Qualify Investigation and Detection of Major Constituents of Peppermint (Mentha piperita L.) Essential oil by Physical Methods as an Alternative to GC-MS

This article deals with evaluate the purity and detection of peppermint essential oil compositions using different spectrometry and refraction spectrometry methods and to compare them with chromatography. The conventional method for identifying and analyzing essential oils is a costly gas chromatography-coupled mass spectrometer. For this purpose, peppermint essential oil extract was first extracted and its main constituents were identified by chromatogram, menthol and menthon. Then using fast and low cost Raman spectroscopy method with three different spectrometers, two compounds of menthon and menthol were determined. Refractometry and FTIR spectroscopy were used to evaluate the purity of peppermint essential oil. Concentrations of 20, 30, 40, 60, 80 and 90 peppermint essential oils were manually made by cyclohexane solvent. These different concentrations and sample were tested by Refractometry and FTIR spectroscopy. As the results show, infrared spectroscopy is not capable of quantitatively identifying the essence of pure peppermint and its diluted concentrations and is only capable of qualitatively identifying different molecules, but can be clearly distinguishable by the use of refractive index analysis of different concentrations and pure samples. Therefore, Raman spectroscopy and refractive analysis is a fast and inexpensive method capable of identifying the major constituents and determining the purity of the essential oils.