Underivatized cyclic olefin copolymer as substrate material and stationary phase for capillary and microchip electrochromatography

We report, for the first time, the use of underivatized cyclic olefin copolymer (COC, more specifically: Topas) as the substrate material and the stationary phase for capillary and microchip electrochromatography (CEC), and demonstrate chromatographic separations without the need of coating procedures. Electroosmotic mobility measurements in a 25 μm id Topas capillary showed a significant cathodic EOF that is pH-dependent. The magnitude of the electroosmotic mobility is comparable to that found in glass substrates and other polymeric materials. Open-tubular CEC was employed to baseline-separate three neutral compounds in an underivatized Topas capillary with plate heights ranging from 5.3 to 12.7 μm. The analytes were detected using UV absorbance at 254 nm, thus taking advantage of the optical transparency of Topas at short wavelengths. The fabrication of a Topas-based electrochromatography microchip by nanoimprint lithography is also presented. The microchip has an array of pillars in the separation column to increase the surface area. The smallest features that were successfully imprinted were around 2 μm wide and 5 μm high. No plasma treatment was used during the bonding, thus keeping the surface properties of the native material. An RP microchip electrochromatography separation of three fluorescently labeled amines is demonstrated on the underivatized microchip with plate heights ranging from 3.4 to 22 μm.