The Analysis of Flower Fragrances
There is unique period in the growth of a flower, when both the composition and yield of the essential oil is an optimum. For some flowers, there may be a particular time of day when the yield and composition is optimal for harvesting.
Figure 5. Apparatus for Sampling Flower Fragrance for GC Analysis
GC is clearly the ideal analytical technique to determine such optimum conditions. The apparatus used is shown in figure 5. The flower head is covered with a plastic envelope made from a suitably inert material through which the essential oils cannot diffuse (e.g. thin Teflon sheets). When a sample is taken, the neck of the envelope is tied round the stem of the flower to temporarily isolate the flower from the surrounding atmosphere. The envelope is left round the flower for about 10 minutes to ensure equilibrium is established between the flower and the surrounding atmosphere, then the sample is taken. A syringe needle, attached to the adsorption tube is inserted through the envelope and a volume of equilibrated air extracted (ca 100-200 cc) through the adsorption tube. The tube is then capped and stored in a refrigerator. The sample tubes are placed in a padded, thermally insulated box for transportation, preferably while refrigerated at about 2°C.
Typical adsorbents are carbon, silica gel, macro porous polymer adsorbents or a reversed phase. A typical adsorption trap (e.g. Supelpack 20P) would be 6 mm O.D., 7 cm long carrying about 100 mg of macro porous polymer. The sample is usually regenerated by solvent displacement.
One end of the trap (the trap exit) is connected to a syringe containing the displacing solvent and the other end (the end the sample entered) is connected to a hypodermic needle that is made to pierce the septum of a sample vial. The solvent is slowly discharged through the trap by the syringe into the sample vial, desorbing the essentials oils into the solvent as shown in figure 5. The displacing solvent must be absolutely clean and should be passed through a reversed phase column prior to use. A sample of the extract is then injected onto the GC column and the separation developed.
