Principles and Practice of Chromatography - Chromatography Applications > Gas Chromatography Applications > Essential Oils > Page 77


An example of the separation of lime oil employing modern GC techniques is shown in figure 39. The separation was carried out on a SB–5 column, that contained poly(5%diphenyl-95%–dimethylsiloxane) as the stationary phase. Although the diphenyl group will contribute some induced polarizability capability to interact with polar solutes, it is largely a dispersive stationary phase, and thus substances are eluted roughly in order of their boiling points (excepting very polar solutes). The introduction of the diphenyl groups contributes more to phase temperature stability than it does to solute selectivity. The column was 30 m long, 250 mm I.D. carrying a film 0.25 mm thick of stationary phase. Helium was used as the carrier gas at a linear velocity of 25 cm/sec(set at 155˚C).

1. a–Pinene 7. g–Terpinene 13. Geraniol
2. Camphene 8. Terpinolene 14. Neryl Acetate
3. b–Pinene 9. Linalool 15. Geranyl Acetate
4. Myrcene 10. Terpinene–4–ol 16. Caryophyllene
5. p–Cymene 11. a–Terpineol 17.transa–Bergamotene
6. Limonene 12. Neral 18. b–Bisabolen


Courtesy of Supelco Inc.


Figure 39 A Chromatogram of Lime Oil

The column was held isothermally for 8 min. at 75˚C and then programmed up to 200˚C at 4˚c/min. and finally held at 200˚C for 4 min. The sample volume was 0.5 ml which was split at 100:1 ratio allowing about 5 mg to be placed on the column. It is seen from figure 5 that a very good separation is obtained that convincingly confirms the complex nature of the essential oil. In practice, however, the net flavor or odor impact can often be achieved by a relatively simple mixture of synthetic compounds.