Determination of methane and other small hydrocarbons with a platinum-Nafion electrode by stripping voltammetry

Methane in the gas phase is determined via pre-adsorption on a dispersed pl atinum electrode backed by a solid polymer electrolyte (SPE) membrane (Nafi on) which is in contact with 10 M sulfuric acid. The adsorption process is strongly temperature dependent with an activation energy of 8.7 kcal mol(-1 ). Prior to the anodic stripping step the platinum electrode is flushed wit h nitrogen resulting in an acceptable selectivity against electroactive spe cies which could otherwise interfere. During the anodic sweep the adsorbed methane is oxidized at the potential of the onset of the formation of the p latinum oxide monolayer. Using a sensing electrode thermostatted at 348 K, a linear calibration curve was obtained from 0.1 up to 5% CH4 in nitrogen, with a detection limit of 130 ppm (S/N = 3), The determination of ethane, p ropane and butane was also found possible by this scheme and the cross-sens itivity to carbon monoxide and hydrogen could be significantly reduced by m eans of suitable chemical adsorption filters. (C) 2001 Elsevier Science B.V . All rights reserved.