NOVELTY - Concentration of low molecular weight alcohol in aqueous solution is measured by: (i) using fuel cell sensor having anode chamber, cathode chamber, and proton conducting membrane; (ii) feeding aqueous solution to anode and cathode chambers; (iii) operating fuel cell sensor in open circuit state; (iv) measuring open circuit voltage across anode and cathode; and (v) determining concentration of the alcohol.    USE - The method is used in the measurement of concentration of low molecular weight alcohol in aqueous solution.    ADVANTAGE - The method uses fuel cell that converts chemical energy directly to electrical energy without undergoing intermediate steps.    DETAILED DESCRIPTION - The measurement of the concentration of low molecular weight alcohol in aqueous solution is measured comprises:    (i) using fuel cell sensor having anode chamber for electrochemical oxidation of the alcohol, cathode chamber for electrochemical reduction of oxygen, proton conducting membrane between the anode and cathode chambers, and voltmeter connected to anode and cathode;    (ii) feeding the aqueous solution to anode and cathode chambers and feeding air to the cathode chamber;    (iii) operating the fuel cell sensor in open circuit state;    (iv) measuring open circuit voltage across anode and cathode using the voltmeter; and    (v) determining the concentration of the alcohol using the open circuit voltage.    The anode and cathode chambers have anode and cathode (7) field plate, anode and cathode (6) gas diffusion layer, and anode and cathode (5) catalyst layer.    An INDEPENDENT CLAIM is also included for a device for measuring the concentration of the low molecular weight alcohol in aqueous solution comprising anode chamber, cathode chamber, proton conducting membrane, voltmeter, and inlet for feeding the solution to the anode chamber and inlet for feeding air to the cathode chamber.    DESCRIPTION OF DRAWING(S) - The figure is a schematic diagram of a direct methanol fuel cell stack system with methanol concentration measurement sensor.    Reservoir (1)    Pump (2)    Cell stack (3)    Tubing (4)    Cathode catalyst layer (5)    Cathode diffusion layer (6)    Cathode flow field plate (7)