Simultaneous speciation of chromate, arsenate, molybdate and vanadate in alkaline samples by HPLC-ICP-MS at different concentration levels of vanadate†
Flay ash, cement and electric arc furnace (EAF) dust are frequently mixed in building composites. From them, chromium (Cr), arsenic (As), molybdenum (Mo) and vanadium (V) may be leached. Concentrations of V in leachates may be significantly higher than those of Cr, As and Mo, making simultaneous speciation analysis particularly difficult. In this work, a high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) procedure was used for simultaneous speciation of chromate, arsenate, molybdate and vanadate. First, the behaviour of Cr, As, Mo and V species in different oxidation states was studied during their separation under acidic (pH 5) and alkaline (pH 12) conditions. At alkaline pHs chromate, arsenate, molybdate and vanadate were simultaneously separated and eluted at retention times from 390 to 450 s, 230 to 270 s, 340 to 430 s and 270 to 380 s, respectively and detected on-line by ICP-MS, recording m/z 52, 75, 95 and 51, respectively. When V species were leached in significantly higher concentrations than Cr, Mo and As, their detection was possible at the low abundance (0.25%) 50V isotope, which is also the mass of the 50Cr isotope (abundance 4.345%), due to selective separation between V and Cr species. Good repeatability of measurement (RSD better than ±3.0%) and quantitative elution of elemental species (column recoveries 99–105%) were obtained. Finally, the procedure was applied in the simultaneous speciation analysis of chromate, arsenate, molybdate and vanadate in highly alkaline aqueous leachates from composites consisting of fly ash, cement and EAF dust that contained a wide range of concentrations of vanadate.