Rapid Two-Column Separation Method For Determining Barium Isotopic Compositions Using MC-ICP-MS

Abstract

: In recent years, the stable isotope composition of barium has emerged as a powerful tracer for understanding crucial geo-social processes; therefore, it is necessary to develop an efficient method for Ba isotopic ratios. Herein, we describe a rapid method for determining the isotopic ratios of Ba using a multi-collector inductively coupled plasma mass spectrometer in the low-resolution mode (Neptune Plus). In this method, the exact amount of the resin and the low eluted volume of the acid used in column purification significantly reduce the time required for Ba separation. Instrumental mass bias calibrations were performed for both standard-sample bracketing (SSB) and double-spike methods. The results show that the double-spike method provided Ba isotopic ratios with higher precision than the SSB technique. The effects of acid molarity and concentration mismatch, as well as the potential matrix effect, were investigated in the wet plasma mode. We evaluated the Ba isotopic compositions of ten geological reference materials, namely, BCR-2, BHVO-2, AGV-2, GSP-2, RGM-2, G-2, GSR-3, GSR-5, GSR-8, and GSR-11. Results indicated that these compositions were highly accurate with respect to the international Ba isotope standard, NIST SRM 3104a. Furthermore, the Ba isotopic compositions of most geological reference materials examined in this study agreed well with previously published data within the quoted analytical uncertainties. The long-term reproducibility analyses of all standards indicated that the obtained isotopic ratios were highly reproducible for δ 138/134 Ba, with precisions of ≤ ±0.05‰ (2SD). Compared to previous reports, we optimized the process of chemical purification, separated Ba samples faster, and improved the efficiency of the analyses employed in this study.