The use of pyrolytic techniques to estimate site specific isotope data of vanillin

Abstract

Two pyrolysis techniques have been investigated for providing site specific isotopic information for vanillin. A Curie Point pyrolyser was used to fragment vanillin samples of known carbon isotopic composition. Hydroxy benzaldehyde, phenol and catechol were produced and identified by gas chromatography mass spectrometry (Py-GC/MS). Their carbon isotopic ratios were measured by gas chromatography combustion isotope ratio mass spectrometry (Py-GC/C-IRMS). The extreme conditions required to produce this fragmentation led to isotopic mixing so that, under the conditions employed, the fragmentation products did not retain isotopic information which could be used for authentication purposes. A second pyrolytic technique generating carbon monoxide under continuous flow conditions for isotope ratio mass spectrometry (Py-CF-IRMS) was used to study vanillin samples. The carbon monoxide gave information on the oxygen isotopes present in the vanillin. In addition, it appears that the carbon–oxygen bond of the parent vanillin molecule is retained so that the carbon isotopic content of oxygen bearing carbons can be measured. Comparison of carbon isotope data measured using this procedure agreed well with the known values of standard materials. The oxygen isotopes also provided useful information on the source discrimination of vanillin samples from fossil fuel and plant sources. Py-CF-IRMS may therefore provide a rapid and convenient technique for authenticating vanillin and other important food flavours.