The Stӧber process is commonly used for synthesising spherical silica particles. This article reports the first
comprehensive study of how the process variables can be used to obtain monodispersed particles of specific
size. The modal particle size could be selected within in the range 20 – 500 nm. There is great therapeutic
potential for bioactive glass nanoparticles, as they can be internalised within cells and perform sustained
delivery of active ions. Biodegradable bioactive glass nanoparticles are also used in nanocomposites.
Modification of the Stӧber process so that the particles can contain cations such as calcium, while maintaining
monodispersity, is desirable. Here, while calcium incorporation is achieved, with a homogenous distribution,
careful characterisation shows that much of the calcium is not incorporated. A maximum of 10 mol% CaO can
be achieved and previous reports are likely to have overestimated the amount of calcium incorporated.