Assessing rare earth elements in stalagmites at parts-per-billion levels using LA-ICPMS

Abstract

Here we propose a highly-sensitive quantitative approach to determine ultra-trace rare earth elements (REEs) profiles in intact stalagmite samples, allowing the identification and localization of anomalies caused for example by volcanic eruptions. The approach combines a highly sensitive sector field ICPMS with a laser sampling approach in open atmosphere followed by gas exchange for sample introduction. The use of a “jet” vacuum interface and the addition of small amounts of N2 gas allowed for a 20-40 fold sensitivity enhancement compared to the conventional interface configuration. Mass load effects, quantification capabilities and detection power were investigated in analyses of reference materials using various combinations of spot sizes and laser repetition rates. From 160 µm diameter circular laser spots and 10 Hz ablation frequency, limits of detection were in the low or sub-ng g-1 range for REEs. Relative deviations of quantified concentrations from USGS MACS-3 preferred values were smaller than 12%. The analytical approach enabled the determination of REE concentration profiles at the single digit ng g-1 level. This well-characterized open-cell LA-ICPMS methodology gives the potential to apply to other natural carbonates, such as travertine, tufa, and flowstones, for providing a better comprehension of earth and environmental sciences.