NOVELTY - Method of simultaneously quantifying alkane and oxygen using single sensor (10') is performed by supplying alkane gas to interface between activated surface of platinum or palladium working electrode (14) and ionic liquid electrolyte (20), supplying alkane gas in the presence of oxygen to interface, applying positive electrode potential to platinum or palladium working electrode, quantifying concentration of alkane using alkane anodic current or alkane anodic current density at positive electrode potential, and using alkane as internal standard to calibrate oxygen detection.    USE - Method of simultaneously quantifying alkane and oxygen using single sensor for electrocatalysis applications, harnessing methane for energy storage, conversion, or synthesis, making methane-based fuel cells, and/or developing methane sensors.    ADVANTAGE - Potentially interfering species, such as water vapor in the surrounding atmosphere, are kept from interfering with the reactions taking place at the interface between the electrode and the ionic liquid.    DETAILED DESCRIPTION - Method of simultaneously quantifying alkane and oxygen using single sensor (10') is performed by supplying alkane gas to interface between activated surface of platinum or palladium working electrode (14) and ionic liquid electrolyte (20) in which alkane adsorbs at or near interface complex formed at interface and ionic liquid electrolyte is selected from 1-ethyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-pentyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl)imide, 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-heptyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl)imide, 1-octyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-nonyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl)imide, and/or 1-decyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, supplying alkane gas in the presence of oxygen to interface, applying positive electrode potential to platinum or palladium working electrode to cause oxidation of adsorbed alkane and form reaction product, quantifying concentration of alkane using alkane anodic current or alkane anodic current density at positive electrode potential, and using alkane as internal standard to calibrate oxygen detection.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional schematic diagram of an electrochemical sensor.    Sensor (10')    Platinum or palladium working electrode (14)    Reference or quasi-reference electrode (16)    Counter electrode (18)    Ionic liquid electrolyte (20)