Automated sampling system for the analysis of amino acids using microfluidic capillary electrophoresis

An improved automated continuous sample introduction system for microfluidic capillary electrophoresis (CE) is described. A sample plate was designed into gear-shaped and was fixed onto the shaft of a step motor. Twenty slotted reservoirs for containing samples and working electrolytes were fabricated on the "gear tooth" of the plate. A single 7.5-cm long Teflon AF-coated silica capillary serves as separation channel, sampling probe, as well as liquid-core waveguide (LCW) for light transmission. Platinum layer deposited on the capillary tip serves as the electrode. Automated continuous sample introduction was achieved by scanning the capillary tip through the slots of reservoirs. The sample was introduced into capillary and separated immediately in the capillary with only about 2-nL gross sample consumption. The laser-induced fluorescence (LIF) method with LCW technique was used for detecting fluorescein isothiocyanate (FITC)-labeled amino acids. With electric-field strength of 320 V/cm for injection and separation, and 1.0-s sample injection time, a mixture of FITC-labeled arginine and leucine was separated with a throughput of 60/h and a carryover of 2.7%.