Qualitative Analysis of Monoterpene Isomers by GC-MS with Spectral Similarity Analysis and Retention Index

93 pieces of mass spectra for 37 kinds of monoterpene isomers,collected from the NIST02.L library database,were classified by cluster analysis.The monoterpene isomers were classified into five groups,and most of them were clustered into one group which consisted of 77 pieces of the mass spectra containing 30 kinds of monoterpene isomers.Some of the mass spectra were very similar.It is difficult to identify these compounds only by the traditional mass spectrum search.A new qualitative approach was proposed for the identification of these isomers by retention index and improved spectral similarity analysis,in which the contribution to spectral similarity base peak were eliminated.The differences among the mass spectra of these isomers could be reflected more significantly.This method was applied in the qualitative analysis for the volatile components from Mentha hapioealyx Briq and flavor.Results showed that most of the monoterpene isomers could be identified easily and effectively by the proposed method.