Continuous monitoring with microfabricated capillary electrophoresis chip devices

We report on the direct coupling of hydrodynamically flowing stream to a microchip capillary electrophoresis (CE) for continuous assays of liquid samples. The new interface relies on mounting the sample tubing onto a sharp inlet tip and allows rapid, convenient and reproducible electrokinetic loading from a continuously flowing stream directly into the narrow separation microchannel. The sharp inlet interface is characterized by its efficiency, stability and simplicity. The effect of the sample flow rate, applied voltages and other relevant variables, is described. It was found that the peak intensity is independent of the flow rate. The performance of the new interface is illustrated for on-line CE-electrochemical monitoring of phenolic and explosive compounds. Conditions simulating continuous long-term monitoring, led to a highly stable response for a 15 ppm 1,3,5-trinitrobenzene solution (RSD = 3.7%, n = 40). Such ability to continuously introduce flowing samples into micrometer channels makes ` lab-on-a-chip' devices highly compatible with real-life monitoring applications.