Line-dropped gelatin multi-element calibration standards in LA-ICP-MS: a statistically verifying comparison with cryosectioned homogenized lung and liver as matrix-matched calibration standards and as corresponding reference materials

Calibrations in LA-ICP-MS are typically very time-consuming and complex, as they need to be matched to the samples being measured and sectioned on a microtome. Alternatively, gelatin can be in droplet form or as a section, which is a more recent development. In this study, we report on investigations where hot multi-element gelatin solutions are placed in a linear fashion on microscopic slides to conduct comparative statistical observations between doped tissue homogenates from the liver and lung. The tissue homogenates served as both samples (complete ablation) and calibration standards (partial ablation) for verification purposes. We explored the effects of different laser fluences (0.50-1.50 J/cm²), gelatin contents (0.3-20.0%) and section thicknesses (10-30 µm). To do this, we evaluated the samples by calculating median and mean values over the entire section with and without removal of elementary spikes (de-spiking). A reduction in distribution was achieved with averaging. The data was normalized using ¹³C as an internal standard. In these experiments and under these measurement conditions, it was observed that the selected laser fluences, gelatin contents, and section thicknesses did not visibly affect the results, making them comparable. Each sample could be assessed with each gelatin calibration, allowing for determination of expected reference values. Despite interruptions in the measurement operation, due to the high number of measurements, where samples and calibrations could not be analyzed in one measurement run, no negative effects of stopping and starting the LA-ICP-MS were observed.