A multi-microelectrode device with an internal referencing system for use as an electrochemical sensor

A multi-microelectrode device was constructed and tested as an electrochemical sensor employing a novel system for referencing electrochemical potential. The multi-microelectrode device consisted of three electrodes: (1) a poly(vinylferrocene) ring-modified carbon fiber (Standard Working Electrode, SWE), (2) a silver wire coated with silver chloride (Ag/AgCl reference electrode; Practical Reference Electrode, PRE) and (3) a carbon fiber.^ This self-contained electrochemical device had an internal referencing system. Two types of measurements were made for the purpose of referencing potentials: (1) the peak potential of the ferrocene/ferrocenium redox couple in the SWE versus a Saturated Calomel Electrode (SCE) and (2) the peak potential of the SWE versus the PRE. The difference between these two peaks was calculated and used to report results of electrochemical measurements versus an SCE, a standard reference electrode.^ Differential Pulse Anodic Stripping Voltammetry (DPSV) was used to illustrate this new approach. Various concentrations (0 to 1M) of added chloride ions were used to demonstrate the stability of the peak potential of the SWE versus the SCE and the use of the shift in peak potential for the SWE for calibrating the PRE in situ. Utilizing DPSV, the self-contained device was used to measure concentrations of lead and cadmium ions in the part per billion range. Chloride ion concentration could also be determined using the device in a pseudo-potentiometric technique. A plot of the cathodic peak potential for the SWE versus the activity of various chloride ions showed Nernstian behavior, indicating that unknown chloride ion activities could readily be determined. Concentrations could be obtained using either a calibration curve or standard addition.^ The multi-microelectrode device was modified as an electrochemical detector for use in a commercial thin-layer cell used in High Performance Liquid Chromatography (HPLC). A hydrodynamic voltammogram and chromatograms were obtained for the detection of hydrazine.^ This self-contained electrochemical device eliminates the dependence on conventional reference electrodes that contain salt bridges which can leak and clog. Proven to be versatile, reliable, inexpensive, and easy to maintain, this multi-microelectrode device was designed to make electrochemistry more accessible and more user-friendly to analytical, clinical, and other research chemists.