Improving the recycling technology of waste cooking oils: Chemical fingerprint as tool for non-biodiesel application

NMR Determination of Free Fatty Acids in Vegetable Oils

“…The main drawback of 1 H NMR spectroscopy in oil analysis is related to the small spectral width covered by protons. 13 C NMR spectra as an alternative to 1 H NMR offers some advantages [36]. First, 13 C NMR provides a large number of signals covering a wide range of chemical shifts, which makes However, the 1 H NMR method proposed by Skiera et al presented some limitations in two cases.…”

“…13 C NMR spectra as an alternative to 1 H NMR offers some advantages [36]. First, 13 C NMR provides a large number of signals covering a wide range of chemical shifts, which makes However, the 1 H NMR method proposed by Skiera et al presented some limitations in two cases. For hard fat samples, the AV NMR values were significantly smaller than the AV ones [1].…”

“…13 C NMR spectra as an alternative to 1 H NMR offers some advantages [36]. First, 13 C NMR provides a large number of signals covering a wide range of chemical shifts, which makes the 13 C spectrum very informative. As an example, the 13 C chemical shifts of the main FFA found in WCO (Figure 1) are given in Table 2 [44].…”

“…Using the inverse gated decoupling technique to remove the nuclear Overhauser proton-carbon enhancement, and long pulse delays to ensure the complete relaxation of 13 C nuclei with long spin-lattice relaxation time, it is also possible to acquire a 13 C NMR spectrum under quantitative conditions, as in the case of 1 H NMR [36]. The main drawback is that 13 C NMR experiments typically need long measurement times to obtain a spectrum with proper signal-to-noise ratio. In order to shorten the total experimental time, it is possible to add relaxation reagents (typically chromium (III) acetylacetonate [Cr(acac) 3 ]), which are paramagnetic substances able to significantly reduce the relaxation times of 13 C nuclei without inducing relevant shifts.…”

“…In order to shorten the total experimental time, it is possible to add relaxation reagents (typically chromium (III) acetylacetonate [Cr(acac) 3 ]), which are paramagnetic substances able to significantly reduce the relaxation times of 13 C nuclei without inducing relevant shifts. In the field of lipid chemistry and technology, high resolution 13 C NMR has established itself as a versatile technique to determine the composition of mixtures of fatty acids and lipid molecules, control the purity and reveal adulteration, authenticate the geographical origin and assess quality, quantitatively determine fatty acid profiles, evaluate oxidation products, analyse the phenolic fraction and determinate iodine value [2,37,38,52].…”