An electric potential was applied to the inlet (∅ = 𝑉 3 ) and the electrodes (planar and Ag microbeads, ∅ = 0). Mass transport across the liquid-PDMS boundary was assumed to be zero (𝚥 ⃗ / • 𝑛 /⃗ = 0). The reaction rate at the electrode surface is faster than mass transport, and therefore, the cation is completely depleted on those surfaces, (𝑐 # = 0). This assumption simplified the simulation while allowing us to ascertain the impact of the packed bed on the system. The simulation was performed for conditions modeling a volumetric flow rate of 100 nL/min and applied potential of 7 V versus ground at the embedded electrode. Table details the boundary conditions used. well-defined and uniform size, less lateral vortex movement, and a more stable mixing layer than was observed at a flat membrane. We anticipated that microstructuring at the electrode surface would accomplish a similar outcome. In Figure , the streamline and the vorticity were extracted from a vertical plane that cuts through the center of the microbeads in the first row of the bed. We see vorticity generated close to (and at) the particle surface (Figure , z = 0.25 of channel width), which is then transported in the lateral direction, as seen in Figure . In Figure , streamlines and vorticity were extracted from a vertical plane that passes between two microbeads. Here, we clearly see vortex formation, however, the size and the magnitude were significantly smaller than those observed in the absence of microbeads. Moreover, the vortices seen in Figure and Figure are small, uniform in size and paired. Therefore, the simulation results confirm that the microstructured electrode limits added Ag microbeads, a high electric field was achieved only at the bottom of the channel (Figure ). In contrast, with added Ag microbeads, a strong electric field was uniformly distributed across the entire channel height. These simulation results are significant because the electric field distribution is an indicator of enrichment performance. ICP enrichment is achieved by countering convective transport by the locally enhanced electric field within the IDZ. Therefore, a higher Figure shows the distribution of ionic strength in the simulated devices with the planar (Figure ) and microstructured 3D (Figure ) electrodes. The ionic strength is near to that of the bulk fluid at the upstream boundary of the simulated domain and transitions abruptly to an IDZ within approx. 100 𝜇m of the planar electrode. However, in the device with conductive microbeads, the vortices create inroads for cation transport to the electrode, which can be observed as narrow extensions of bulk ionic strength across the IDZ. This enhanced mass transport is what facilitates direct transition from ohmic to overlimiting regimes.