New developments in the analysis of composite nanoparticles using single particle ICP-MS and field-flow fractionation

Release of engineered nanomaterials (ENMs) into the environment is inevitable as the nanotechnology industry continues to expand producing a multitude of nanotechnology-enabled products (NEPs). In this work, advancements in single particle inductively coupled plasma mass spectrometry (spICP-MS), used in tandem with the particle separation capabilities of field-flow fractionation (FFF), were made in order to quantitatively address two challenges: 1) the detection, characterization, and quantification of a composite particle representing the formation of a surface coating upon release of inorganic engineered nanoparticles (ENPs), and 2) the need to distinguish ENPs from interfering natural nanoparticles (NNPs).;An inorganic-core/organic-shell composite particle was characterized using spICP-MS and two FFF techniques. A model Au-PS-b-PAA nanoparticle (NP) consisting of 50 nm Au NPs incorporated into polystyrene micelles was used to represent a) the formation of surface coatings on inorganic NPs and b) polymer fragments released from inorganic ENP-containing polymer nanocomposites due to material weathering or abrasion. spICP-MS analysis of the composite particle indicated that multiple Au NPs were incorporated into the PS-b-PAA micelles, consistent with transmission electron microscopy (TEM) results. The presence of multiple NPs resulted in an average incorporated Au equivalent size of 63 nm. Particle separation by asymmetric flow field-flow fractionation (AF4) provided a distribution of the composite particle hydrodynamic size (about 70-400 nm). Analysis of the fractions by spICP-MS provided the incorporated Au mass, which demonstrated that as the Au-PS-b-PAA NP hydrodynamic size increased, the number of incorporated Au NPs (i.e., Au mass) increased. Additionally, separation by an additional FFF technique, centrifugal FFF, and analysis of the fractions by spICP-MS provided the Au NP mass distributions in the Au-PS-b-PAA NPs as the mass of incorporated NPs increased.;One of the challenges of detecting ENPs in the environment is distinguishing them from NNPs. ENPs have elementally pure compositions while NNPs contain multiple elements. A bimetallic core-shell NP (Au-core/Ag-shell) was used as model for NNPs in order to develop nano-metrology techniques suitable for the detection of interfering NNPs. The Au-core/Ag-shell NP was first used to demonstrate how current spICP-MS capabilities (i.e., using single element analysis) in combination with AF4 can be utilized not only to determine the bimetallic composite nature of the Au-Ag core-shell NP but can also be used to reveal the core-shell structure by temporally observing a slow acid digestion of the particles. Particle number concentrations provided by spICP-MS and AF4-ICP-MS analysis showed that the particle solution contained composite NPs rather than individual Au-only and Ag-only NPs. spICP-MS was then used to observe particle dissolution in dilute acid over time to reveal the core-shell particle structure. A recent development in spICP-MS technology, dual element analysis with a quadrupole mass analyzer, offers the ability to quickly determine the composition of a particle by detecting two elements on a particle-by-particle basis within one short sample analysis time. It is expected that the detection of multiple elements in NNPs will distinguish them from the simpler single element detection events characteristic of ENPs. A qualitative validation procedure with the Au-Ag NPs, Au NPs, and Ag NPs (all < 100 nm in size) showed that dual element spICP-MS detected and reported signals for the correct analytes using dwell times and settling times of 100 mus. A quantitative comparison between the single element mode and dual element mode average NP intensities for the Au-Ag NPs showed dual element NP intensities that converged on an average in agreement with the expected core-shell NP mass ratio. The ratio of single element NP intensity to dual element NP intensity was the same for both analytes, which may indicate an empirical factor that can be applied to convert the average NP intensity in dual element mode to a NP mass. Approximately 40% of the dual element NP peaks were false negatives for the detection of particles containing both Au and Ag. Dual element spICP-MS favors false positives for the high abundance element and false negatives for the low abundance element. Future work will aim to broaden the NP peak to obtain more NP readings above the background to reduce false positives and negatives.