Speciation of vanadium(iv) and (v) in mineralwater by anion exchange liquid chromatography-inductively coupled plasma mass spectrometry after EDTA complexation

Abstract

HPLC with on-line ICP-MS was used for the determination of V(IV) and V(V) in natural mineral water. Cationic and anionic tetravalent and pentavalent vanadium species were converted into V–EDTA complexes, i.e.[VO(EDTA)]²⁻ and [VO₂(EDTA)]³⁻, which could be effectively separated on a short anion exchange column in <6 min. Pre-column EDTA complexation also prevented species interconversion as a result of loss of CO₂ from samples and their exposure to atmospheric oxygen. A low-salt mobile phase (4 mM carbonate buffer and 5 mM EDTA–Na₂) compatible with ICP-MS detection was used in chromatographic separations. The method was tested on real samples spanning one order of magnitude of V concentrations and encompassing a wide range of potential interfering ions and total dissolved solids, providing accurate and reproducible results. Mass balance budgets gave a mean value of 100% (range 96–107%). Recoveries from spiking experiments were in the range 98–103%. Precision as average intra-day repeatability was 1.2% and 0.9% for V(IV) and V(V), respectively. Average inter-day repeatability was 5.5% and 1.4% for V(IV) and V(V), respectively. Limits of detections were 0.16 μg L⁻¹ for V(IV) and 0.025 μg L⁻¹ for V(V). The interference arising by ³⁵Cl¹⁶O was resolved chromatographically. V(V) was found to largely predominate in PET-bottled mineral water samples. Species distribution was consistent with theoretical predictions based on thermodynamic equilibria of vanadium in water. Overall, a rapid, sensitive, on-line method is provided which can be readily employed for monitoring purposes.