Direct analysis of nanoparticles in organic solvents by ICPMS with microdroplet injection

Abstract

In recent years, the capabilities for characterizing inorganic nanoparticles (NPs) in aqueous solvents with respect to their elemental composition, mass and particle number concentration have been expanded using single particle inductively coupled plasma mass spectrometry (sp-ICPMS). However, NPs with high monodispersity, size, shape and surface chemistry control are frequently synthesized using hot-injection methods, utilizing hydrophobic organic ligands which are only soluble in non-polar organic solvents. Due to several instrumental limitations, suspensions in organic solvents are not commonly analysed by sp-ICPMS. In this study, we investigated the direct introduction of toluene and mesitylene into an ICPMS using a microdroplet generator. With this configuration the solvent load in the ICP is substantially reduced and soot formation, causing instrumental drift, was minimized while maintaining a transport efficiency (TE) of 100%. Furthermore, the effect of different vacuum interface configurations and the addition of oxygen or nitrogen on the detection efficiency (DE) and instrumental background signals was investigated for Al, Si, Ti, Fe Cu, Ag, Cd, and Pb. The highest DE was obtained for a “Jet” interface with the addition of nitrogen at a flow rate of 10 mL min⁻¹, resulting in an increase by a factor of 2–8 depending on the element. The lowest detectable mass, based on counting statistics, was 1.4 ag for Pb, which corresponds to a diameter of 6.1 nm of a spherical, metallic NP. The approach can not only be used for NP characterization, but also holds promise for the sensitive determination of trace elements in organic solvents.