Gas Chromatography - Applications > Lime Oil > Page 67
The use of modern GC techniques to separate a sample of lime oil is shown in figure 43. A SB–5 column, that contained poly(5%diphenyl-95%–dimethylsiloxane) as the stationary phase was used to carry out the separation. It is largely a dispersive stationary phase, although the diphenyl group will contribute some induced polarizability capability to interact with polar solutes. As a consequence substances are eluted roughly in order of their boiling points (excepting very polar solutes).
|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. trans–a–Bergamotene|
|6. Limonene||12. Neral||18. b–Bisabolen|
Courtesy of Supelco Inc.
Figure 43 A Chromatogram of Lime Oil
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). 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 43 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.