Analytic validation of isotopic analysis of vanilla products.

Extraction and purification steps were statistically studied using gas chromatography coupled on-line with isotope ratio mass spectrometry (GC-IRMS). First, the C-13 isotope deviation of vanillin was determined for 10 extracts prepared from the same vanille bean sample. The calculated confidence interval (0.11) with a 95% confidence level was less than the dubiousness given by the constructor (+/- 0.3 parts per thousand), so no significative discrimination occurs during this step. Second, for 36 samples of vanilla beans and flavors, the C-13 isotopic deviation was measured, on one hand, directly on the extract prepared from each sample, on the other hand, after liquid chromatography purification. Two statistical studies were carried out. One used the NF X 06066 standard (comparison of paired observations). The second is based on the protocol for evaluation of an alternative quantitative method against a reference method described in the NF V 03110 standard. With a 5% error of first kind, the two statistical treatments showed that the two methods give similar results: no carbon isotopic discrimination occurs during vanillin purification if using well defined processes and systematic controls.