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 el ectrolyte for the amperometric determination of vapor-phase monomethyl hydr azine (MMH). Three detection strategies were tested, namely cyclic voltamme try at a Pt working electrode with the oxidation mediated by Fe-II,Fe-III t hat was hosted by the silica, pulsed electrochemical detection with a Bold working electrode, and potentiostatic oxidation at a mixed-valence rutheniu m oxide (mvRuOx) film that was deposited on a Pt working electrode prior to casting the solid electrolyte overlayer. The sensitivities (and linear dyn amic ranges) for the respective methods were 1.4 nA/ppm (500-1400 ppm), 0.4 9 nA/ppm (70-1050 ppm), and 0.30 nA/ppm (1-1050 ppm). With pulsed electroch emical 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 uncertain ty of the intercept of the Fe-II,Fe-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.