Silver nanoparticle characterization using single particle ICP-MS (SP-ICP-MS) and asymmetrical flow field flow fractionation ICP-MS (AF4-ICP-MS)

Methods to detect, quantify, and characterize engineered nanoparticles (ENPs) in environmental matrices are highlighted as one of the areas of highest priority research needs with respect to understanding the potential environmental risks associated with nanomaterials. More specifically, techniques are needed to determine the size and concentration of ENPs in a variety of complex matrices. Furthermore, data should be collected at environmentally and toxicologically relevant concentrations. Both single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) and asymmetrical flow field flow fractionation (AF4) ICP-MS offer substantial advantages for detecting ENPs and assessing many of the above parameters in complex matrices over traditional characterization methods such as microscopy, light scattering, and filtration. In this study, we compared the ability of two emerging techniques to detect well characterized, monodisperse silver ENPs and examined their overall applicability to environmental studies specifically with respect to their: (A) size and concentration detection limits, (B) resolution and (C) multi-form elemental analysis. We find that in terms of concentration detection limit (both, on a mass basis and particle number basis) SP-ICP-MS was considerably more sensitive than AF4-ICP-MS (ng L-1 vs. mu g L-1, respectively), and offers the unique ability to differentiate dissolved and nanoparticulate fractions of total metal. With a variety of optimization parameters possible, AF4-ICP-MS can detect a much smaller NP size (2 nm vs. 20 nm for SP-ICP-MS), provides the possibility for greater size resolution.