Organics non-spectral interferences on nanoparticle characterization by means of single particle inductively coupled plasma mass spectrometry

Abstract

The number of studies devoted to nanomaterial characterization in organic matrices by means of spICP-MS grows every year, but limited information is available about the non-spectral interferences generated by this type of matrix. A better understanding of this interference is a prerequisite for developing more robust methodologies and improving spICP-MS accuracy. The goal of this work is to investigate non-spectral interferences due to organics on nanoparticle (NP) characterization (i.e., number concentration and size distribution) by means of spICP-MS. To this end, the influence of the NP composition and size (i.e., Au-, Pt- and SeNPs), the carbon source (i.e., 6% w/w glycerol and 10% w/w ethanol), ICP-MS operating conditions (i.e., sampling depth and nebulizer gas flow) and instrument design on matrix effects have been evaluated. It was observed that 10% w/w ethanol gives rise to positive matrix effects on the number concentration due to changes in aerosol generation and transport with regard to water standards. Irrespective of the organic source employed, either positive or negative bias on the size distributions can be obtained and these effects depend on plasma operating conditions, instrument characteristics and NP composition. In addition to changes in transport efficiency, matrix effects on size distribution also depend on plasma characteristics and carbon-based charge transfer reactions (Au and Se). Organics non-spectral interferences can be mitigated by means of internal standardization. When operating with 10% w/w ethanol, two internal standards (ionic solution plus a NP suspension of known concentration) are simultaneously required for correcting changes in analyte ionization and transport. For 6% w/w glycerol, however, just a single internal standard (ionic solution) is necessary since this matrix does not affect aerosol generation and analyte transport. A novel measurement procedure is proposed for measuring the internal standards and the NPs of interest without compromising the sample throughput.