Investigating agglomeration and dissolution of silica nanoparticles in aqueous suspensions by dynamic reaction cell inductively coupled plasma-mass spectrometry in time resolved mode

Dynamic reaction cell inductively coupled plasma-mass spectrometry was used to investigate the behaviour of aqueous suspensions of SiO2 nanoparticles in terms of agglomeration and dissolution, two critical aspects in the evaluation of the potential toxicity of nanomaterials in vitro and in vivo. Polyatomic interferences arising from 12C16O and 14N2 on 28Si were dealt with using methane as reactive gas in the dynamic reaction cell. The agglomeration of four different SiO2 nanomaterials at mass concentrations in the range of 40–400 ng ml−1 was studied by time resolved analysis. The intensities of the transient signals generated by the ionisation of a number of nanoparticles at each given sampling time were recorded in time scan and converted into averaged particle diameters using the reference material ERM-FD 100 as a calibrant. The different agglomeration behaviours exhibited by the various nanomaterials were confirmed by experiments using membrane filtration with selected cut-offs. These experiments also revealed that the nanomaterials showed a 30-fold difference in terms of solubility. Electron microscopy (SEM and TEM), used as the reference technique for measurement of primary particle size and particle size distribution, yielded consistent results highlighting the viability of the analytical approach developed. The method allows for rapid screening of the stability of nanosilica suspensions and monitoring of any changes over time with minimal sample preparation.