Dual-standard matrix-matched calibration strategy for LA-ICP-MS elemental quantitative imaging of calcium oxalate-uric acid dual-matrix urinary stones

Abstract

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a powerful technique for spatially resolved elemental imaging; however, its analytical accuracy is often limited by matrix effects, especially in heterogeneous, multi‑matrix samples. The analysis of urinary stones, which frequently consist of mixed matrices such as calcium oxalate (CaOx) and uric acid (UA), presents significant challenges in matching the sample matrix with an appropriate matrix‑matched external standard, especially when processing the tens of thousands of LA-ICP‑MS data points typically required for elemental mapping. This study presents a novel strategy that utilizes calcium (Ca) as a matrix tracer to distinguish between CaOx and UA components in complex urinary stones. Twelve consecutive quadrupole readouts of each scan were grouped, and a t-test was applied to assess whether the 13th data point differed significantly from the preceding 12, based on the 44Ca signal intensity. This process was repeated in a moving-window fashion (e.g., from the 2nd to 13th point, then 3rd to 14th, etc.) along the entire scan. By leveraging Ca signal profiles in conjunction with statistical t-tests, the proposed method effectively identifies matrix boundaries. Subsequently, a dual‑standard calibration strategy was developed using in‑house CaOx‑1 and UA‑6 reference pellets, enabling accurate and reproducible elemental quantification. This approach significantly reduces analytical errors, such as –84 % for Mg and up to 183 % for Zn, that arise from the inappropriate selection of external or internal standards. The resulting elemental distribution images uncovered distinct compositional layering, which significantly improves the analytical performance of LA-ICP-MS in studying complex urinary stone compositions and holds promise for advancing research on their pathogenesis and treatment.