Measurement of patchouli oil vapor using array of MOS gas sensors in various adulteration substances and concentrations

Abstract

Indonesia is one of the main suppliers of Patchouli oil in the world market. It has high economical value. Indonesian Patchouli oil is mostly produced by SMEs using the distillation technique. However, the high demand and price of Patchouli oil led to the fraud of adulteration. SMEs intentionally mixed Patchouli oil with cheaper oils. This paper presented the vapor measurement of Patchouli oil by using an array of metal oxide semiconductor gas sensors (MOS) which may apply to indicate the presence of adulteration substance in Patchouli oil. A total of nine MOS gas sensors were tested. All MOS are driven with temperature modulation technique. We built an acquisition unit based on the PSoC device to acquire the MOS outputs to a computer. We tested two adulteration substances (palm oil and biodiesel oil), and two compositions (1:3 and 1:5) on two levels of Patchouli oil. Individual response of MOS was examined. The Principle Component Analysis (PCA) method was used to show the classification performance to distinguish the adulteration types in Patchouli oil. We found that there was no single MOS that able to distinguish the adulteration individually, and there were many overlapping responses to adulteration substances and compositions. The PCA results showed that on each level of Patchouli oil, nine MOS gas sensors can distinguish clearly between the with and without adulteration substances (palm oil and biodiesel oil).