Within the field of microscale or nanoscale chromatography, planar microfluidic devices have been gaining interest in recent years as alternatives to stainless steel, polyether-ether-ketone (PEEK), or fused silica tubes that are traditionally used for chromatography (e.g., high-performance liquid chromatography (HPLC)) and capillary electrophoresis (CE). CE microchips fabricated in glass or polymers allow for the creation of smaller injection plugs, to better dissipate heat arising from Joule heating, and to integrate multiple parallel separation channels into a single planar device. Likewise, in the HPLC and ultra-high performance liquid chromatography (UHPLC) realm, microchips have several advantages over commercially available tubular columns made out of fused silica or PEEK. Those advantages include the integration of a trapping channel on the same device as the analytical channel with minimum dead volume between the two channels, better ease of use, reduction of fluid connections and associated dead volume, and reduced risk of leakage.