Determination of size and particle number concentration of metallic nanoparticles using isotope dilution analysis combined with single particle ICP-MS to minimise matrix effects

Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is a powerful tool for metallic nanoparticle (NP) characterisation in terms of concentration and, taking into account several assumptions, also size. However, this technique faces challenges, such as the intrinsic matrix effect, which significantly impact the results when analysing real complex samples. This issue is critical for the calculations of key SP-ICP-MS parameters ultimately altering the final outcomes. Novel analytical approaches with high metrological quality such as isotope dilution analysis (IDA) can overcome these limitations by improving signal discrimination in challenging SP-ICP-MS scenarios. This alternative has mainly been applied for NP size characterisation but remains underexplored in modern ICP-MS and SP set-ups. Thus, the implementation of a revised version of IDA-SP-ICP-MS, including recent advances in quadrupole ICP-MS and SP data processing, which enables reliable NP sizing and counting, would be of utmost interest. In this work, this combination using the species-unspecific IDA mode has been investigated as an alternative to tackle matrix effect caused by complex matrices with platinum NPs as a case study. The optimum ionic tracer concentration has been evaluated for different PtNP sizes, resulting in a range of 500 to 1000 ng L⁻¹ due to differences in the mean NP signal. A valuable in-house spreadsheet for the data treatment has also been developed. The successful applicability of the methodology for determining the size and particle number concentration of 30 and 50 nm PtNPs has been demonstrated not only in environmental samples (synthetic and natural seawater), but also, for the first time, in biological matrices such as cell culture media and human urine.

Graphical Abstract