The increasing manufacture and production of engineered nanomaterials will inevitably lead to their release into the environment. Current analytical techniques lack the required sensitivity and specificity to characterize these materials in complex biological and environmental matrices. In recent years, single particle ICP-MS has been developed as a premiere technique for the analysis of ENMs; harnessing the elemental specificity of mass spectrometry in conjunction with sufficiently low detection limits relevant to environmental release concentrations (ng L<sup>-1</sup>). Though this technique has been shown to successfully characterize metallic and metal oxide nanoparticles in environmental matrices, some common ENMs are comprised of elements that are plagued by abundant molecular interferences when analyzed by ICP-MS. One such ENM, silica, is particularly difficult, as the silicon ion analyte is inundated by the ubiquitous presence of dinitrogen ions of an identical mass-to-charge ratio. This research examines three different approaches for reducing the signal generated by these interfering molecular ions for the purpose of detection and size characterization of silica nanomaterials. Conventional methods of dinitrogen removal are explored using collision and reaction gases. The helium collision cell is able to reduce the interfering signal, but the indiscriminate nature of this approach results in a relatively large size detection limit of 300nm. A more selective approach using a reactive ammonia gas reduces the size detection limit considerably to 200nm, but unavoidable side reactions still limit its applicability. New advances in the data acquisition of ICP-MS have allowed for the implementation of microsecond dwell times. Using these short dwell times, the proportion of silicon ions detected generates a proportionally larger signal that the constant background of interfering molecules. This approach allows for size detection down to approximately 100nm, but also is limited by a number of analytical challenges that need to be considered. Though these techniques are shown to successfully detect and size these particles, more work is needed to improve the sensitivity to silicon ions in order to further improve upon the size detection limit and expand this techniques application to a wider range of silica materials.

Improvements in the detection and characterization of silica nanomaterials using spICP-MS

249th National Meeting (2015)

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