The enantiomeric distribution of volatile components of citrus oils provides a useful parameter for the evaluation of genuineness and quality of the oils. Chiral gas chromatography, using modifi ed cyclodextrins, as a stationary phases, is the most common technique for the determination of the enantiomeric distribution of the volatile components.
The volatile fraction of citrus oils is usually a very complex matrix. Therefore the direct gas chromatographic determination of its components, though sometimes possible, is usually diffi cult. In fact, it requires particular attention for the choice of the most appropriate experimental condition and stationary phases, in order to avoid co-elution of enantiomers with other components. Coupled systems of liquid chromatography and gas chroma tography (LCGC), and multidimensional gas chromatographic systems (MDGC), permits the pre-fraction ation of the samples and the further chiral analysis of the components of interest. These techniques avoid possible peak overlaps. The LC-GC methods have rarely been used, while the MDGC systems are more commonly employed.
The early multidimensional GC systems were based on Dean’s principle, while systems working with mechanical valves, proposed earlier, were not considered reliable, because the valves available at the time did not have adequate thermal stability. In addition, Memory effects were likely to occur. Technological progress of valve design rendered miniaturized connectors available for the assembly of multidimentional GC systems, eliminating upswept volumes. These mechanical valves are stable at high temperatures and can be used to set up multidimensional GC systems without any drawbacks. They are easier to operate than those based on Dean’s principle.