High spatial resolution trace element determination of geological samples by laser ablation quadrupole plasma mass spectrometry: implications for glass analysis in volcanic products

Abstract

Increasing the spatial resolution of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a challenge in microanalysis of geological samples. Smaller sizes for the laser beam will allow for (1) high resolution determination of trace element compositions, (2) accurate estimation of crystal/melt partition coefficients, (3) detailed characterization of diffusion profiles, and (4) analysis of fine volcanic glasses. Here, we report about the figures of merit for LA-ICP Quadrupole MS down to a spatial resolution of 5 {\mu}m. This study highlights the possibility to achieve suitable limits of detection, accuracy and precision for geological samples even at spatial resolutions of the order of 5 {\mu}m. At a beam size of 15 {\mu}m precision (measured as one sigma) and accuracy (expressed as relative deviation from the reference value) are of the order of 10%. At a smaller beam size of 8um, precision decreases to 15% for concentration above 1.7 {\mu}g g-1. As the beam size is decreased to ~5 {\mu}m, precision declines to about 15% and 20% for concentrations above 10 {\mu}g g-1 using 42Ca and 29Si as internal standard, respectively. Accuracy is better or equal to 10% and 13 % at beam sizes of 15 and 10 {\mu}m respectively. When the spatial resolution is increased to 8 {\mu}m, accuracy remains better than 15% and 20% for 42Ca and 29Si as internal standard, respectively. We employed such high-resolution techniques to volcanic glasses in ash particles of the 2010 Eyjafjallaj\"okull eruption. Our results are well consistent with the previously reported data obtained at lower spatial resolution, supporting the reliability of the method.