Identification by GC-MS of cymene isomers and 3,7,7-trimethylcyclohepta-1,3,5-triene in essential oils

摘要

Retention indices of cymene isomers published in popular GC-MS atlases were found to be erroneous by analyzing synthetic samples. The following retention indices (RI) were found using a nonpolar phase (diphenyl: dimethylpolysiloxane, 5:95) for four essential-oil components with indistinguishable mass spectra: 3,7,7-trimethylcyclohepta-1,3,5-triene (RI = 970), m-cymene (RI = 1022), p-cymene (RI = 1024), and o-cymene (RI = 1039). The relative distributions of these compounds were evaluated based on the analysis of about 1000 essential oils. Simple methods were given for preparing standard mixtures of isomeric compounds for identification by GC-MS.