Authentication of Mustard Oils by Combined Stable Isotope Analysis (SNIF-NMR and IRMS)

Abstract

Allyl isothiocyanate is the major component of the mustard oil. This molecule can be synthesized at a much lower price than its cost when extracted from mustard seeds. Adulteration of natural mustard oil by adding synthetic allyl isothiocyanate is therefore very profitable. In order to detect such a fraud, a new analytical approach has been developed using both SNIF-NMR (site-specific natural isotope fractionation studied by nuclear magnetic resonance) and IRMS (isotopic ratio mass spectrometry). This approach enables an unambiguous distinction between natural and synthetic allyl isothiocyanate. It also makes it possible to identify the geographical origin of natural mustard oils. The principle of the interpretation is based on a multivariate analysis of the isotopic parameters of allyl isothiocyanate, (D/H)i, δ13C, δ15N, and δ34S, which provide largely independent information. The discriminating performances of the different isotopes are discussed. Keywords: Allyl isothiocyanate; mustard oil; SNIF-NMR; 1...