Natural products, isotope ratios

Authenticity evaluation has recently received increased attention in a number of industries. The complex mixtures involved often require very high resolution analyses and, in the case of determining the authenticity of natural products, very accurate determination of enantiomeric purity. Juchelka et al. have described a method for the authenticity determination of natural products which uses a combination of enantioselective multidimensional gas chromatography with isotope ratio mass spectrometry (28). In isotope ratio mass spectrometry, combustion analysis is combined with mass spectrometry, and the ratio of the analyte is measured versus a... 

Isotopic analysis of amino acids containing natural abundance levels of 15N was performed by derivatization, GC separation, on-line combustion and direct analysis of the combustion products by isotope-ratio MS. The N2 gas showed RSD better than 0.1%c for samples larger than 400 pmol and better than 0.5%o for samples larger than 25 pmol. After on-column injection of 2 nmol of each amino acid and delivery of 20% of the combustion products to the mass spectrometer, accuracy was 0.04%e and RSD 0.23%o19. 

Kumar N, Anderson RF, Mortlock RA, Froelich PN, Kubik P, Dittrich-Hannen B, Suter M (1995) Increased biological productivity and export production in the glacial southern ocean. Nature 378 675-680 Malinovsky D, Stenberg A, Rodushkin I, Andren H, Ingri J, Ohlander B, Baxter DC (2003) Performance of high resolution MC-ICP-MS for Fe isotope ratio measurements in sedimentary geologic materials. J Anal... 

In addition to sensory and physical properties, the content of certain typical components is determined. Problems concerning the natural, botanical, and geographical origins of these products are also solved by using modern chromatographic methods such as enantiomer separations [843-843c], and spectroscopic analytical techniques such as isotope ratio mass spectrometry (IRMS) [844-844b],... 

Synthetic vanillin is a major intermediate in the production of various chemicals, including medicines and herbicides. Because of the large difference in price between vanillin from a natural origin and synthetic vanillin, counterfeiting is not uncommon. As natural and synthetic vanillin are chemically identical, isotope ratios of hydrogen (D/ff) and carbon ( C/ C) isotopes are used to... 

There are limitations beyond the difficulty of measuring small peaks The 13C/12C ratio differs with the source of the compound—synthetic compared with a natural source. A natural product from different organisms or regions may show differences. Furthermore, isotope peaks may be more intense than the calculated value because of ion-molecule interactions that vary with the sample concentration or with the class of compound involved. For example ... 

With increasing thermal stress, H/C and S/C elemental ratios of kerogens and S, C and H isotope ratios of pyrolysis products show systematic maturation trends. S isotope fractionation between solid, liquid and gaseous pyrolysates falls within a narrow range of about 2 per mil and mimics the variation observed in natural samples. These results confirm the utility of S isotopes towards source rock-oil correlations in sedimentary basins. 

Naturally-occurring products are being examined also for different isotopic ratios of carbon. Water from various sources are known to vary in density up to ten parts per million. These differences are due chiefly to the different ratios of oxygen isotopes, and in part to the different deuterium ratios. 

Yoshida, N. (1988). 15N-depleted N20 as a product of nitrification. Nature. 335, 528-529. Yoshinari, T., Altabet, M. A., Naqvi, S. W. A., codispoti, L., Jayakumar, A., Kuhland, M., and Devol, A. (1997). Nitrogen and oxygen isotope composition of N2O from suboxic waters of the eastern tropical North Pacific and the Arabian Sea- measurement by continuous-flow isotope-ratio monitoring. Mar. Chem. 56(3-4), 253-264. 

Calvert, S. E., Nielsen, B., and Fontugne, M. R. (1992). Evidence from nitrogen isotope ratios for enhanced productivity during formation of eastern Mediterranean sapropels. Nature 359(6392), 223-225. 

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