Time resolved trace element calibration strategies for LA-ICP-MS

There are many processes that affect the measured concentration of elements determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Depending on the element of interest, a range of corrections are required to account for sensitivity drift and downhole effects, as well as other sources of inaccuracy. Here, we present a new method of calibrating LA-ICP-MS measurements taking into consideration time-dependent sensitivity changes to produce a three-dimensional calibration surface through time. These 3D calibration surfaces result in up to 20% improvements in our example dataset for some elements. To ensure calibration surfaces that are created using multiple reference materials are not degraded by matrix effects a median yield correction factor is determined relative to a primary reference material. We also introduce sensitivity modelling for elements without accepted values or where interferences may affect calibration. In addition to the correction of drift, we further demonstrate a correction for downhole fractionation effects can improve the precision of spot analyses by up to 20% in our example dataset. A flexible solution to the sum normalisation approach is briefly introduced for calibration of multi-phase samples using different calibration parameters, along with a residual correction based on compositional affinity to a reference material. Combined, these new methodologies can improve the accuracy and precision of concentration determinations by LA-ICP-MS in a wide variety of applications.