Rapid evaluation and quantitative analysis of thyme, origano and chamomile essential oils by ATR-IR and NIR spectroscopy

The essential oils obtained from various chemotypes of thyme, origano and chamomile species were studied by ATR/FT-IR as well as NIR spectroscopy. Application of multivariate statistics (PCA, PLS) in conjunction with analytical reference data leads to very good IR and NIR calibration results. For the main essential oil components (e.g. carvacrol, thymol, gamma-terpinene, alpha-bisabolol and beta-farnesene) standard errors are in the range of the applied GC reference method. In most cases the multiple coefficients of determination (R-2) are >0.97. Using the IR fingerprint region (900-1400 cm(-1)) a qualitative discrimination of the individual chemotypes is possible already by visual judgement without to apply any chemometric algorithms. The described rapid and non-destructive methods can be applied in industry to control very easily purifying, blending and redistillation processes of the mentioned essential oils. (C) 2003 Elsevier B.V. All rights reserved.