Combined use of multiple external and internal standards in LA-ICP-MS analysis of bulk geological samples using lithium borate fused glass

Abstract

We describe a method for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) elemental analysis of geological materials using low-dilution Li-borate fused glass wavelength dispersive X-ray fluorescence (WDXRF) pellets, with samples, drift monitor and 18 reference materials (RMs) identically prepared. After analysis for 46 elements by WDXRF, LA-ICP-MS intensities from samples and RMs are collected, and background corrected with Iolite software. HALite, a new software application, was developed to derive the elemental compositions from the LA-ICP-MS net signals. In HALite, elements are drift-corrected using polynomial functions, and flux-fused RM element sensitivities are calculated from known mass fractions. Multiple internal standard (IS) elements are used to model each sample’s laser response. Analyte mass fractions in unknowns are determined using the calibrated sensitivity correlation models for multiple IS elements. Either the WDXRF mass fractions or the initial round of calculated LA-ICP-MS mass fractions are used to calculate weighted mean sensitivities. Validation experiments with flux-fused RMs run as unknowns yield results with less than 5–10% total relative uncertainty for most analytes. We derive equations which allow calculation of the precision and total uncertainty as a function of mass fraction for each analyte element.