preconcentrator having nanoslit structures. A secondary bead bed (PSC/Ag/Au device) yields a comparable CVC to the Ag/Au device, but the currents are shifted lower due to increased overall resistance (black line, Figure ). Finally, in the PSC/Au control, an earlier and abbreviated limiting current regime was observed when compared to the planar Au system (Figure , blue and red trace), while the Ag/Au system shows a direct transition from the ohmic to overlimiting regime (black trace). Based on these results we conclude that the PSC beads reach a mass transport limit more rapidly because the limited interstitial fluid volume is more readily depleted of electrolyte ions. Earlier onset of overlimiting behavior (alternative routes of cation transport to the electrode) in the presence of these negatively charged beads may be attributed to enhanced ion conduction along bead surfaces, enhanced electroosmotic flow, and decreased diffusion length scales between beads. However, the direct transition from ohmic to overlimiting behavior observed at the 3D electrode (Ag/Au case) is characteristic of ICP at a microstructured junction (electrode or membrane) attributed to facile nucleation of fluid vortices.