By Setaram Solutions for STA / TGA - EGA coupling EVOLVED GAS ANALYSIS Thermogravimetry (TG) or Thermogravimetric Analysis (TGA) measure the mass loss or gain of a sample of material as a function of time or temperature when it is heated or cooled under a certain temperature profile. Simultaneous thermal analysis (TG-DTA or TG-DSC) additionally allows qualifying or quantifying the corresponding heat effects. But these two methods do not allow for the proper identification of the products of the studied reactions or decompositions and for the determination of their mechanism. The contribution of hyphenated techniques, also known as Evolved Gas Analysis (EGA) in the field of thermogravimetry is well established, with a large number of applications. They have proved particularly interesting for the investigation of the chemistry of a reaction or thermal decomposition owing to the identification of the evolved species. MASS SPECTROMETRY TGA-MS Coupling by heated capillary tube The gases evolved by the sample are collected in the TGA furnace close to the crucible. They are quickly (approx. 100 ms) transferred to the ion source of the Mass Spectrometer thanks to the pressure difference between the TGA furnace (approx. 1 bar) and MS (approx. 10-7 mbar). The gases are not exposed to a temperature lower than 300 °C during the transfer. The ionized molecules and fragments are then separated according to their m/z ratio and detected. The intensity of one or more selected characteristic m/z can be monitored and superimposed to the mass variation signal. Full spectra can also be acquired frequently over the duration of the TGA experiment. Mass spectrometers with amu ranges up to 300 can be employed. Two-steps decarbonatation of a dolomite (CaMg) (CO3)2 sample CO2 evolution is identified thanks to the ion current intensity of m/z 44, 6 and 12 signals

Sampling orifice Skimming cone orifice Skimming cone Primary pump Formation of Mach disk Beam of molecules at supersonic speed To the ionic source of the MS COMBINED GAS CHROMATOGRAPHY AND MASS SPECTROMETRY TGA-GC/MS Supersonic System Here the evolved gases are accelerated by a two steps pressure drop system. Their speed overcoming the speed of sound, they are instantaneously transferred to the ion source, avoiding any condensation or recombination during their route. Heavy, high boiling point molecules like metal vapors or polyaromatic compounds can thus be detected. Mass spectrometers with...

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