Comprehensive two‐dimensional separations based on capillary high‐performance liquid chromatography and microchip electrophoresis

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Abstract
A novel comprehensive two‐dimensional (2‐D) separation system coupling capillary high‐performance liquid chromatography (cHPLC) with microchip electrophoresis (chip CE) is demonstrated. Reversed‐phase cHPLC was used as the first dimension, and chip CE acted as the second dimension to perform fast sample transfers and separations. A valve‐free gating interface was devised simply by inserting the outlet‐end of LC column into the cross‐channel on a specially designed chip. A home‐made confocal laser‐induced fluorescence detector was used to perform on‐chip high‐sensitive detection. The cHPLC effluents were continuously delivered to the chip and pinched injections of the effluents every 20 seconds were employed for chip CE separation. Gradient elution of cHPLC was carried out to obtain the high‐efficiency separation. Free‐zone electrophoresis was performed with triethylamine buffer to achieve high‐speed separation and prevent sample adsorption. Such a simple‐made comprehensive system was proved to be effective. The relative standard deviations for migration time and peak height of rhodamine B in 150 sample transfers were 3.2% and 9.8%, respectively. Peptides of the fluorescein isothiocyanate (FITC)‐labeled tryptic digests of bovine serum albumin were fairly resolved and detected with this comprehensive 2‐D system.