<p>The work presents the results of numerical simulations of a microdevice designed to concentrate a low-concentration analyte consisting of weakly charged macromolecules. The microdevice consists of a spherical chamber containing an ion-selective sphere located in the center. A gravity-induced pressure-driven flow of an electrolyte solution containing the analyte is established through the chamber. Two electrodes are placed at the input and output of the device to create an external electric field. The properties of the analyte typically differ from those of the ions in the buffer electrolyte solution; for instance, its diffusion coefficient is normally much smaller than those of the electrolyte ions. This asymmetry, combined with a nontrivial electroosmotic flow along the ion-selective sphere, results in significant differences in the analyte behavior compared with the behavior of ions. Several scenarios of analyte concentration, based on both its intrinsic properties (different diffusion coefficients and charges) and external factors such as the intensity of an external electric field and the properties of the flow, are investigated.</p>