Evolved Gas Analysis (EGA) is an effective hyphenated analytical technique that is used to describe the gaseous products produced by a sample through a controlled thermal treatment. During the heating of a material, it may pass through different processes like dehydration, decomposition, oxidation, or desorption of solvents, and each process releases a given volatile compound. EGA does not merely sense a change in mass or a heat flow; it directly identifies the chemical nature of gases that caused such occurrences.
Fundamental Principles and Working Mechanism
The main idea of EGA consists of the fact that the sample is heat-stimulated under controlled conditions, and then some gases are released and analyzed. The sample is put into a furnace, and a certain temperature ramp (e.g., 10°C/min) is brought to it under a certain atmosphere (inert, oxidizing, etc.). Volatile components evolved as the temperature rose. To avoid condensation, the stream of gas that contains these effluents is constantly moved out of the thermal analyzer into the gas detector through a heated transfer line.
Key Applications
Polymer science is applied in the identification of plasticizers, stabilizers, and monomers, and the study of the mechanisms of decomposition of complex polymer blends and composites. In the pharmaceutical sector, EGA plays a vital role in the measurement of the remaining solvents, water, and the thermal degradation mechanisms of active pharmaceutical substances (API) and excipients. In catalysis studies, it is used to characterize catalyst precursors, perform coke formation and coke combustion on catalyst surfaces, and to characterize active sites by temperature-programmed desorption (TPD) or reduction (TPR).
Advantages
The main strength of evolved gas analysis lies in its incomparable capability of offering first-hand chemical understanding of the thermal processes, turning ambiguous thermal occurrences into known chemical reactions. EGA is used to directly relate a mass loss step or a thermal event to the gas or gases that are being evolved by hyphenating a thermal analyzer, such as a TGA, with a gas analyzer, such as an MS or FTIR. This removes the speculation that may be involved in interpreting isolated TGA or DSC data, enabling scientists to unambiguously separate processes such as dehydration, degradation of the various components, solvent loss, and combustion.
Limitations
Evolved gas analysis, although having strong analytical potential, has a number of technical limitations. The interface and transfer line between the thermal analyzer and the gas detector are a major challenge. This line should be kept at a high enough temperature to avoid condensation of effluents that are semi-volatile or high-molecular-weight, which can cause blockages and signal loss.
Conclusion
Evolved gas analysis is an innovative analytical method that extends thermal analysis and analytical chemistry. EGA is a combination of the quantitative mass loss data obtained in a TGA with the chemical identification capability of MS or FTIR to give a detailed overview of the volatile products that are produced during thermal treatment. This power is essential in explaining the decomposition processes, product quality and safety, as well as the innovation in designing materials.
