Oxygen‐18 measurement by continuous flow pyrolysis/isotope ratio mass spectrometry of vegetable oils

Stable isotopes are now increasingly used for the control of the origin or authenticity of food products. Among these techniques, the measurement of the 18O content of organic compounds has rarely been carried out because of technical difficulties in the preparation and measurement of the samples. Recently a few laboratories have worked on the setting up of on-line methods to allow easier access to the information that can be obtained from 18O/16O ratios. In this work, such a technique was developed by modifying an elemental analyser device for carrying out the pyrolysis of organic matter. This device is coupled to an isotope ratio mass spectrometer for 18O determination in the CO resulting from the pyrolysis of the compound to be analysed, with good results. The relationship between the 18O content of various oils and their geographical origins is discussed. © 1998 John Wiley & Sons, Ltd.