High-resolution1H and2H NMR spectroscopy of pure essential fatty acids for plants and animals

Abstract

High-resolution 1H and 2H NMR spectroscopy were used to study the most important saturated (C14:0, C16:0, C18:0), monounsaturated (C16:1n-7, C18:1n-7, C18:1n-9, C20:1n-9, C22:1n-9) and polyunsaturated [C18:3n-3, C20:5n-3 (EPA), C22:6n-3 (DHA)] fatty acids which may be found in fish lipids, in order to prepare the tools for a subsequent study of the recognition of the origin of fish oils by isotopic analysis. The interpretation of the 1H and 2H NMR spectra of the different acids is reported. Additionally, the overall D/H and the 13C/12C isotope ratios are given. The overall D/H ratio ranges from 114.0 to 137.2 ppm/V.SMOW (V.SMOW=water standard) and the 13C/12C ratio from -23.5 to -33.2‰. From the 2H NMR spectra, an investigation of the internal deuterium distribution in the saturated and mono- and polyunsaturated fatty acids was made. The deuterium distribution can be given for nearly all the chemical sites, except for the different double bonds, in EPA and DHA. The precision of the measurements was of the order of 0.5–4% depending on the nature of the cluster considered. © 1997 John Wiley & Sons, Ltd.