. The head space 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 head space 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 head space 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 procedure as outlined by Supelco Inc. is as follows. 1 g of tobacco (12% moisture) was placed in a 20 ml head space vial and 3.0 ml of 3M potassium chloride solution added. The fiber was coated with polydimethyl siloxane (a highly dispersive adsorbent) as a 100 mm film. The vial was heated to 95˚C and the fiber was left in contact with the head space for 30 min. The sample was then desorbed from the fiber for one minute at 250˚C.   Courtesy of Supelco Inc.   Figure 45 A Chromatogram of Tobacco Head Space   The separation was carried out on a column 30 m long, 250 mm I.D. carrying a 0.25 mm thick film of 5% phenylmethylsiloxane. The stationary phase was predominantly dispersive with a slight capability of polar interactions with strong polarizing solute groups by the

nbsp; Courtesy of Supelco Inc.   Figure 44. The Solid Phase Micro Extraction Apparatus   When desorption is complete (a few seconds) the column can then be appropriately temperature programmed to separated the components of the sample. A chromatogram of the head space sample taken over tobacco is shown in figure 45

A head space 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 Using the special applicator, the fiber was withdrawn from the sample vial and placed in a unique capillary column sample device.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

penalties. In addition, the condition of the food is also of great concern to the food chemist, who will look for those trace materials that have been established to indicate the onset of bacterial action, aging, rancidity or decomposition. In addition, tests that identify the area or country in which the food was processed or grown may also be needed. The source of many plants (herbs and spices) can often be identified from the peak pattern of the chromatograms obtained directly from head space analysis. Similarly, unique qualitative and quantitative patterns from a GC analysis will often help identify the source of many alcoholic beverages. Unfortunately, food analysis involves the separation and identification of very complex mixtures and the difficulties are compounded by the fact that the components are present at very low concentrations. Thus, gas chromatography is the ideal (if not only) technique that can be used successfully in food and beverage