Quality control of Austrilian tea tree oils and commercial products using GC/MS and chemometrics

Conventional GC/MS, chiral GC/MS and chemometrics were used to evaluate the quality of known provenance tea tree oils and commercial products. Fifty-eight Australian tea tree oils and 47 commercial products were investigated. Twenty terpenes were determined in each sample and compared with the ISO-4730 – 2004 standards. Several of the oil samples that were ISO compliant when distilled did not meet the ISO standards primarily due to oxidation of the oil samples. Forty-eight percent of the commercial products did not meet the ISO specifications. Four chiral components, α-pinene, limonene, terpinen-4-ol and α-terpineol, present in tea tree oils were measured by chiral GC/MS. The results clearly indicated that 28 commercial products contained excessive (+) isomer or contained the (+) isomer in concentrations below the norm of the known provenance essential oils. Of the 28 outliers, 8 met the ISO standards. A class prediction model was constructed and used to evaluate the commercial products. The outliers identified by the class predictive model coincided with the samples that displayed an abnormal chiral ratio for chiral analysis. Thus, chiral GC/MS and chemometrics could be used for the identification of substandard commercial products including those that met all of the ISO standards.