Mediated Oxidation and Determination of Gaseous Monomethyl Hydrazine in a Solid-State Voltammetric Cell Employing a Sol-Gel Electrolyte

Mesoporous silica that was prepared by a sol-gel process was used as the electrolyte for the amperometric determination of vapor-phase monomethyl hydrazine (MMH). Three detection strategies were tested, namely cyclic voltammetry at a Pt working electrode with the oxidation mediated by FeII,III that was hosted by the silica, pulsed electrochemical detection with a gold working electrode, and potentiostatic oxidation at a mixed-valence ruthenium oxide (mvRuOx) film that was deposited on a Pt working electrode prior to casting the solid electrolyte overlayer. The sensitivities (and linear dynamic ranges) for the respective methods were 1.4 nA/ppm (500–1400 ppm), 0.49 nA/ppm (70–1050 ppm), and 0.30 nA/ppm (1–1050 ppm). With pulsed electrochemical detection and mvRuOx, respective detection limits of 20 ppm and 0.3 ppm were calculated on the basis of a concentration that yielded a response three times the standard deviation of the blank. Because of high uncertainty of the intercept of the FeII,III-mediated method, a detection limit was not calculated for this technique. A cell design that provided a three-phase boundary at a mvRuOx-modified electrode yielded a response of 90 % of the steady-state current at 11 s.