Thermal desorption (TD) is a readily automated gas extraction technology based on standard gas chromatography parameters. It provides an efficient, high-sensitivity alternative to conventional solvent extraction. The process of TD involves the extraction of volatile or semivolatile organic compounds from a sorbent or material by heating the sample in a flow of inert gas. The extracted analytes are then transferred in the flow of carrier gas to the analyzer [typically a gas chromatograph (GC) or a gas chromatograph/mass spectrometer (GC/MS)] as a small, discreet, and concentrated volume of vapor. The thermal desorber becomes a multipurpose, standalone GC injector. Concentration factors as high as 105 to 106 can be achieved using modern systems with analytes collected from tens to hundreds of liters of air being delivered to the analyzer in as little as 200 µL of gas. Though inherently simple, many factors contribute to the performance and efficiency of the TD process, which determines the ultimate sensitivity and reliability of a TD-based analytical method. These factors include retention efficiency (during sampling/focusing), desorption efficiency, artifacts, band broadening, and analyte/system stability. This overview describes optimization of all of these parameters during the development and validation of TD procedures. Examples of optimum method performance in terms of precision, linearity, and sensitivity are presented. A novel approach to overloading.
