C and H stable isotope ratio analysis using solid-phase microextraction and gas chromatography-isotope ratio mass spectrometry for vanillin authentication.

It is possible to distinguish precious vanillin from Vanilla species (planifolia or tahitensis) from much less expensive synthetic and nature-identical vanillin on the basis of the stable isotope ratios of H and C (2H/1H, 13C/12C). Analysis is usually performed using GC-IRMS (Gas Chromatography - Isotope Ratio Mass Spectrometry) after solvent extraction of vanillin from the sample. Recently, head-space solid-phase microextraction (HS-SPME) has been proposed as an alternative for determining 13C/12C. The aim of this study was to develop a method to analyse 2H/1H in vanillin using SPME-GC-IRMS for the first time, by testing different operating conditions and comparing the results with those obtained after solvent extraction. The ultimate scope was to develop a quick, robust and effective method to measure 2H/1H and 13C/12C in vanillin to assess the authenticity of labelling. Almost 50 authentic samples from vanilla pods, nature-identical (ex) and synthetic vanillin and 4 commercial food products were taken into account. All the samples were subjected to HS-SPME-GC-IRMS analysis and most of them to GC-IRMS analysis after solvent extraction of vanillin. The SPME method developed for 2H/1H analysis guarantees the absence of isotopic fractionation, repeatability and reproducibility standard deviation of below 7‰ and savings in terms of time (from 30 to 5 min) and solvent. HS-SPME GC-IRMS analysis of δ2H and δ13C can be proposed as a rapid and robust method to discriminate different types of vanillin and assess the authenticity of natural vanillin, also contained in food matrices.