Flavor authenticity studies by isotope ratio mass spectrometry : Perspectives and limits

In recent years authenticity assessment of flavor substances has gained increased importance by using multi-element isotope ratio mass spectrometry (IRMS). Whereas 13 C/ 12 C ratio determinations have already been performed previously by coupled gas chromatography (GC) in the combustion (C) mode, the technical prerequisites for GC-pyrolysis (P)-IRMS were made available only recently, Thus, the additional information about the 2 H/ 1 H and 18 O/ 16 O ratios of industrially attractive flavor compounds opened the way to multi-element approaches. From the current studies conclusions can be drawn concerning (i) general and (ii) element-specific requirements for GC-C/P-IRMS measurements. They comprise for (i) the availability of authentic reference material, statistically relevant sample numbers, the exclusion ofisotope discrimination in the course of sample preparation and chromatographic steps, as well as continuous checks of system stability using certified standards. As to (ii), GC-C-IRMS measurements of 13 C/ 12 C ratios are routinely performed; the GC-P-IRMS determination of 2 H/ 1 H ratios is a highly promising technique provided that the dynamic linearity is checked carefully and, depending on the structure of the target molecule potential isotope exchange is excluded. GC-P-IRMS measurements of 18 O/ 16 O ratios still suffer from the empirical pyrolysis technique and the need to use tertiary standardization. In addition, similarly to 2 H/ 1 H determinations, check of dynamic linearity and potential isotope exchange is required. Considering these requirements, GC-P-IRMS is an additional helpful tool in the authenticity assessment, in particular, as predictions about the global δ 18 O VSMOW and δ 2 H VSMOW values of natural compounds on the basis of their biogenesis are increasingly available.