A high-throughput continuous sample introduction interface for microfluidic chip-based capillary electrophoresis systems.

The development of efficient sample introduction and pretreatment systems for microfluidic chip-based analytical systems is important for their application to real-life samples. In this work, world-to-chip interfacing was achieved by a novel flow-through sampling reservoir featuring a guided overflow design. The flow-through reservoir was fabricated on a 30 x 60 x 3 mm planar glass chip of crossed-channel design used for capillary electrophoresis separations. The 20-microL sample reservoir was produced from a section of plastic pipet tip and fixed at one end of the sampling channel. Sample change was performed by pumping 80-microL samples sandwiched between air segments at approximately 0.48 mL/min flow rate through the flow-through reservoir, introduced from an access hole on the bottom side of the chip. A filter paper collar wrapped tightly around the reservoir guided the overflowing sample solution into a plastic trough surrounding the reservoir and then to waste. The performance of the system was demonstrated in the separation and determination of FITC-labeled arginine, glycine, phenylalanine, and glutamic acid with LIF detection, by continuously introducing a train of different samples through the system without electrical interruption. Employing a separation channel of 4 cm (2-cm effective separation length) and 1.4-kV separation voltage, maximum throughputs of 80/h were achieved with <4.1% carryover and precisions ranging from 1.5% for arginine to 2.6% RSD (n = 11) for glycine. The sampling system was tested in the continuous monitoring of the derivatizing process of amino acids by FITC over a period of 4 h, involving 166 analytical cycles. An outstanding overall precision of 4.8% RSD (n = 166) was achieved for the fluorescein internal standard.