Use of Non‐Matrix Matched Reference Materials for the Accurate Analysis of Calcium Carbonate by LA‐ICP‐MS

Abstract

Advances in laser ablation inductively coupled plasma‐mass spectrometry have improved analytical precision for mineral analysis, expanding geological interpretations from LA‐ICP‐MS results. However, with improvements in analytical precision, systematic errors from calibration can become more obvious and affect data quality. To improve the accuracy of the LA‐ICP‐MS technique, a fully quantified method is presented for the analysis of minerals with a CaCO3 matrix. An in‐house calcite sample (P‐Cal) was developed with an independently constrained composition and compared with measurement results from LA‐ICP‐MS analysis, generated using multiple spot sizes, laser fluences and calibration methods. For many elements, calibration against NIST SRM 612 as a calibration reference material and USGS GSD‐1G and USGS BCR‐2G as secondary reference materials (calibration B) provided the best accuracy for CaCO3 analysis. Ablation rates and element yield (ICP‐MS signal intensity in counts per second for a given isotope relative to the mass fraction of the respective element) in calcium carbonate closely resembles NIST SRM 612; however, the down‐hole fractionation curves of USGS BCR‐2G (basaltic glass matrix) are a better fit for carbonate. Variations in accuracy for measurements at different spot sizes are negligible compared with the other effects discussed. Additionally, ablation characteristics for powdered crystals versus large fragments produce a negligible effect on the accuracy of the results for calcium carbonate.