A new method has been developed for the accurate, precise and more rapid determination of boron isotopes (δ11B) by MC-ICP-MS applicable to seawater and pore water samples. Obvious matrix effects have been observed when applying pure standard solutions to bracket the untreated pore water samples and matrix-containing standards. The matrix effects were eliminated by applying matrix-matched standards to measure the matrix-matched ones. The concentration effect of boron has also been investigated and it shows that boron does not exhibit an obvious concentration effect in the concentration range of 50 μg L−1 to 300 μg L−1. Therefore, IAPSO (seawater) was used as the standard to directly measure the untreated pore water and the results are satisfactory. The salient advantage of this method is that there is no need for boron purification procedures and water samples can be directly used for boron isotopic analysis without obvious sacrifice of precision, thus making this protocol more rapid than other ones.

•We study the matrix effects of calcium on sulfur isotope measurement by MC-ICP-MS.•The absolute concentration of matrix element affects the sulfur isotope ratios.•The absolute concentration of matrix element affects the 32S signal intensities.•We give suggestions about sulfur isotope analyses for gypsum and pore water.Multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been successfully applied in the rapid and high-precision measurement for sulfur isotope ratios in recent years. During the measurement, the presence of matrix elements would affect the instrumental mass bias for sulfur and these matrix-induced effects have aroused a lot of researchers’ interest. However, these studies have placed more weight on highlighting the necessity for their proposed correction protocols (e.g., chemical purification and matrix-matching) while less attention on the key property of the matrix element gives rise to the matrix effects. In this study, four groups of sulfate solutions, which have different concentrations of sulfur (0.05–0.60 mM) but a constant sequence of atomic calcium/sulfur ratios (0.1–50), are investigated under wet (solution) and dry (desolvation) plasma conditions to make a detailed evaluation on the matrix effects from calcium on sulfur isotope measurement. Based on a series of comparative analyses, we indicated that, the matrix effects of calcium on both measured sulfur isotope ratios and detected 32S signal intensities are dependent mainly on the absolute calcium concentration rather than its relative concentration ratio to sulfur (i.e., atomic calcium/sulfur ratio). Also, for the same group of samples, the matrix effects of calcium under dry plasma condition are much more significant than that of wet plasma. This research affords the opportunity to realize direct and relatively precise sulfur isotope measurement for evaporite gypsum, and further provides some suggestions with regard to sulfur isotope analytical protocols for sedimentary pore water.

Highlights•We investigate how concentration effect influences the measured δ34S values.•We construct a correction curve to correct measured δ34S values.•We apply the correction curve to AS solutions and pore water samples successfully.•Simultaneous measurement of sulfur concentrations is available.We have developed a technique for the rapid, precise and accurate determination of sulfur isotopes (δ34S) by MC–ICP–MS applicable to a range of sulfur-bearing solutions of different sulfur content. The 10 ppm Alfa-S solution (ammonium sulfate solution, working standard of the lab of the authors) was used to bracket other Alfa-S solutions of different concentrations and the measured δ34SV−CDTδ34SV−CDT values of Alfa-S solutions deviate from the reference value to varying degrees (concentration effect). The stability of concentration effect has been verified and a correction curve has been constructed based on Alfa-S solutions to correct measured δ34SV−CDTδ34SV−CDT values. The curve has been applied to AS solutions (dissolved ammonium sulfate from the lab of the authors) and pore water samples successfully, validating the reliability of our analytical method. This method also enables us to measure the sulfur concentration simultaneously when analyzing the sulfur isotope composition. There is a strong linear correlation (R2>0.999R2>0.999) between the sulfur concentrations and the intensity ratios of samples and the standard. We have constructed a regression curve based on Alfa-S solutions and this curve has been successfully used to determine sulfur concentrations of AS solutions and pore water samples. The analytical technique presented here enable rapid, precise and accurate S isotope measurement for a wide range of sulfur-bearing solutions – in particular for pore water samples with complex matrix and varying sulfur concentrations. Also, simultaneous measurement of sulfur concentrations is available.Graphical abstract