Book excerpt: This volume details the principles and instrumentation of gas chromatography-mass spectrometry (CG-MS), and outlines industrial, environmental, pharmaceutical, clinical, toxicological, forensic and food-related applications, revealing findings from the laboratories of 40 contributing scientists around the world using GC-MS in practice. It describes upstream and downstream applications of GC-MS in the petroleum industry and identifies chlorinated compounds in the environment with quadrupole ion-trap technology and high-resolution sector instruments.