Sample filtration, concentration, and separation integrated on microfluidic devices

Microfabricated devices integrating sample filtration, solid-phase extraction, and chromatographic separation with solvent programming were demonstrated. Filtering of the sample was accomplished at the sample inlet with an array of seven channels each 1 mum deep and 18 mum wide. Sample concentration and separation were performed on channels 5 mum deep and 25 mum wide coated with a C18 phase, and elution was achieved under isocratic, step, or linear gradient conditions. For the solid-phase extraction, signal enhancement factors of 400 over a standard injection of 1.0 s were observed for a 320-s injection. Four polycyclic aromatic compounds were resolved by open channel electrochromatography in under 50 s. Chip operation was unaffected by the presence of the 5-mum silica particles at the filter entrance.