to six chemical signatures1
α-CH2’s and alkyls, as shown in Figure 1. The allylic/α-CH2
: carboxylic acids, olefi ns, bis-allylics, allylic/ ’s are defi ned
as the methylene moieties adjacent to either a carbonyl or a vinyl, while bis-allylic resonances are the methylene linkages connecting two vinyl groups. Although the individual components of these fatty acids are not fully resolved at 60 MHz, integrals taken of the defi ned regions can accurately distinguish the various fatty acid forms. Alkyl and α-carbon components are observed in spectra of saturated fatty acids (Figure 1a), whereas the unsaturated fatty acids (Figure 1b) give more complex and informative spectra that integrate according to the degree of saturation and the number of protons for each functional group.
Edible oils will have similar 1 H NMR spectra, save that: 1) the carboxylic acid moiety is replaced by glyceride linkages (–CH2-/-CH-δ 3.82–4.5 ppm) (Figure
2) and 2) the integrations of the chemically distinct spectral resonance ranges refl ect the percent composition of fatty acids for a specifi c edible oil (Table 1). Consequently, 1
H NMR spectroscopy can be used directly to diff erentiate edible oils with diff erent characteristic fatty acid profi les.
Table 1 – Percent composition of extra virgin olive oil and soybean oil
Figure 2 – Stacked 60-MHz 1 H NMR spectra for olive and soybean
oil. (Reproduced with permission from Chemical & Engineering News;
http://www.heterobetainas.uah.es/intranet/REVISTA%20 CHEM&ENG%20NEWS/cen20140602-EUR-dl.pdf)
Edible oils are triglycerides of saturated (e.g., palmitic and stearic) and unsaturated (e.g., oleic, linoleic and α-linolenic acid) fatty acids. Due to their composite nature, interpreting 1
H NMR spectra of oils fi rst requires an understanding of discrete free fatty acid. Free fatty acids can have up Saturated fatty acids
Monounsaturated fatty acids α-Linolenic acid (ω-3) Linoleic acid (ω-6) Oleic acid (ω-9)
EVOO 14 72
<1.5 9–20 0
Soybean oil 15.65 22.78 7
50 24
The Credible Power of Laboratory Product Reviews by Jeanely Hunt, MS, MBA, Web Producer, American Laboratory/Labcompare
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www.labcompare.com/review AMERICAN LABORATORY • 17 • MARCH 2015
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