Stable Isotope Analysis.  Professor Wolfram Meier-Augustein

Analytical methods traditionally applied in analytical chemistry or forensic science laboratories establish compound identity as well as a degree of similarity between one compound and another by identifying their constituent building blocks such as functional groups, and by elucidating their chemical structure.  So when looking for example at two samples of pure sugar (sucrose) all of the aforementioned data will correspond and it can be concluded that they are chemically indistinguishable, both are indeed sugar.  However, it can be argued that although two substances in question are chemically indistinguishable, they may not be the same because they do not share the same provenance e.g. may have come from different sources or be of different geographic origin.  In the case of sugar, two major plant sources of directly or indirectly consumed sugar are sugar cane (grown in Brazil, India, South Africa, USA) and sugar beet (grown in Central Europe, USA).  So, in the context of their provenance two spoonfuls of sugar can be completely unrelated and may thus be not the same.

The assertion that two compounds may not be the same because they do not share the same provenance, has already been put forward as defence in criminal case of people standing trial for drug offences such as possession with the intend to supply.  Stable isotope analysis is the method of choice to address the question of provenance and thus to find evidence that proves or disproves this assertion.