  We develop the first theoretical model for the analytical description of ion
concentration polarization (ICP)-based electrokinetic molecular concentration,
which had not been possible due to the extraordinary complexity of the system.
We define the two separate limits for the enrichment factor achievable in a
given system and derive the scaling laws for critical parameters, which are
validated by numerical simulations and experiments. This work provides clear
theoretical explanations on the diverse experimental behaviors previously
observed yet unexplainable, while setting solid foundation for the engineering
of ICP-based concentrators and other fluid-coupled electrokinetic systems.
