A high-throughput sample introduction system for chip-based microfluidic analysis was developed. The sampling system was composed of a capillary sampling probe attached to the microchip channel and an array of horizontally positioned micro-sample vials with slits fabricated on the bottom of each vial for pass-through of the sampling probe. The micro-sample vials array was fixed on a homebuilt platform capable of moving linearly under computer control. Sample introduction was performed by linearly moving the array of vials,allowing the probe inlet to sequentially enter the solutions in the vials through the slits. The use of a slotted vial array in the sample introduction system allowed convenient and rapid sample change with low sample volume in 10\+\{-9\} L range and high sampling frequency without requiring mechanical valves and pumps. The system was applied to achieve continuously automated sample change in a chip-based flow injection analysis system with absorption detection by using a liquid-core waveguide capillary flow-cell. High sampling throughput of 600 h -1 was obtained in this system with a sample consumption of only 4.3 nL for each cycle.
In this work, two novel approaches were developed for miniaturized liquid-liquid(L-L) extraction on microfluidic chips, based on a stopped-flow extraction technique. In the first approach, trapped droplets extraction mode, organic solvent droplets of a few hundred 10 -12 L were trapped within micro recesses fabricated in the channel walls of microfluidic chips, and analytes in aqueous streams flowing over the droplets were transferred into them, affecting a preconcentration. In the second approach, a stable interface between stationary organic phase and continuously flowed aqueous phase was formed by stopping the flow of organic phase. Analytes were transferred from the aqueous phase into the organic phase on the interface. Enrichment factors exceeding 1 000 and 300 were achieved with a preconcentration period of 20 min with sample consumption lower than 10 μL for trapped droplets and stopped-flow microextraction. In situ laser induced fluorescence detection of the concentrated analyte was performed following the preconcentration.
