13.3 and 10.0 ppb) were calculated for Cr(III) and (VI). The loaded resin can be regenerated for at least 50 cycles. The utility of the modified resin was tested in aqueous samples and shows R.S.D. value of <4% reflecting its accuracy and reproducibility.