Potential clinopyroxene and orthopyroxene reference materials for SIMS water content analysis

Abstract

Secondary ion mass spectrometry (SIMS) is a powerful technique for in situ measurement of trace amounts of water in nominally anhydrous minerals (NAMs). The structure and chemistry of the substrate are well known to have a significant effect on how easily elements are ionized when sputtered with a primary beam, resulting in different ion yields, i.e., matrix effect. The matrix effect highlights the importance in choosing reference materials with a similar crystal structure and chemistry for calibration. However, these kinds of reference materials are generally scarce. In this study, we investigate four clinopyroxene (cpx) and five orthopyroxene (opx) newly developed reference materials for SIMS water content analysis. Nine samples were analyzed via a Fourier Transform Infrared Spectrometer (FTIR) and SIMS to determine their water content and investigate their homogeneity. Our results show that these samples are homogeneous in terms of water contents, indicated by the low standard deviation (<18.6%, 2sd) for both inter- and intra-fragments, except that Diopside-cpx shows some inter-fragment heterogeneity, which should be used with caution. The cpx and opx sample suites have water ranges of 24 ± 3 to 774 ± 26 μg g⁻¹ (2sd) and 45 ± 3 to 534 ± 59 μg g⁻¹ (2sd), respectively, extending the covered ranges of the existing reference materials and approaching most natural samples. Thus, these samples can be used as reference materials for SIMS pyroxene water content analysis.