In situ trace element determination of carbonates by laserProbe inductively coupled plasma mass spectrometry using nonmatrix matched standardization

Abstract

Abstract The LaserProbe Inductively Coupled Plasma Mass Spectrometry (LP-ICP-MS) has shown great potential to precisely and quickly determine trace element compositions of minerals in situ at a scale of ≤ 60 μm. However, standardization is complicated, due to the lack of matrix-matched, homogeneous mineral standards. In this study, a nonmatrix matched calibration standard, the NIST 612 silicate glass, was employed to determine Sr, Y, Ba and REE concentrations in calcite and dolomite grain mounts. Using 43Ca as an internal standard, the results demonstrate that it is not essential to have a matrix-matched mineral standard by LP-ICP-MS. Routine limits of detection are ~10 ppb for REEs and ~200 ppb for Sr, Y and Ba, depending on laser operating conditions. Evaluation of precision and accuracy is made complex by heterogeneity of trace elements within single mineral grains. However, the best within-grain precision (determined from several LP sampling pits within an individual mineral grain) is considered to represent the maximum analytical error and is generally 10 grains) were analyzed. Nonmatrix matched standardization for quantitative analysis can successfully be used, because the small size laser probe ( ~ 10 μm) used in this study can generate much higher power density than the conventional size laser beam. At high power density, the sample ablation mainly results from plasma plume expansion induced by the laser, not from absorption of the laser beam and related thermal vaporization, as for conventional, low power density laser analysis. The plasma plume expansion as a major ablation process permits the ablation of even those materials usually transparent to laser (e.g., calcite). This technique can be applied to the analysis of trace elements of carbonates in thin sections, grain mounts and rock or mineral chips, thus avoiding extensive sample preparation with significant implications for studies of near-surface and environmental processes.