In Situ Accurate Analysis Of Trace Elements Of Carbonate By LA-ICP-MS

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) provides a powerful technique for analyzing small samples. The advantages of minimal sample preparation, low blanks, high spatial resolution (generally>10μm) and rapid throughout (generally<3 min per point) make LA-ICP-MS a cost-effective and attractive analytical tool for microanalysis of not only natural silicate minerals, but also carbonatite melt inclusion and biological materials with incremental growth structures (e.g., coral, shell and otolith). The overwhelming majority of LA-ICP-MS analyses published in the literature are calibrated using NIST SRM 600 series glasses conjunction with internal standardization. Concentration of the internal standard (e.g., Ca) is determined either by an independent method (e.g. electron microprobe) or according to the constant stoichiometry of the mineral. Here we describe an internal standard-independent calibration strategy for LA-ICP-MS analysis of fifty-four major and trace elements in carbonate. Based on the normalization strategy of bulk components as 100%, the MRM-NoIS (calibrated against multiple silicate reference materials without using internal standard) was used to correct the matrix-dependent absolute amount of materials ablated during each run. Applying MRM-NoIS and using the MPI-DING reference glasses as reference materials for external calibration, analyses of carbonate standard MACS-3 generally agree with recommended values within 10% for most trace elements (better than 5% for REEs and major elements). Analyses of natural igneous calcite grains agree with the results of solution-ICP-MS values within 10% for Mg, Sc, Mn, Sr and REEs. The results indicate that, applying MRM-NoIS and using MPI-DING reference glasses as multiple reference materials for calibration, carbonate can be accurately analyzed in situ by LA-ICP-MS without applying internal standardization and matrix matching external standards. Our results also indicate that the working value of Nb in carbonate pellet MACS-3 could be 53.4μg/g rather than 35.2μg/g given in the test of G-Probe 4.