Thermal Desorption Instrumentation for Characterization of Odors and Flavors


John J. Manura, Scientific Instrument Services

A wide range of volatile and semi-volatile organics occur in food products that are responsible for their unique odor and flavor. Gas Chromatography is the most commonly system used to analyze these samples using sample preparation techniques such as headspace, thermal desorption, solvent extraction, solid phase micro extraction and supercritical fluid extraction. Each of these techniques has unique advantages and disadvantages when used to analyze various sample matrices.

One of the most sensitive and versatile techniques to analyze food products for volatile organics is the Thermal Desorption Technique with on column cryo-trapping of analytes. Sample preparation methods for the Thermal Desorption Technique include Purge and Trap (P&T) to extract the volatiles from liquid and solid matrix samples and a new technique called Direct Thermal Extraction (DTE) to analyze dry solid matrix samples. The DTE technique requires little sample preparation, is quick as well as quantitative. This paper describes the theory of operation of the thermal desorption and cryo-trapping system, the sample preparation techniques and the proper sample preparation and analysis parameters which can be used to analyze the volatile and semi-volatile organics in a wide range of food and food related type samples. Data presented includes green and black tea sampled via the P&T to study the P&T parameters, thermal desorption parameters and cyro-trapping parameters which can be adjusted to selectively analyze a range of analytes in these samples. Methods are also described for the quantification of analytes in food samples such as the quantification of BHT in gums utilizing the DTE technique.