An indirect sensing method is described for vinyl chloride with an amperometric sensor connected to a prepyrolysis column. Significant sensing ability to the pyrolyzed gas, produced from pyrolysis of 0-30 ppm vinyl chloride gas, was obtained with a Pt/porous alumina substrate assembly. Furthermore, the sensing current was proportional to the concentration of vinyl chloride gas in the investigated concentration range. The sensitivity and sensing limit for vinyl chloride were observed as functions of pyrolysis temperature, gas flow rate, and applied potential. Preferable sensing parameters were 400degreesC, 150 mL min(-1), and 1.2 V (vs. Ag/AgCl), in which the sensing reaction was controlled by gas diffusion. Effect of porosity of porous alumina substrate on the sensing performances was also studied. The electroactive species, which was contained in the pyrolyzed gas and electrochemical oxidized on the sensing electrode, was suggested to be hydrogen chloride vapor. (C) 2003 The Electrochemical Society.