Precise determination of δ88/86Sr in natural samples by double-spike MC-ICP-MS and its TIMS verification

Abstract

δ88/86Sr values of standards and a variety of natural samples were measured by MC-ICP-MS using the double-spike (DS) method and compared to results obtained by the standard-sample-bracketing (SSB) method and to DS-TIMS measurements. The external reproducibility of the SRM987 measurements carried out by DS-MC-ICP-MS was 0.021‰ (1SD), slightly better than previously published DS-TIMS and SSB-MC-ICP-MS results. The value of the IAPSO seawater standard (0.388 ± 0.018; 2SEM) agrees with the results of the current SSB and DS-TIMS measurements and with previously published values. Using these values a variance-weighted mean for seawater was calculated (0.387 ± 0.002, 2SEM). Compared to measurements carried out by the SSB method, natural sample measurements by the DS method are more accurate and more precise. An excellent agreement between DS-MC-ICP-MS and DS-TIMS methods was demonstrated for δ88/86Sr determination in natural samples over a range of ∼0.5‰. The DS-TIMS δ88/86Sr results had a smaller standard error than the DS-MC-ICP-MS measurements but required a much longer acquisition time.