A 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 application in urinary stones, which often comprise 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 tens of thousands of LA-ICP-MS data points typically required for elemental imaging. 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 identify matrix boundaries. This method enables the precise identification of boundaries on the scale of tens of micrometers that are indistinguishable to the naked eye in micrographs. Two matrices were thus identified, and 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 arising from inappropriate selection of external or internal standards, previously estimated as −84% for Mg and up to 183% for Zn. 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.