This is a method for determining low concentrations of hydrogen chloride in gas systems, such as Platforming Process recycle gas streams. The lower limit of hydrogen chloride detection varies inversely with gas sample size. At least 40 to 50 cu ft is desired for a lower detection limit of 0.1 mol-ppm hydrogen chloride. The procedures of this method are more rapid than colorimetric or turbidimetric procedures but larger gas samples are required for comparable lower detection limits.