Development of a Microfabricated Palladium Decoupler/Electrochemical Detector for Microchip Capillary Electrophoresis Using a Hybrid Glass/Poly(dimethylsiloxane) Device

The fabrication and evaluation of a palladium decoupler and working electrode for microchip capillary electrophoresis (CE) with electrochemical detection is described. The use of the Pd decoupler allows the working electrode to be placed directly in the separation channel and eliminates the band-broadening characteristic of the end-channel configuration. The method used for fabrication of the decoupler and working electrode was based on thin-layer deposition of titanium followed by palladium onto a glass substrate. When employed as the cathode in CE, palladium absorbs the hydrogen gas that is generated by the hydrolysis of water. The effect of the decoupler size on the ability to remove hydrogen was evaluated with regard to reproducibility and longevity. Using boric acid and TES buffer systems, 500 μm was determined to be the optimum decoupler size, with effective voltage isolation lasting for ∼6 h at a constant field strength of 600 V/cm. The effect of distance between the decoupler and working electrode on noise and resolution for the separation of dopamine and epinephrine was also investigated. It was found that 250 μm was the optimum spacing between the decoupler and working electrode. At this spacing, laser-induced fluorescence detection at various points around the decoupler established that the band broadening due to pressure-induced flow that occurs after the decoupler did not significantly affect the separation efficiency of fluorescein. Limits of detection, sensitivity, and linearity for dopamine (500 nM, 3.5 pA/μM, r 2 = 0.9996) and epinephrine (2.1 μM, 2.6 pA/μM, r 2 = 0.9996) were obtained using the palladium decoupler in combination with a Pd working electrode.