The extraction of Eu(III) from medium acidic nitrate solutions with supported liquid membranes (SLMs) was studied with the cavitand-based Carriers 1-3. The experimental time-dependent Eu(III) concentrations were on-line monitored with a radiotracer, the concentration profiles can be described with a non-steady state model. The membrane diffusion coefficients D-m were directly determined from the experimental data. Evaluation of the rate-limiting step showed that aqueous diffusion plays a significant role and that the SLM and the solvent extraction (SX) models are in good agreement. The new immobilized phase solvent extraction (IPSE) system is based on the SLM principle and is a versatile technique for (semi-)continuous extraction of cations.