Supporting characterization thermal analysis techniques

DSC is often used in conjunction with TA to determine if a reaction is endothermic, such as melting, vaporization and sublimation, or exothermic, such as oxidative degradation. It is also used to determine the glass transition temperature of polymers. Liquids and solids can be analyzed by both methods of thermal analysis. The sample size is usually limited to 10-20 mg. Thermal analysis can be used to characterize the physical and chemical properties of a system under conditions that simulate real world applications. It is not simply a sample composition technique. Much of the data interpretation is empirical in nature and more than one thermal method may be required to fully understand the chemical and physical reactions occurring in a sample. Condensation of volatile reaction products on the sample support system of a TA can give rise to anomalous weight changes. 

Large molecules, such as proteins and polymers, do not have the thermal stability to vaporize without decomposing. Desorption ionization sources permit the direct ionization of solids, facilitating the analysis of large molecules. There are several types of desorption sources in which solid samples are adsorbed or placed on a support and then ionized by bombardment with ions or photons. Desorption Cl, one form of desorption ionization, has aheady been described. The important technique of secondary ion mass spectrometry (SIMS) is used for surface analysis as well as characterization of large molecules SIMS is covered in detail in Chapter 14, Section 14.4. Several other important desorption sources are described subsequently. 

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