Precise δ88/86Sr determination on a MC-ICP-MS by an improved method combining Zr-empirical external normalization isobaric interference correction and 84Sr–87Sr double spike

Abstract

The natural fractionation of stable Sr isotopes (δ^88/86Sr) has attracted increasing attention as it serves as a new tracer to explore the biogeochemical process or source identification of Sr. As its applications have been expanded in various research fields, a highly efficient, accurate, and precise analytical method for δ^88/86Sr determination is bound to be needed. To date, the most accurate and precise δ^88/86Sr determination is performed by using the double spike (DS) technique in thermal ionization mass spectrometry (TIMS). However, TIMS suffers from long data acquisition time compared to multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). In this paper, we present a novel approach, combining the use of Zr isotope empirical external normalization (EEN) for Kr and Rb isobaric interference correction and ⁸⁴Sr–⁸⁷Sr DS to overcome the severe mass bias effects on the measured ⁸⁸Sr/⁸⁶Sr ratios, to improve the analytical accuracy of δ^88/86Sr determination by MC-ICP-MS. The δ^88/86Sr of the IAPSO seawater standard was determined to be 0.37‰ ± 0.03 (2SD, n = 16) with an internal precision better than ±0.01‰ (2SE). By applying this new EEN-DS MC-ICP-MS method, the accuracy is significantly improved, which is comparable to DS TIMS.