Gas Chromatography - Applications > Food and Beverage Products > Page 74

A headspace sample was taken, employing the method previously described using 0.5 g of pine leaves contained in a 7 ml vial. The solid state extraction procedure employed a glass fiber coated with a polysiloxane film which was exposed to the sample vapor at 40˚C for 20 minutes. Using the special applicator, the fiber was withdrawn from the sample vial and placed in a unique capillary column sample device. The fiber was then heated to 250˚C for one minute and the vapors passed onto the column using a split injector with a 100:1 split. The column used was 30 m long 0.25 mm I.D. and carried a film of b-DEX 0.25 mm thick and was programmed from 40˚C to 220˚C at 4˚C/min. Helium was used as the carrier gas at a velocity of 35 cm/s. It is seen that the sample is broadly separated into two groups, the monoterpenes and the sesquiterpenes. The enantiomers of a-pinene and camphene are cleanly separated. As these compounds contain no polar groups, the chiral selectivity must be based entirely on differential dispersive interactions with the derivatized cyclodextrin.

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The columns were 30 m long, 0.25 mm I.D., carrying a film of stationary phase 0.25 mm thick of b-DEX™. The column was programmed from 40˚C to 220˚C at 4˚C/min. The helium flow velocity was 35 cm/s.

Figure 48 Chromatogram of the Essential Oil From White Pine Leaves

It should be noted that whereas the (–)-a-pinene is the first eluted enantiomer of a-pinene it is the (+)-camphene that is the first eluted of the camphene enantiomers. This tends to indicate that there is no rational procedure for predicting the order of elution of an enantiomeric pair.