A method is described for the gas chromatographic-electron-capture detection determination of alkenes via on-column bromination reactions. Pyridinium bromide perbromide (PBPB) was used as the Br2 source, and a cholesterol-glass beads mixture, treated with methanol, was used to remove excess Br2. The optimum ratio of cholesterol to glass beads was found to be 1:10, at which 93% of the bromine released from PBPB can be removed, without removal of the derivitized analytes. The conversion efficiency of alkene to the brominated derivative is extremely low (less than 2%) for ethene, whereas for propene and 1-butene it is 41 and 79%, respectively. For C3---C5 alkenes, this method is 200–300 times more sensitive than analysis of the underivitized analytes by using conventional flame ionization detection.