Contribution to Accurate Spherical Gold Nanoparticle Size Determination by Single-Particle Inductively Coupled Mass Spectrometry: A Comparison with Small-Angle X-ray Scattering.

Small-angle X-ray scattering spectroscopy (SAXS) is the method of choice for nanoparticle diameter and concentration determination. On the one hand, it is metrologically traceable for spherical nanoparticle mean diameter determination and does not require any sample preparation or calibration. On the other hand, single-particle inductively coupled mass spectrometry (SPICPMS) is still under development and requires involved process clarification and accuracy improvement. The strategy of this study is the comparison of the two techniques to study comprehensively SPICPMS performance and observe phenomena otherwise hidden. Six spherical gold nanoparticle suspensions distributed over a large size range (30, 50, 60, 80,100, and 150 nm) are studied as calibration points. Potential matrix effects are eliminated by stabilizing nanoparticles with chitosan in HCl. Chitosan encapsulates nanoparticles, stabilizes their dispersion, and protects them from dissolution. Detection counting/analogue threshold and timeout appear as the relevant parameters for transient signals. They show an influence not only on mean signal but also on signal distribution. The detection tuning proposed allows to linearly calibrate the nanoparticle distribution signal to cubed diameter over the entire range studied with no sensitivity diminution. Comparing the three classical transport efficiency methods, size transport efficiency is shown as the most accurate. The new procedure is validated analyzing three gold nanoparticle suspensions (135, 40, and 50 nm). The results are consistent with SAXS measurements.