Liquid-liquid extraction processes, characterized on-line by instrumented microfluidic platform, significantly enhance the development of predictive thermodynamic models, such as ienaics, and lay the foundations for new approaches to improve kinetic models which combine transport and chemistry. Instrumented microfluidics enables precise measurement of free energy of transfer of species at equilibria and their associated characteristic transfer times, faster and more accurately than its batch mode counterpart. Computer controlled and fully automatized, our platform illustrated the kinetic differences of high extraction's of Ytterbium (Yb) and Iron (Fe), two elements reported as having very different extraction efficiencies due to different molecular forces competing with complexation when modifiers are used together with extractants. Once collected and processed, the kinetics show two distinct behaviors of these two metallic elements: depending on the temperature, Fe could display a very slow extraction profile when compared to Yb. illustrer les fortes différences cinétiques d'extraction de l'ytterbium (Yb) et du fer (Fe), deux éléments pointés pour leur efficacité d'extraction très différente en raison de différentes forces moléculaires rivalisant avec la complexation lorsque des modificateurs sont mis en jeu avec des molécules extractantes. Une fois collectées et traitées, les données cinétiques montrent deux comportements distincts concernant ces deux éléments métalliques: selon la température, Fe peut présenter un profil d'extraction très lent par rapport à Yb. National Environmental Agency (NEA) National Research Foundation (NRF) Published version AM, DM and JCG acknowledge financial support from SCARCE project, which is supported by the Na- tional Research Foundation, Singapore, and National Environment Agency, Singapore under its Closing the Waste Loop Funding Initiative (Award No. USS-IF- 2018-4). JCG acknowledges funding for the microflu- idic platform from the European Research Council under the European Union’s 7th Framework Program (FP/2007-2013)/ERC Grant Agreement N◦ [320915] “REE-CYCLE”: Rare Earth Element reCYCling with Low harmful Emissions. FO thanks CEA’s program “Matériaux et Procédés” for a PhD support (project MICROPRO).