High Quality Content by WIKIPEDIA articles! Evolved gas analysis (EGA) 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.