Trihalomethanes, such as chloroform ,CHCl3, and bromoform, CHBr3, are found in most chlorinated waters. Because chloroform is a suspected carcinogen, the determination of trihalomethanes in public drinking water supplies is of considerable importance. In this method the trihalomethanes CHCl3, CHBrCl2, CHBr2Cl, and CHBr3are isolated using a liquid–liquid extraction with pentane and determined using a gas chromatograph equipped with an electron capture detector.