Accurate high-resolution LA-ICP-MS determination of trace element contents in carbonates with matrix-matched standards

Abstract

As one of the primary climate archives on earth, carbonates in different geological settings (e.g. corals, foraminifera, mollusks, and speleothems) can record multiple facets of the climate system with their elemental and isotopic compositions. In situ geochemical measurements of carbonates at high spatial resolution have the potential to generate climate records at annual, seasonal or even higher temporal resolution, yet such measurements are often costly and associated with relatively high analytical uncertainties. The accuracy of in situ measurements of trace element contents in carbonates can be additionally complicated by the availability of homogeneous and matrix-matched calibration standards. Here we propose a calibration method based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for trace element contents in natural carbonate samples, measured in element-to-calcium (El/Ca) ratios, with a series of commercially available nanoparticulate carbonate standards of various origins and compositions. Through a series of tests, we demonstrate that these nanoparticulate carbonate standards have sufficient homogeneity to serve as matrix-matched reference materials. With El/Ca calibration lines obtained from the standards, our method is able to generate more accurate and reproducible measurements of a dozen El/Ca ratios in carbonates at 15 μm or better resolution. Accurate high-resolution characterization of trace element contents in carbonates can not only improve our understanding of the evolution of earth's environmental history, but also shed light on the formation mechanisms of carbonate minerals of different origins.