Introducing a modified sample preparation and straightforward elemental ratio determination strategy with LA-ICP-MS to expand the nanoparticle probing toolkit

Abstract

Nanoparticles (NPs) are employed in a wide range of applications due to some of their unique characteristics. Since their properties are partly determined by their composition, accurate determination of their stoichiometry is of paramount importance for optimization and fine tuning of their properties. We propose a laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) procedure which enables determination of NP composition. Small NP quantities (approx. 1 mg) are dispersed in a polymeric solution which is then spin coated onto a Si wafer, thereby ensuring uniform distribution of the NPs within the thin polymer film deposited on the Si substrate. Matrix-matched standards are similarly prepared by mixing elemental aqueous stock solutions with the same polymer solution, followed by spin coating. After thorough optimization of the sample preparation, and the parameters used for laser-ablation and subsequent ICP-MS analysis, the content of the analytes could be determined with a relative standard deviation (RSD) of < 2 % for standards and < 3–8 % for the NP samples, depending on the NP type, with detection limits lower than 0.2000 µg/g for all elements. Based on the results determined for the individual NP constituents, prevailing elemental ratios have been assessed. Yttria-doped zirconia of known stoichiometry, i.e., (ZrO₂)0.98(Y₂O₃)₀.₀₈, was used as a reference material to validate the fit of the developed approach for the stoichiometric determination of NPs. The experimentally determined stoichiometry is in agreement with the one provided by the manufacturer. The applicability of the method is further demonstrated by assessment of the loading of CdS rods with medium-entropy (CoNiMoW)S NPs, which are interesting as novel catalysts and stoichiometric determination of Zr-based metal organic frameworks (MOFs), which function as catalysts in CO₂ reduction.