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We present a compact portable chip-based capillary electrop horesis system that employs capacitively coupled contactless conductivity detection (C 4 D) operating at 4 MHz as an alternative detection method compared to the commonly used optical detection based on laser-induced fluorescence. Emphasis was put on system integration and industrial manufacturing technologies for the system. Therefore, the disposable chip for this system is fabricated out of PMMA using injection molding; the electrodes are screen-printed or thin-film electrodes. The system is designed for the measurement of small ionic species like Li + , Na + , K , SO 42- or NO 3- typically present in foods like milk and mineral water as well as acids e.g. in wine. Keywords: polymer chip, electrophoresis, contactless conductivity detection 1. INTRODUCTION Over the last years, chip-based analytical methods, especially chip-based capillary electrophoresis has proven its advantages as an analytical method in a large number of applications, namely the improved speed and the overall simplification in handling of the analytical process [1]. In a ddition, the miniaturisation of the separation column can lead the way to the miniaturization of the complete analytical instrument, paving the road towards a portable analytical system which can be used at the sample si te instead of transferring the sample to the instrument site. Therefore, several concepts of portable instruments have been discussed in the past, mainly in the field of point-of-care diagnostics (POC) [2]. For a wider commercial break-through however, several factors come into play which only recently have received wider attention: The microfabrication methods utilized to manufacture the microfluidic chips have mostly been transferred from the microelectronic world, namely photolithography, wet or dry etching of th e substrate material a nd vacuum deposition of metal films or electrodes. While allowing highly complex geometries with extreme precision, the fabrication cost are prohibitively high for almost any application in routine analysis due to the relatively large footprint of microfluidic devices as compared to microelectronic chips, even more so if a disposable chip is the target of the development. The most widely used detection method for lab-based system s has been laser-induced fluorescence (LIF). While recent advances in solid-state light sources (diode lasers, LEDs) and detectors make this method adaptable to compact, possibly portable systems [3,4], the need for an optical label or dye for most analytical tasks, requires a sample preparation step prior to analysis and often is not possible for smaller ions. In most of the academic work, emphasis was put on the design of the microchip and the optim ization of the application, utilizing detached lab-based external com ponents like power supplies, electrical or fluidic interfaces and mechanical chip holders for the experimental set-up. For a truly portable system which can be used in the field however, a holistic approach has to be taken, integrating all these components together with the microfluidic chip into a complete system. |
