Fatty acids isotope ratios

Figure 14.22 Hydrogen isotope ratios of CJ6 oand Cis.-o fatty acids in modern horse milk and adipose fat, both from Kazakhstan (a), displaying seasonal influences [ellipses are 68 % (la) confidence intervals], compared (b) with 8 D values recorded for fatty acids from Eneolithic cooking pot sherds from Botai residues assigned as equine fats based on 813C analysis. Confidence ellipses are la and correspond to the modern reference equine fat values (Outram et al. 2009)...

Hammer, B. T., Fogel, M. L. and Hoering, T. C. (1998) Stable carbon isotope ratios of fatty acids in seagrass and redhead ducks. Chemical Geology 152, 29 41. 

Metges, C. C., Kempe, K. and Wolfram, G. (1994) Enrichment of selected serum fatty acids after a small oral dosage of (1 C 13)triolein and (8 C 13)triolein in human volunteers analyzed hy gas chromatography combustion isotope ratio mass spectrometry. Biological Mass Spectrometry 23,295 301. 

Scrimgeour, C. M., Begley, I. S. and Thomason, M. L. (1999) Measurement of deuterium incorporation into fatty acids by gas chromatography/isotope ratio mass spectrometry. Rapid Communications in Mass Spectrometry 13, 271. 

Interpretation/results A GC-isotope ratio MS technique is used on known animal fats and the ancient samples. (In this technique, each peak eluting from the GC is combusted to C02 and its 12C-13C ratio is measured by a mass spectrometer [7].) The 13C ratio of the C-16 0 and C-18 0 fatty acids are plotted. The knowns are concentrated in specific areas on the plot, shown as ellipses in Fig. 21.16. The position of the cream sample points on this pattern recognition plot indicates that the fatty portion of the cream is from ruminant adipose tissue. 

If the fatty acid composition is within the accepted range for the oil, then other analyses should be carried out. Those used will vary with the oil. If the oil being examined is maize, then the carbon isotope ratio should be examined. This is carried out by burning the oil and determining the ratio of 13C to 12C. From this it is possible to detect 10% or above of an oil other than maize (Rossell, 1994). 

Kelly, S., Parker, I., Sharman, M., Dennis, J. and Goodall, I. (1997) Assessing the authenticity of single seed oils using fatty acid stable carbon isotope ratios. Food Chem., 59, 181-186. 

Rossell, J.B. (1994) Stable isotope ratios in establishing maize oil purity. Fat Sci. Technoi, 96, 304-208. Royer, A., Gerard, C., Naulet, N., Lees, M. and Martin, G.J. (1999a) Stable isotope characterisation of olive oils. 1. Compositional and carbon-13 profiles of fatty acids. J. Am. Oil Chem. Soc., 76, 357-363. 

Technology has now advanced to the point that one can obtain stable 5 - C and d T) ratios of individual fatty acids. Because different species isotopically fractionate fatty acids in different ways and to different degrees, these ratios can be used to identify further the fats from different sources (Fig. 4.31). One such study examined... 

Fig. 6.14 A plot of 5 C isotope ratios for two fatty acids (C16 0, Cl8 0) that are different for marine and most terrestrial animals. The circles are values from modern animals the vertical and horizontal lines show the range of variation in the values. The open squares are potsherds from places where hunters lived 6,500 years ago the black squares are potsherds from places where farmers lived 5,500 years ago in northern Europe. The hunters pottery had more marine contents the farmers pottery had more terrestrial contents, perhaps including milk...

Additionally, significant variations of the standard deviation values were observed with respect to the individual compounds. The precision of S13C-values of n-alkanes, 2,2,4,4,6,8,8-heptamethylnonane, fatty acid methyl esters, phthalates and musk fragrances was generally acceptable down to amounts of approx. 5 ng with standard deviation values below 1.0 %o. On the contrary, already at the 25ng- and lOng-levels the stable carbon isotope ratios of the chlorinated compounds (CI5- and Cf,-benzene, Clfi-butadiene) as well as of tetrabutyl tin were measured with high standard deviations between 0.8 %o and 3.2 %o. 

Much effort has also been employed on developing new authentication methods for olive oils. The method of determination of hydrogen isotope ratios, D/H, at specific sites in fatty acids has been used to characterize 200 oils in terms of country, region, and year of production.198... 

Abraham WR, Hesse C, Pelz O (1998) Ratios of carbon isotopes in microbial lipids as an indicator of substrate usage. Appl Environ Microbiol 64 4202-4209 Abrajano Jr. TA, Murphy DE, Fang J, Comet P, Brooks JM (1994) ratios in individual fatty acids... 

Stable carbon isotopes data—The data from stable isotope and radiocarbon measurements are summarized in Table 1. Analytical precision is 0.l%o for C. Stable carbon isotope ratios of the different fractions span from — 20.14 to — 27.82%o with the unextracted and extracted sediments exhibiting values, as expected, in the midrange around — 22%o (Fig. 1). The only exception is the fatty acid fraction which is anomalously depleted in Stable carbon isotope numbers of the different compound classes from the SMB samples, in general, suggest a mixing of terrestrial and marine components with humic and fidvic acids implying major contribution from marine sources (Sweeney and Kaplan, 1980 Stuermer et al., 1978). 

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