Enantiomeric composition of the principal components of the oil of Melaleuca alternifolia

The concentrations and enantiomeric purity of the major monoterpene constituents in a number of Melaleuca alternifolia (tea tree) oils have been determined by enantioselective gas chromatography. Consistent enantiomeric ratios of 65:35 (+:-) for terpinen-4-ol and 76:24 (+:-) for α-terpineol were observed for the range of oils analyzed. Attempts to validate these ratios in the intact oil by 1H NMR together with chiral lanthanide shift reagents have not yet been successful. 1H NMR was, however, successful in confirming the enantiomeric purity determined by gas chromatography of standard terpinen-4-ol [79:21 (+:-)] and α-terpineol [35:65 (+:-)] samples. Under the correct conditions, a single analysis on a β-cyclodextrin column enables the determination of the quality of the oil as set forth by the Australian standard and provides additional enantiomeric evidence of the authenticity of the oil.