A microchip electrophoresis device with integrated electrochemical detection: A direct comparison of constant potential amperometry and sinusoidal voltammetry

A microchip electrophoresis system with integrated electrochemical detection is described in this work. The hybrid device utilizes poly(dimethylsiloxane) as the electrophoresis channel substrate and a planar gold electrode lithographically fabricated onto a glass slide for electrochemical detection. The system is characterized by the separation and detection of various neurotransmitters. The gold working electrode is placed just inside the separation channel without adverse effects on the detection sensitivity, due to the electrical decoupling of the detection and electrophoresis systems. The close proximity of the working electrode to the exit of the separation channel results in symmetric peak shapes and efficient separations (50 000- 100 000 plates/m). A direct comparison between the frequency-based electrochemical technique, sinusoidal voltammetry, and the more commonly used constant potential (DC) amperometry is made. Sinusoidal voltammetry is found to be roughly an order of magnitude more sensitive than DC amperometry, with calculated mass detection limits (S/N = 3) of 12 amol and 15 amol for dopamine and isoproterenol, respectively.