A three-dimensionally adjustable amperometric detector for microchip electrophoretic measurement of nitroaromatic pollutants

A microchip capillary electrophoresis (CE)–amperometric detection (AD) system has been fabricated by integrating a two-dimensionally adjustable CE microchip and an amperometric detection cell containing a one-dimensionally adjustable disc detection electrode in a Plexiglas holder. It facilitates the precise three-dimensional alignment between the channel outlet and the detection electrode without a complicated three-dimensional manipulator. The performance of this unique system was demonstrated by separating four nitroaromatic pollutants (nitrobenzene, 2,4-dinitrotoluene, 2,4,6-trinitrotoluene, and p-nitrobenzene). Factors influencing their separation and detection processes were examined and optimised. The four analytes have been well-separated within 120 s in a 75 cm long separation channel at a separation voltage of +2000 V using an electrophoretic separation medium containing 15 mM borax and 15 mM sodium dodecyl sulfate (pH 9.2). Highly linear response is obtained for the four analytes over the range of 0–5 ppm with the detection limits ranging from 12 to 52 ppb. The present system demonstrated long-term stability and reproducibility with relative standard deviations of less than 5% for the peak current (n = 9). The new approach for the microchannel–electrode alignment should find a wide range of applications in other microfluidic analysis systems.