Validation of LA-ICP-MS trace element analysis of geological glasses using a new solid-state 193 nm Nd:YAG laser and matrix-matched calibration

Abstract

We have investigated the performance of a combined single-collector sector-field ICP-MS and a new solid-state 193 nm Nd:YAG laser ablation system for trace element analysis of geological glasses. Experiments were made with certified MPI-DING, USGS and NIST reference glasses. Two different measurement protocols were used: the conventional three-spot analysis (spot sizes: 50–100 μm) for the determination of 26 trace elements using a combination of magnetic (Bscan) and electrical scan (Escan) modes and the major element Ca as internal standard (protocol 1), and a high-precision technique for the determination of three elements using the fast Escan at a constant magnetic field and a trace element as internal standard (protocol 2). We obtained a precision (1 RSD) of element ratio measurements of about 0.8% (protocol 1) and 0.2% (protocol 2), which is better than that obtained using a 213 nm Nd:YAG laser (about 1.1% and 0.6%, respectively). The mean reproducibility (1 RSD) of trace element data obtained over a period of three months was about 2% (100 μm spot size) and 3% (50 μm spot size). The detection efficiencies of the mass spectrometer for elements with Z = 37 (Rb)–92 (U) range between 0.2 × 10⁻³ and 2 × 10⁻³ detected ions/ablated atoms. They are about 40% higher than those using a 213 nm laser because of lower sample consumption of the 193 nm laser ablation system (ca. 0.05 μm ablation per shot). Detection limits decrease with increasing atomic number; they range between 0.1 μg g⁻¹ (Rb) and 0.0003 μg g⁻¹ (U). We also investigated element fractionation and possible matrix effects, which may bias the analytical results. Element fractionation for the 193 nm laser is lower than for the 213 nm laser. Low (percent range), but significantly different fractionation factors of some elements (e.g., Rb, Y, Pb) for glasses having different major element compositions are observed. Highly accurate LA-ICP-MS analyses therefore require suitable reference materials of similar matrices. The eight MPI-DING glasses having different major element compositions seem to be such samples for geoanalytical work. The basaltic KL2-G glass and the komatiitic GOR132-G glass were used for calibration of six basaltic and one komatiitic reference glasses, respectively. Most LA-ICP-MS data agree with published compilation values and isotope dilution data within 95% confidence limits.