Capillary Electrophoresis with Direct and Contactless Conductivity Detection on a Polymer Microchip

Abstract

A new, miniaturized conductivity detector for capillary electrophoresis is described, which is directly integrated on a polymer microchip. The chip is fabricated by hot embossing of a PMMA substrate and sealed with a thin cover plate of the same material. The cover plate contains sputtered platinum electrodes for detection and also for high voltage power supply. Two different conductivity detectors are integrated on one single chip: direct and contactless conductivity detection. Both detectors are used on-column, i.e. inside the separation channel. The performance of both detectors is compared using inorganic cations and anions as test analytes. Direct conductivity detection is more sensitive, while the advantage of the contactless detector is that electrode fouling, which may result from direct galvanic contact to complex matrices, is prevented. Detection limits are 12 fmol for direct conductivity detection and 25 fmol for contactless conductivity detection, respectively. The separation of organic acids in wine is demonstrated as analytical application of the microchip.