While the application range of SiO2 nanoparticles (SiO2-NPs) is broadening, many of the current and new uses can increase their accumulation in the environment. First predictions for engineered SiO2-NP concentrations in environmental surface water are 0.12 µg/L, and the mean concentration in soil is estimated to be 0.43 µg/L. Therefore, it is crucial to gain more information about the degradation of SiO2-NPs in the environment, which is currently scarce. Here, we present the results of a method development that was used to quantify the dissolution rate of SiO2-NPs in aqueous media. Silica was quantified using inductively coupled plasma optical emission spectroscopy (ICP-OES) and a colorimetric assay. After initial tests of a variety of classic dialysis membrane systems, we adopted a membrane- free system. This allows direct measurements of the unaltered dissolution rate. To validate this setup, we quantified the dissolution SiO2-NPs at pH 11 over 72 h in parallel with a membrane-free and a classical membrane setup. The high pH 11 was chosen because of the known fast base-catalyzed hydrolytic degradation of SiO2 in this pH range. Using an initial concentration of 300 mg SiO2/L, complete dissolution was observed within the first 50 hours in the membrane-free setup. A pseudo-first order kinetics model d (t) = dmax (1-e-kt) fitted to the data, where d is the percentage of dissolved Si and k the dissolution rate constant. The model allowed estimating a half-life of about 10.2 hours for SiO2-NPs in Milli-Q water at pH 11. The particle dissolution was confirmed by TEM micrographs. We currently use this system to evaluate particle dissolution at environmentally relevant pHs. This study shows that membrane-free dissolution systems are a versatile tool to produce data for the fate and behaviour of SiO2-NPs in aqueous media, which is important for the regulation of this nanomaterial.