I have magnetic silica particles to be tested in r2 relaxometery in MRI. To know [Fe] (Molar) of samples, I must digest the particles for further ICP analysis. How can I dissolve them?
Dissolve the iron off a known mass of the substrate with hydrochloric acid and filter to remove particles and dilute accordingly for your ICP. You don't need to dissolve the silica as its [100% - %Fe3O4] (unless you have other materials present).
It should be noted that silica here is the shell and we need to remove it to access magnetite nanopaerticles in core, then dissolve them by something like HCl.