Head space analysis Head space analysis is basically a technique where the vapors in the gas above, and in equilibrium with a solid or liquid is sampled, as opposed to sampling, solely, the solid or the liquid themselves. The advantage of this approach is that gas chromatography can be used as the analytical technique, as opposed to liquid chromatography, thus providing four to five orders of magnitude greater sensitivity. The procedure involves the extraction of a volume of the equilibrium gas over the sample (usually about 10 ml) by a syringe through a vial containing a bed of an appropriate absorbent. The vial is the placed in line with a gas chromatography column, the vial heated and the vaporized sample swept on the column and the components separated. This technique has been used to identify spoiled food, fragrances from botanical material, the determination of plasticizers in plastics and for forensic samples involving arson.
Author: RPW Scott
Book:Gas Chromatography
Section:GC Applications Lime-Oil
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 head space above the tobacco. 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
Author: RPW Scott
Book:Gas Chromatography
Section:GC Applications Food-and-Beverage-Products
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 assays and tests. The potential carcinogenity of the aromatic hydrocarbons make their separation and analysis extremely important in environmental testing. However, the aromatics can pose
