Although enantiomeric distribution provides a useful parameter for the evaluation of authenticity and quality of the oils, there are a lot of non-chiral but sensorily important essential oil compounds. Recently, the determination of the natural abundance of stable isotope by means of stable isotope ratio mass spectrometry (IRMS) has been demonstrated to be useful in the origin assessment and authenticity control of flavours and fragrances. Conventional IRMS requires relatively large sample volume in a purified gaseous form. Recently, an 'on-line' capillary GC-IRMS system has been developed, which combines the high purification effect of GC with the high precision of IRMS. A schematic of this system is shown in Figure 12.6. The substances eluting from the GC column are converted into C02 in a combustion oven and then directly analysed in the isotope mass spectrometer, adjusted for the simultaneous recording of masses 44 (12C1602); 45 (13Cl602, 12C160170) and 46 (12C160180) in the nanomole range and with high precision (<0.3%o). Isotope ratios are calculated relative to standard values (¿-values, given as %o), where ¿-values is the relative difference in the isotope ratio of the sample to that of the international standard PDB (belemnitella Americana from the crustaceous Pedee formation, South California, USA).
Was this article helpful?