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Planta Med 2018; 84(12/13): 953-963
DOI: 10.1055/a-0605-3967
Natural Product Chemistry and Analytical Studies
Original Papers
Georg Thieme Verlag KG Stuttgart · New York

Is Low-field NMR a Complementary Tool to GC-MS in Quality Control of Essential Oils? A Case Study: Patchouli Essential Oil[*]

Andre Krause
1   Laboratory of Organic Chemistry, Wageningen University, Wageningen, The Netherlands
,
Yu Wu
2   Chemmind Technologies, Beijing, China
,
Runtao Tian
2   Chemmind Technologies, Beijing, China
,
Teris A. van Beek 
1   Laboratory of Organic Chemistry, Wageningen University, Wageningen, The Netherlands
› Author Affiliations
Further Information

Publication History

received 03 February 2018
revised 27 March 2018

accepted 06 April 2018

Publication Date:
24 April 2018 (online)

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Abstract

High-field NMR is an expensive and important quality control technique. In recent years, cheaper and simpler low-field NMR has become available as a new quality control technique. In this study, 60 MHz 1H-NMR was compared with GC-MS and refractometry for the detection of adulteration of essential oils, taking patchouli essential oil as a test case. Patchouli essential oil is frequently adulterated, even today. In total, 75 genuine patchouli essential oils, 10 commercial patchouli essential oils, 10 other essential oils, 17 adulterants, and 1 patchouli essential oil, spiked at 20% with those adulterants, were measured. Visual inspection of the NMR spectra allowed for easy detection of 14 adulterants, while gurjun and copaiba balsams proved difficult and one adulterant could not be detected. NMR spectra of 10 random essential oils differed not only strongly from patchouli essential oil but also from one another, suggesting that fingerprinting by low-field NMR is not limited to patchouli essential oil. Automated chemometric evaluation of NMR spectra was possible by similarity analysis (Mahalanobis distance) based on the integration from 0.1 – 8.1 ppm in 0.01 ppm increments. Good quality patchouli essential oils were recognised as well as 15 of 17 deliberate adulterations. Visual qualitative inspection by GC-MS allowed for the detection of all volatile adulterants. Nonvolatile adulterants, and all but one volatile adulterant, could be detected by semiquantitation. Different chemometric approaches showed satisfactory results. Similarity analyses were difficult with nonvolatile adulterants. Refractive index measurements could detect only 8 of 17 adulterants. Due to advantages such as simplicity, rapidity, reproducibility, and ability to detect nonvolatile adulterants, 60 MHz 1H-NMR is complimentary to GC-MS for quality control of essential oils.

Key words

essential oil - quality control - 60 MHz 1H-NMR - adulteration - fingerprinting - chemometrics - patchouli

* Dedicated to Professor Dr. Robert Verpoorte in recognition of his outstanding contribution to natural products research.


Supporting Information

    Fig. 1a – fS: 60 MHz and 600 MHz 1H-NMR spectra of standard PEO used for deliberate adulteration; Fig. 2a – hS: effect of viscosity of EOs on NMR spectra; Fig. 3S: 60 MHz 1H-NMR spectra of a severely adulterated viscous PEO; Fig. 4a – bS: 600 MHz 1H NMR of patchoulol and 60 MHz 1H-NMR spectrum showing shift effects of benzyl alcohol; Fig. 5S 600 MHz 1H-NMR spectrum of pogostone; Fig. 6a – bS: 600 MHz 1H-NMR spectra from 3.2 – 3.95 ppm of standard PEO and Clearwood; Fig 7a – iS: individual 60 MHz 1H-NMR spectra of genuine PEOs depicted in [Fig. 2]; Fig. 8S: 60 MHz 1H-NMR spectra of six buchu oils; Fig. 9S: similarity analysis based on NMR data focusing on patchoulol and vetiver (model 3); Fig. 10S: GC-MS fingerprint of PEO; Fig. 11S: biplot PCA based on GC-MS data; Fig. 12S: similarity analysis based on GC-MS data; Fig. 13S: 60 MHz COSY spectrum of standard PEO.

  • Supporting Information