Microchip-based capillary electrochromatography using packed beds

Integration of a packed column onto a microchip for performance of capillary electrochromatography (CEC) is described. The quartz device incorporated a cross-injector, and a double weir trapping design for formation of 1, 2 and 5 mm long CEC columns. Three fluorescent dyes were baseline-resolved with plate numbers of 330 (330000 plates/m; height equivalent to a theoretical plate, H = 3.0 mum) for BODIPY 493/503, 360 (360 000 plates/m; H = 2.8 mum) for rhodamine 123 and 244 (244 000 plates/m; H = 4.1 mum) for acridine orange (AO) with 500 V applied on a 1 mm long column. The 2 mm column yielded similar to1.8 times more theoretical plates than did the 1 mm column, when operated at the same flow rate. Van Deemter plots were obtained for the three column lengths, showing increased plate height for the 5 mm length. A 2 mm column gave peak height and area relative standard deviation (RSD) values of 2.5 and 3.3%, respectively, as averages for the three dyes (n = 15). The RSD for the dye retention times was 1% (n = 6) over one day, and 3% (n = 30) over five days. Indirect fluorescence detection of thiourea and of amino acids was possible using a neutral indicator dye (BODIPY 493/503), with a detection limit of 10 muM for amino acids.