Determination of Precise and Accurate 51V/50V Isotope Ratios by MC-ICP-MS, Part 1: Chemical Separation of Vanadium and Mass Spectrometric Protocols

We present the first technique to obtain precise and accurate vanadium (V) stable isotope compositions by chemical isolation and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Separation of V from matrix elements was achieved via five separate ion exchange columns. The procedure quantitatively removed Ti and Cr, which contain direct isobaric interferences on the minor isotope V-50. Isotope compositions were determined using a conventional standard solution-sample bracketing technique. The V isotope composition for an in-house secondary standard solution from BDH Chemicals was delta V-51 = -1.19 +/- 0.12% (2s, n = 600), measured as the per mil deviation relative to the composition of a widely available Specpure Alfa Aesar (AA) vanadium solution. This represents an improvement in measurement precision on previous techniques of almost two orders of magnitude. The effects of adding Cr, Ti and S to standard solutions were explored to determine the robustness of protocols. Only very low levels of these elements could be tolerated to obtain precise and accurate isotope compositions and was achieved with the chemical purification procedure. Standard solutions from AA and BDH processed as unknowns through the entire chemical separation and measurement protocols returned 100% yields and the same isotopic compositions as those of unprocessed standard solutions.