Detection of eucalyptus oil adulteration in Australian tea tree oil using UV-Vis and fluorescence spectroscopy

Pure Australian tea tree oil is a high-value commodity; however, cheaper tea tree oils are often adulterated with other substances such as eucalyptus oil. Detection of adulteration typically requires time-consuming analysis with expensive equipment. Consequently, rapid methods of screening for adulteration would be beneficial for the industry. This study examined whether the rapid, non-destructive and low-cost methods of ultraviolet-visible and fluorescence spectroscopy could be used to detect adulteration of tea tree oil with eucalyptus oil. Ultraviolet-visible spectroscopy showed moderate accuracy for predicting adulterant concentration (root mean square error of cross-validation (RMSECV) of 6.8% v/v). Moving window analysis was used to reduce the model wavelength range to just 55 nm, without a loss in predictive accuracy. Fluorescence spectroscopy also performed well, with an RMSECV of 2.9% v/v. Consequently, these techniques may be suitable for rapidly and cheaply screening tea tree oil samples for gross adulteration.