Solid-phase microextraction (SPME) in combination with gas chromatography-mass spectrometry (GC-MS) was applied to study the impurities in industrial caprolactam produced from toluene. Various nitriles, lactones, amides, and alcohols were detected to be the main impurities in caprolactam products. Trace amounts of heterocyclic compounds, which had great effects on the quality of caprolactam, were also successfully detected. Those were pyrrole, 2-ethyl-3-methyl pyrazine, 5,6,7,8-tetrahydroquinoxaline, quinoxaline, 2,3-dimethyl quinoxaline, 2-pyridinamide, etc. The effects of some impurities on caprolactam quality and the polymerization of caprolactam as well as the possible origin of the main impurities were also discussed. This could be of great importance to the industrial purity control of caprolactarn. (c) 2006 Wiley Periodicals, Inc.