Methodology is presented for the concentration, detection and measurement of vinyl chloride (VC) in water at a maximum sensitivity of 0.1 μg/1 by gas chromatography, using the halogen specific microcoulometric titration detector. The methodology eliminates cyanogen chloride (CNCI) as a potential interference by using a 180 mm × 4 mm i.d. GC column packed in the first one-third with Chromosorb 101, and in the second two-thirds with Chromosorb 102; a procedure for purging the sealed sample bottle itself is utilized as a means of analyzing larger samples, while at the same time avoiding the loss of VC by volatilization which occurred when the sample was tranferred to a purging device. A method of verifying the accuracy of standard solutions that utilizes a new device called a “Reaction Coulometer,” is also included and a detailed description of how to convert the inlet system of the Tracor MT 220 gas chromatograph to a desorbing device is provided.