An array of ordered pillars with retentive properties for pressure-driven liquid chromatography fabricated directly from an unmodified cyclo olefin polymer

The current paper describes the development and characterization of a pillar array chip that is constructed out of a sandwich of cyclo olefin polymer (COP) sheets. The silicon master of a 5 cm long pillar array was embossed into the COP, yielding 4.3 µm deep pillars of 15.3 µm diameter with an external porosity of 43 % and a well designed sidewall region to avoid side wall induced band broadening. A closed channel configuration was obtained by pressure assisted thermal bonding to a non-processed COP lid. Injection of coumarin dye plugs and detection with a fluorescence microscope showed very close agreement of this channel configuration to theoretical expectations in terms of band broadening. This agreement is due to the low taper, the optimized sidewall region and the excellent bonding quality between the two polymer sheets, even at the pillar area. Under non-retained conditions (pure methanol as mobile phase), plate heights as low as 4 µm were obtained. Under retained conditions, using the native hydrophobic properties of the COP channel (in 70/30 v/v water/methanol mixture as mobile phase), a minimum plate height of 6 µm was obtained. A 4 component separation was successfully achieved, demonstrating that COP is a cheap and efficient alternative for silicon and silica based liquid chromatography formats.