Vanadium isotope measurement by MC-ICP-MS

• Published in: Chemical geology Vol. 421; pp. 17 - 25
• Main Authors: Wu, Fei, Qi, Yuhan, Yu, Huimin, Tian, Shengyu, Hou, Zhenhui, Huang, Fang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10-02-2016
• Subjects: Chemical separation; Geological reference materials; Isotopes; MC-ICP-MS; Polymers; Reference materials; Resins; Rocks; Vanadium; Vanadium isotope; Vanadium isotopes; Chemical separation; MC-ICP-MS; Geological reference materials; Vanadium isotope
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/j.chemgeo.2015.11.027

We present a method to measure vanadium (V) isotopic composition for terrestrial rocks in this study. Vanadium was efficiently separated from matrix elements by a chromatographic technique using cation- and anion-exchange resin columns, avoiding the expensive TRU Spec resin. Vanadium isotope ratios were measured using a Thermo Scientific Neptune Plus MC-ICP-MS employing a sample–standard bracketing method. The increase in instrument sensitivity significantly reduces the amount of V required for the isotope analysis. Potential effects of acid molarities and concentration mismatch on instrumental analyses were rigorously evaluated. In addition, we performed Cr- and Ti-doping experiments to ensure the precision and accuracy of V isotope measurement. The δ51V values of mono-elemental V standards (BDH and USTC-V) relative to an Alfa Aesar (AA) standard solution (defined as δ51V=[(51V/50V)sample/(51V/50V)AA−1]×1000) measured in our laboratory were −1.23±0.08‰ (2SD, n=197) and 0.07±0.07‰ (2SD, n=112), respectively. Analyses of synthetic standard solutions (element doping+matrix spiking) obtained the same δ51V for the pure V solutions with a precision better than ±0.1‰ (2SD). Vanadium isotopic compositions of 12 reference materials, including igneous rocks (with mafic to felsic compositions) and manganese nodules, were measured using this method. These reference materials including basalts: BCR-2, −0.78±0.08‰ (2SD, n=36); BHVO-2, −0.83±0.09‰ (2SD, n=22); BIR-1, −0.92±0.09‰ (2SD, n=52); JB-2, −0.87±0.06‰ (2SD, n=20); diabase: W-2, −0.94±0.08‰ (2SD, n=15); andesites: AGV-1, −0.71±0.10‰ (2SD, n=6); AGV-2, −0.70±0.10‰ (2SD, n=37); JA-2, −0.80±0.07‰ (2SD, n=15); quartz latite: QLO-1, −0.61±0.03‰ (2SD, n=3); granodiorite: GSP-2, −0.62±0.07‰ (2SD, n=26); and manganese nodules: NOD-P, −1.65±0.06‰ (2SD, n=10); NOD-A, −0.99±0.10‰ (2SD, n=19). Based on repeated analyses of the rock standards, the long-term external precision of our method is better than ±0.1‰ (2SD) for δ51V. Such precision allows us to identify V isotope fractionation in high-temperature terrestrial samples, suggesting that V isotope geochemistry can be more widely used to study magmatism as well as supergene processes.
•V isotope compositions of 12 reference materials were measured by Neptune plus MC-ICP-MS using a modified method.•The method significantly enhances time efficiency and reduces the amount of V required for isotope analysis.•The long-term external precision of δ51V is better than ±0.1‰ (2SD).