We present a new and simple capillary electrophoresis microsystem in which the sample is injected hydrodynamically using a pressure pulse. This technique maintains the sample composition, in contrast to a classical electrokinetic injection, in which the magnitude of the electric field in the sample reservoir in combination with variations in electrophoretic mobility can lead to a biased injection. The sample is loaded using a well controlled and variable pressure pulse (0.1-1.0 s) generated by the mechanical actuation of a flexible membrane placed on the chip sample reservoir. A fluorescein/calcein-containing borate-Tris-hydroxymethylaminoethane (TRIS) sample solution is taken as a model system for CE analysis. The separation results using pressure pulse injection clearly demonstrate the advantages of our technique. In addition to the reduced bias due to the absence of an electrode in the sample well, this method allows injection of variable plug volumes by simply changing the pulse length. Moreover, a very high speed, repeatability, and sensitivity of the separation is obtained.
We introduce powder blasting for the fabrication of glass microchips. Powder blasting is a fast and cheap technique with which we pattern channels in sodalime and pyrex glass with a width down to 100 mm. We combine the technique with appropriate bonding procedures to realise sealed microchannel structures. We study the transport of¯uorescent dye solutions and¯uorescent beads within channels made by powder blasting and in`classical' channels made by HF-etching. We ®nd a remarkable difference in sign of the electric ®eld induced¯ow for both types of channels and explain the observed strong plug broadening effects in the powder blasted channels. #
Capillary electrochromatography (CEC) appears ideally suited for high performance separations at small scale, i.e. on a chip. Problems with the reproducible production of the required m-HPLC column, but also the lack of commercially available m-CEC instruments have prevented many putative applicants of this promising technique from entering the ®eld. In this paper, a fast and easy way to produce selfcontaining open-tubular m-CEC columns (C 8 -moieties for reversed phase applications) by the sol±gel technique is described. The corresponding chips were designed to be compatible with a commercial system for capillary electrophoresis (namely a Beckman P/ACE 5500 system with diode array detection). Method development and application hence bene®ted from the injection and the detection options of this setup. The separation of a mixture of three uncharged analytes (polycyclic aromatic hydrocarbons) by the chip is given as example. Under optimized conditions, the performance of the chip appeared to be comparable or better than that of capillary-based CEC columns of the same kind. #
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