Chemically modified electrodes, which were constructed by anodizing glassy carbon electrodes in a RuC13/&Ru(CN)6 solution, are shown to catalyze the electrooxidation of hydrazine compounds in acidic and neutral media. The mixed-valent ruthenium cyanide film offers improved stability and a broader operational pH range compared to previously described phthalocyanine-catalytic surfaces. The catalytic response of hydrazine, methylhydrazine, and dimethylhydrazine is evaluated with respect to the film preparation conditions, solution pH, potential scan rate, concentration dependence, and other variables. Highly stable and sensitive flow injection measurements [with a relative standard deviation (RSD) of 1.4% ( n = 30) and a detection limit of 0.13 ng] are described. A composite film prepared by the codeposition of polyaniline offers additional advantages.
mTTRODUCTION
Because of the industrial and environmental importance of hydrazine compounds, a highly sensitive method is required for their determination. Voltammetry and amperometric detection for liquid chromatography represent powerful schemes for monitoring easily oxidizable species (e.g., catechols and aromatic amines). Unfortunately, hydrazine compounds have a large overpotential toward electrooxidation at ordinary (unmodified) carbon surfaces and, consequently, are not ideally suited for quantitation via conventional electrochemical approaches. Recent efforts, particularly those of Baldwin [ 1, 21, have been directed toward enhancing the amperometric detection of hydrazine compounds. Carbon