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
The natural fractionation of stable Sr isotopes (δ88/86Sr) 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 δ88/86Sr determination is bound to be needed. To date, the most accurate and precise δ88/86Sr 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 δ88/86Sr determination by MC-ICP-MS. The δ88/86Sr 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.