Carbon nanotube stationary phases for microchip electrochromatography

The use of nanomaterials in separation science has increased rapidly in the last decade. The reason for this is to take advantage of the unique properties of these materials, such as a very high surface-to-volume ratio and favourable sorbent behaviour. Carbon nanostructures, such as carbon nanotubes are very interesting for integration in especially microfluidic devices, because they can readily be grown on planar substrates by means of chemical vapour deposition. In this way the cumbersome process of packing of the stationary phase in the finished microfluidic channels is avoided and the CNT surface can furthermore be used directly as a stationary phase in reverse-phase separations, thereby avoiding subsequent functionalization of the nanostructures. This significantly reduces the fabrication time and possibly also increases the reproducibility of the column performance. In this presentation, microfluidic devices with microfabricated carbon nanotube columns for electrochromatographic separations will be presented. The electrically conductive carbon nanotube layer has been patterned into hexoganol micropillars in order to support electroosmotic flow without forming gas bubbles from electrolysis of the buffer solution. The device performance is evaluated by chromatographic separation of neutral coumarin dyes.