Rapid determination of the 87Sr/86Sr ratio in water samples using ICP-MS/MS without concentration matching and matrix matching

Abstract

We present a rapid method for determining the ⁸⁷Sr/⁸⁶Sr ratio in water samples using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) in the oxygen reaction mode, thus eliminating the need for Sr purification. With O₂ as the reaction gas, Sr⁺ ions undergo a mass shift, measured at m/z 102 and 103. Our investigation into the interference elimination, concentration effects, and matrix effects revealed that the ⁸⁷Sr/⁸⁶Sr determination method is robust, yielding a value of 0.7101 ± 0.0010 (2SD) for the NIST SRM 987 standard, consistent with the reference value of 0.71034 ± 0.00026 (2SD). This accuracy was maintained even with a Rb/Sr ratio of 100. Further, this method was insensitive to the concentration ratio of Sr in the sample and standard (from 0.1 to 10) and exhibited negligible sample matrix effects, as shown by the average values for an IAPSO seawater standard, calibrated with pure Sr and matrix-matched Sr standard solutions, yielding ⁸⁷Sr/⁸⁶Sr ratios of 0.7091 ± 0.0006 (2SD) and 0.7092 ± 0.0008 (2SD) respectively, which were consistent with the literature values. Subsequently, real water samples were analyzed using the proposed method, yielding good results.