Gas chromatographic identification of trace amounts of organic compounds

Methods for the identification of gas chromatographic separated components of essential oils have been investigated. The use of relative retention data was found to be of value for identification only when known standards are available for comparison. Tabulated Kovats indices, available from references, were found to be unreliable for the identification of unknown compounds. These techniques may be of value for preliminary identification of some compounds, however it was found that spectroscopic and chemical reaction data were necessary in order to postively identify unknown compounds. Combined gas chromatography - mass spectrometry computer techniques enabled the rapid identification of the majority of compounds present in these complex mixtures. Compounds identified by this technique were found to be in agreement with many previously identified by retention data. There were limitations in the identification of compounds with similar spectra and the spectra of unknown compounds not being included in the data base. Where other spectroscopic data was necessary for identification purposes, an off-line gas chromatographic sampling device was constructed which enabled the collection of nanogram amounts of compounds eluting from a gas chromatographic column. Compounds collected this way were able to have their Raman spectra recorded without any further sample manipulation. The technique was also used for the recording of infrared, and nuclear magnetic resonance spectra enabling positive identification of some compounds. Techniques of reaction gas chromatography mass spectrometry were developed. Hydrogenation techniques were found useful for the determination of the number of double bonds in a compound whilst carbon skeleton chromatography - mass spectromatry was used for the identification of the hydrocarbon skeleton of unidentified compounds. Subtraction gas chromatography enabled the tentative identification of the alcohol functional group in some compounds. It was concluded that, due to the complex nature of the essential oils investigated, a single technique is not available that enables complete identification of all components. A combination of all these methods must often be used for the complete identification of components in essential oils.