Gas Chromatography - Applications > The Head space Analysis of Tobacco > Page 68

The Headspace Analysis of Tobacco

Tobacco is a herbaceous plant, the leaves of which are harvested, cured and suitably prepared for smoking, as cigars or cigarettes, or alternatively, chewing or taken as snuff. Its main component, nicotine is habit forming and other compounds produced by pyrolysis during smoking are carcinogenic and can cause a number of other health problems. Tobacco is an extremely valuable export in the United States despite the health concern, and its quality is carefully monitored. Tobacco can be flue cured, air cured, fire cured or sun cured, but the quality of the product can often be monitored by analyzing the vapors in the headspace above the tobacco. The headspace over tobacco can be sampled and analyzed using a Solid Phase Micro Extraction (SPME) technique. The apparatus used for SPME is shown in figure 44.

The extraction apparatus consists of a length of fused silica fiber, coated with a suitable polymeric adsorbent, which is attached to the steel plunger contained in a protective holder. The steps that are taken to sample a vapor using the apparatus are represented in figure 44. The sample is placed in a small headspace vial and allowed to come to equilibrium with the air (1). The needle of the syringe containing the fiber is the made to piece the cap, and the plunger pressed to expose the fiber to the headspace vapor. The fiber is left in contact with air above the sample for periods that can range from 3 to 60 minutes, depending on the nature of the sample (2). The fiber is then removed from the vials (3) and then passed through the septum of the injection system of the gas chromatograph into the region surrounded by a heater (4). The plunger is again depressed and the fiber, now protruding into the heater is rapidly heated to desorb the sample onto the GC column. It is advisable to arrange for the column is kept cool so the components concentrate on the front of the column.