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EGA – Evolved Gas Analysis is a method used to study the gas evolved from a heated sample that undergoes decomposition or desorption. It is possible to detect which gas is evolved using evolved gas detection (EGD). EGD is often performed by coupling EGA with mass spectrometry, Fourier transform spectroscopy, gas chromatography, or Optical In-Situ Evolved Gas Analysis.

By coupling the thermal analysis instrument, e. g. TGA (Thermogravimetry) or DSC (Differential scanning calorimetry), with a fast Quadrupole Mass Spectrometer (QMS) the detection of gas separation and identification of the separated components are possible in exact time correlation with the other thermal analysis signals. DSC/TGA-QMS or TGA-QMS yields information on the composition (mass numbers of elements and molecules) of the evolved gases. It allows fast and easy interpretation of atomic/inorganic vapors and standard gases like H2, H2O, CO2, etc. Fragmentation, interpretation of organic molecules is sometimes difficult.

The combination with an FTIR (Fourier Transform Infrared Spectrometer) has become popular, especially in the polymer producing, chemical and pharmaceutical industry.  DSC/TGA-FTIR or TGA-FTIR yields information on the composition (absorption bands) of the evolved gases (bonding conditions). The advantage is an easy interpretation (spectra data bases) of organic vapors without fragmentation. Symmetrical molecules can not be detected.