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.