Quality control analysis of high-value agarwood oil by thermogravimetric analysis (TGA)

Adulteration is a crucial issue being faced by essential oil and allied industries, especially for high-value essential oil such as agarwood oil. The recommended analysis in trading essential oils involves visual inspection, olfactory analysis, physico-chemical characterization and gas chromatography coupled with mass spectroscopy (GC–MS). However, some subtle high-boiler adulterants like vegetable oils and synthetic polymers go unnoticed via these analyses leading to the penetration of adulterated essential oil in the market. In the current study, the thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA) were utilized and suggested as a rapid, convenient and precise technique for the detection of high-boiler adulterants in essential oils using the most expensive agarwood oil as a case study. The TGA pattern of pure samples reveals single-stage volatilization (agarwood oil: 110–260°C, castor oil: 340–500°C, coconut oil: 330–450°C and polyethylene glycol-400: 260–390°C), whereas the adulterated sample exhibits two-stage volatilization in both lower- and higher-temperature zone owing to the presence of agarwood oil and high-boiler adulterant. The DTGA of pure agarwood oil shows only one point of major weight loss, whereas that of the adulterated sample shows two points of major weight loss corresponding to both oil and adulterant. Different percentages of adulterants (5%, 10%, 30% and 50%) have been quantified using TGA and DTGA with the highest accuracy. Further, the method optimization study was conducted to determine the minimum time required for adulterated sample analysis with precise accuracy. TGA can be proposed as a handy and efficient tool for the quality control analysis of essential oils.