Trace element analysis of whole-rock glass beads of geological reference materials by Nd:YAG UV 213 nm LA-ICP-MS

Abstract

A trace element composition of rock samples is difficult to determine when they contain refractory minerals that are hardly dissolved with conventional acid digestion techniques. Fused glass beads of rock samples could be an adequate target to circumvent this problem. We here report inductively coupled plasma-mass spectrometry (ICP-MS) results for geological reference materials (GRMs) prepared to normal- (sample/flux = 1:5) and low-dilution (sample/flux = 1:2) glass beads by using Nd:YAG UV 213-nm laser ablation system. Concentrations of 24 trace elements (Ba, Hf, Nb, Rb, Sr, Ta, Th, U, Y, Zr, and 14 rare earth elements (REEs)) were analyzed for three USGS GRMs (G-3 granite, AGV-2 andesite, and BHVO-2 basalt). Each analysis for the GRM beads was performed as spot (ca. 55 μm diameter) analysis with 120-s ablation time. The depth-to-diameter ratio of the laser spot was low (<4) enough to prevent significant elemental fractionation. The NIST612 glass and 29Si were employed as the external standard and the internal standard element, respectively. When the middle half of time-integrated data was taken to minimize the fractionation effect, the low-dilution fused glasses yielded reproducible and accurate results for all analyzed elements. In the case of normal-dilution fused glasses, comparable precision and accuracy were obtained only for elements with concentrations higher than 1 μg g−1, likely resulting from higher dilution ratios. Low-dilution glass beads can be an adequate target to analyze trace element composition of rock samples by using the laser ablation ICP-MS. This simple and rapid technique can be applied directly to the same glass beads prepared for major elemental analysis using the XRF.