The immobilization of hydrophilic ionic liquid for Cr(vi) retention and chromium speciation

Abstract

The immobilization of N-methylimidazolium (Nmim) onto PVC surface forms bonded hydrophilic ionic liquid 1-chlorovinyl-3-methylimidazolium chloride (PVC-NmimCl), which entails anion exchange nature and positively charged surface, facilitating favorable retention of Cr(VI) with a retention capacity of 23.2 mg g⁻¹ for Cr(VI) at pH 5.6. A novel on-line solid phase extraction approach for the separation and preconcentration of Cr(VI) is developed in a sequential injection system with a PVC-NmimCl mini-column, and an extra mini-column of strong acidic styrene type cation exchange resin is incorporated for pre-eliminating Cr(III) in sample solution before entering the PVC-NmimCl mini-column. The retained Cr(VI) is effectively recovered with elution by 0.2 mol l⁻¹ NH₄NO₃ solution, and the eluate is quantified by electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma mass spectrometry (ICP-MS). With a sample volume of 2000 μl, a complete retention of Cr(VI) is obtained, giving rise to an enrichment factor of 23.4 and a sampling frequency of 9 h⁻¹. A linear range of 0.01–1.0 μg l⁻¹ for Cr(VI), along with a detection limit of 3 ng l⁻¹ and a RSD of 2.9% at 0.5 μg l⁻¹ is obtained. Total chromium in a certified reference material of reverine water (GBW08608) is determined after oxidation, which results in good agreement between the certified and the found values. The procedure is further demonstrated for chromium speciation in tap water and snow water samples.