Hydrogen stable isotope ratio analysis

A reliable authenticity assessment is concluded from the simultaneous consideration of multielement IRMS and enantioselective analysis. The differences of the stable isotope ratios of linalool and linalyl acetate are depicted as a three-dimensional plot of A values (d values of linalool minus d values of linalyl acetate for oxygen, hydrogen and carbon) (Fig. 17.15). This plot shows that the commercial samples S1-S5 are different from all the other samples investigated. Linalool and linalyl acetate of S1-S5 definitely are not genuine lavender oil compounds. 

The isotopic distribution found in natural F F compounds serves as a signature that analysts can use to differentiate natural compounds from synthetic analogs. The metabolic pathways that plants use to create carbon compounds discriminate between C and C. The C/ C ratio of the carbon dioxide the plant uses as a reactant differs from the C/ C ratio of the compounds the plant produces. Stable carbon isotope ratio analysis (SIRA) measures the C/ C ratio and can authenticate the natural or synthetic origins of some F F materials. SIRA applied to isotopes of hydrogen, or D and H can also serve to authenticate natural F F materials. When combined with GC the on-line or D/ H SIRA analysis can authenticate each component in a complex mixture such as a cinnamon bark oil (19). 

Table 6.13 Site-specific stable hydrogen isotope analysis of linalylacetate by SNIF-NMR. Adapted from [230] with kind permission. Copyright [1992] American Chemical Society. The overall D/H- and ( C/ C)-isotope ratios are determined by combustion and IRMS. S C-values are expressed in [%c[ V5. V-PDB, the overall D/H- and the site-specific D/H-ratios in parts per million [ppm], position indication see Fig. 6.22 (D/H) is the methyl group of the acetyl residue in this case...

I60 and deuterium/hydrogen ratios in sedimentary organic matter could be of advantage to paleolimnological studies concerned with the reconstruction of paleoclimate. However, there are considerable practical difficulties in the analysis of these stable isotopes and few laboratories currently have the required level of analytical skills. 

Paint and Varnish Finnigan Mat [86] analyzed the carbon and nitrogen isotope values in paint and varnish samples using an EA-IRMS. Differentiation of these samples was achieved based on a combination of the isotope values of the two elements. Farmer et al. [87] provide an overview of research conducted to determine the stable isotope composition of 51 white architectural paints. Carbon, oxygen and hydrogen isotope values were measured and likehhood ratio analysis applied to the data. While samples originating from different sources were differentiated, a false-positive rate of 2% was observed. 

This topic, compartmental analysis, is not covered in this volume and the reader is referred to specialized literature (Zierler, 1981, and references therein). Stable isotopes of different weights can also be used for this purpose in conjunction with mass spectrometry. Deuteriiun in particular, because of its large ratio to the atomic weight of hydrogen, is a suitable tracer. 

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