Differential NMR and chromatography for the detection and analysis of adulteration of vetiver essential oils

Adulteration of essential oils is a common and serious problem. Adequate and fast methods are required to establish the authenticity and purity. GC-MS, H-1 and C-13 NMR were compared in combination with similarity calculations as well as differential spectroscopy and chromatography for the authentication and determination of purity of vetiver essential oils. In the investigation of eight commercial oils H-1 and C-13 NMR adequately detected all six adulterants encountered in four of the commercial samples, while GC-MS was not able to detect adulteration with vegetable oils. A great advantage of the combined use of similarity calculation and NMR is that the authenticity can be verified without the need of concomitant measurement of a standard sample. The calculation can be carried out with a registered reference spectrum, in the case of 1H NMR acquired using the same magnetic field, but in the case of C-13 NMR the spectrum can be obtained with another magnetic field. H-1 NMR has the advantage of high speed, and the results can be obtained within minutes. C-13 NMR was found to be superior in its ability to provide unequivocal identification of eventual adulterants, with differential spectroscopy revealing all signals of the adulterants.