First order speciation of vanadium and chromium in water samples by on-line continuous membrane separation hyphenated to inductively coupled plasma mass spectrometry

An on-line anion-exchange membrane separation system has been coupled to inductively coupled plasma mass spectrometry (ICP-MS) for the total vanadium(V) and chromium (Cr) determination and V(IV) and Cr(III) species determination simultaneously. The positive charged V(IV) and Cr(III) species have been efficiently separated from V(V) and Cr(VI), and selectively determined by the on-line electrodialyzer-ICP-MS. To determine the total concentrations of V and Cr in water samples, H2SO4 and Na2S2O3 were added to convert all vanadium and chromium species into their positive species, thus, V(V) and Cr(VI) in the samples were quantified by subtraction. The cool plasma and reaction gas can also be avoided as the severe interference from chloride, carbon and nitrogen-based molecular ion has been substantially suppressed by the anion-exchange membrane. The detection limits of the analytes were 0.02 mu g L-1 for V(IV) and 0.06 mu g L-1 for Cr(III) with this on-line system, respectively, and the relative standard deviation (n = 10) of 10 mu g L-1 V(IV) and Cr(III) were 3.7% and 2.1%, respectively. The developed method has been applied for the speciation of V and Cr in three water samples, with V(V) and Cr(III) found as the main species in these samples. The accuracy and feasibility of this method have also been verified by spike tests and a certified reference material (CRM) of environmental water (GSBZ 50029-94) and a CRM of riverine water (GBW 08608), good recoveries have been obtained and the analytical results are also in good agreement with the certified values.