NMR spectroscopy is a powerful tool for the fingerprint analysis of natural extracts as well as of essential oils and could be very useful to assess quality of herbal drugs [1–5]. In this communication, we report the preliminary results of our study on the chemical composition of some essential oils determined by means of GC, GC-MS and NMR spectroscopy. The essential oils were obtained by steam distillation of the following Senegalese plants: Eucalyptus camaldulensis, Fagara leprieurii, Hyptis suaveolens, Lippia chevalieri, Melaleuca leucadendron, Mezoneuron benthamianum, Ocimum gratissimum, Ocimum canum, Xylopia aethiopica, and Citrus aurantium (Petitgrain de bigarade). Oils were preliminarily analysed by GC-MS and quantitative determinations were performed by GC-FID. 1H, 13C, and bidimensional NMR experiments (HMQC HMBC COSY, TOCSY and NOESY) were used to determine the chemical structures of compounds in the crude oil. Quantitative determinations of the selected constituents were obtained using caffeine as internal standard. For example thymol (39.6%), γ-terpinene (19.2%) and p-cymene(11.2%) were determined as main constituents of Ocimum gratissimum, while major components of Xylopia aethiopica oil were identified as β-pinene (35.4%), β-terpinene (16.5%) and α-pinene (13.4%). The obtained results show that NMR spectroscopy is a good analytical tool for both qualitative and quantitative analysis of some of the investigated essential oils, offering advantages over the classical chromatographic methods.
References: [1] Bilia A.R. et al. (2002) J. Agric. Food. Chem. 50: 5016–25. [2] Rivero-Cruz B. et al. (2006) J. Nat. Prod. 69: 1172–76. [3] Guerrini A. et al. (2006) J. Agric. Food Chem. 54: 7778–88. [4] Al-Burtamani S.K.S. et al. (2005) J. Ethnopharmacol. 96: 102–117. [5] Kubeczka K.H., Formàcek V., (2002) Essential oil analysis by capillary GC and Carbon-13 NMR spectroscopy, 2nd Ed., Wiley: New York.
