Optimization of instrumental parameters for improving sensitivity of single particle inductively-coupled plasma mass spectrometry analysis of gold

Single particle inductively-coupled plasma mass spectrometry (spICP-MS) is a promising technique for analysis of engineered nanoparticles, whose utilization has increased substantially over the past years. Optimization of instrumental conditions is, however, crucial to improve the sensitivity and precision of nanoparticle (NP) detection. In this study, the influence of ICP-MS instrumental parameters (nebulizer gas flow, plasma radiofrequency-power and sampling depth) on the signal intensity of gold in spICP-MS was evaluated using dispersions of Au NPs and a solution of dissolved gold. The interaction effects of the main factors were found to have a significant effect on the signal intensity, proving that factor values should be jointly optimized instead of one at a time, if maximum ion signal is expected. Optimization of instrumental parameter values was performed for both analyte forms and found to be in a good agreement, indicating a similar behavior of the particles in plasma compared with the dissolved analyte. However, some differences in the behavior of the two analyte forms as regard to sampling depth position was observed. Particle size or the presence of complex sample matrix was not found to influence the optimal instrumental parameter values, however, a significant signal depression for gold was observed (up to 50%) in matrices containing high levels of sodium. Compared to frequently used ‘robust conditions’, a 70% increase in the ion signal intensity of gold and a 15% decrease in the particle size detection limit was achieved with instrumental parameter optimization. As such, instrumental parameter optimization for sensitive NP analysis can be seen as highly beneficial procedure.