Validation of Single Particle ICP-MS for Routine Measurements of Nanoparticle Size and Number Size Distribution
Antonio R. Montoro Bustos, Premsagar P. Kavuri, Antonio M. Possolo, Natalia Farkas, Andras Vladar, Karen E. Murphy, Michael R. Winchester
Single particle inductively coupled plasma-mass spectrometry (spICP-MS) is an emerging technique capable of measuring nanoparticle size and number concentration simultaneously, of metal-containing nanoparticles (NPs) at environmentally relevant levels. spICP-MS will become an established measurement method once the metrological quality of the measure-ment results it produces will have been proven incontrovertibly. This paper presents for the first time a rigorous validation of spICP-MS capabilities for measuring mean NP size and number size distribution of gold nanoparticles (AuNPs). The valida-tion is achieved by: (i) calibration based on the consensus value for particle size derived from six different sizing techniques applied to National Institute of Standards and Technology (NIST) Reference Material (RM) 8013; (ii) comparison with high-resolution scanning electron microscopy (HR-SEM) used as a reference method, which is linked to the SI through a calibra-tion standard characterized by the NIST metrological Atomic Force Microscope; and (iii) evaluating the uncertainty associ-ated with the measurement of the mean particle size to enable comparison of the spICP-MS and HR-SEM methods. After establishing HR-SEM and spICP-MS measurement protocols, both methods were used to characterize commercial AuNP suspensions of three different sizes (30 nm, 60 nm, and 100 nm) with four different coatings and surface charge at pH 7. spICP-MS measurements (corroborated by HR-SEM analyses) revealed the existence of two distinct sub-populations of particles in the number size distributions for four of the 60 nm commercial suspensions, a fact that was not apparent in the measurement results obtained by transmission electron microscopy (TEM) supplied by the vendor. This finding illustrates the utility of spICP-MS for routine characterization of commercial NP suspensions regardless of size or coating.