LA-ICP-TOF-MS for quantitative mapping of biogenic carbonate samples using matrix-matched nanoparticulate pressed powder pellets

Abstract

This study evaluated the micro-homogeneity of seven different commercially available nanoparticulate pressed pellets based on a CaCO₃ matrix and their utility for quantitative elemental mapping of biogenic carbonates using laser ablation-inductively coupled plasma-time-of-flight-mass spectrometry (LA-ICP-TOF-MS). The analytical performance of matrix-matched calibration (using the aforementioned nano-pellets) was compared against that of non-matrix-matched calibration using a silicate glass (NIST SRM 610) reference material for quantification. Calibration with nano-pellets, combined with the use of Ca as an internal standard, significantly improved the quantification accuracy, providing recoveries between 80–120% for the majority of the 18 elements selected and spread across a wide concentration range (from sub-μg g⁻¹ to tens of wt%). However, some nano-pellets (e.g., BPLM-NP and BAM-RS3-NP) exhibited higher heterogeneity, leading to biased recoveries. Also, an inverse correlation between the mass fraction and the relative standard deviation (RSD) was observed. Throughout the work, elemental mapping was conducted with a laser beam size of 20 × 20 μm² as a compromise between spatial resolution, sensitivity (sub-μg g⁻¹ limits of detection required for trace elements), linear dynamic range, total analysis time and size of the region-of-interest. The quantitative mapping approach enabled the generation of high-resolution, multi-elemental 2D-maps of various CaCO₃-based natural chronological archives, including fish otoliths and bivalve shells, revealing detailed elemental distribution patterns for both trace (e.g., Mn, Ba) and major elements (e.g., Sr). This LA-ICP-TOF-MS methodology provides a powerful tool for resolving intricate microstructures and thus, for chronologically tracking bioaccumulation of environmentally relevant metals, offering significant advantages over traditional 1D (line scanning) analysis as the latter may lead to misinterpretation of elemental distributions.