The downscaling of analytical steps commonly carried out in laboratories results in the reduction of material consumption and waste production, which is of major interest, particularly in the nuclear sector. In this context, we focus on the miniaturisation of the solid phase extraction-based purification steps of samples containing radionuclides. Protocols already exist using cartridges packed with commercial resins before offline multielemental characterization by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) but exhibits additional drawbacks, such as samples of variable levels of radiation. The aim of this study was to develop a miniaturised extraction device based on monolithic porous supports and its coupling to ICP-MS, in order to carry out online, downscaled analysis of nuclear samples. Monolithic porous polymers are an efficient way for reducing the format of the extraction support, thanks to their high specific surface area, adjustable morphology and permeability, as well as the possibility to synthesize them in-situ in either capillaries or microfluidic channels.