Detection of nanoparticles by single-particle ICP-MS with complete transport efficiency through direct nebulization at few-microlitres-per-minute uptake rates

Abstract

Measurement of nanoparticle (NP) concentration and size by single-particle inductively coupled plasma mass spectrometry (spICP-MS) usually requires the use of a NP reference material to determine the loss of NPs and/or ions during their transport from the sample solution to the detection system. The determination of this loss, qualified as nebulization efficiency (η_Nebulization) and/or transport efficiency (η_Transport), is time-consuming, costly and lacks reliability. Nebulization of the NPs directly into the plasma (without a spray chamber) results in η_Nebulization = 100% and is thus a promising strategy to avoid these calibration steps. In this work, we used the μ-dDIHEN introduction system: a demountable direct injection high-efficiency nebulizer (dDIHEN) hyphenated to a flow-injection valve and a gas displacement pump. For the first time with a continuous flow nebulizer, complete transport efficiency was reached (i.e. η_Transport = 100%). Operated at a very low uptake rate (as low as 8 μL min⁻¹), the μ-dDIHEN accurately and reproducibly determined average diameters of Au-, Ag- and Pt-NPs, in full agreement with their reference values. It was also successfully tested for Au-NPs in complex matrices, such as surface waters. spICP-MS analyses with the μ-dDIHEN sample introduction system only require a dissolved standard calibration to determine NP average diameter (d_NPs in nm) and number concentration (N_NPs) from the simplified set of equations: \( \overline{d_{NPs}}=\sqrt[3]{\frac{6.\kern0.5em \left(\overline{I_{NPs}}-{I}_{bckgd}\right).\kern0.5em {t}_d.{q}_{liq}}{S.\kern0.5em {f}_a.\kern0.5em \pi .\kern0.5em \rho }} \) and \( \overline{N_{NPs}}=\frac{\overline{D_{NPs}}}{q_{liq}.\kern0.5em D.\kern0.5em {t}_{d.}} \) Graphical abstract