Other techniques used in MS and their relation to pyrolysis

Besides El, Cl, FI or FD techniques for generating ions in the mass spectrometer, some other ionization techniques have been reported. One such technique is metastable atom bombardment (MAB), which Is based on Penning ionization. In MAB a metastable ion beam generated outside the ion volume is used to bombard the sample. The energy available for ionization is discrete (quantified) and can be fixed by the choice of the rare gas used in the atom gun (He, Ne, Ar, Kr, Xe). This energy ranges from 8 to 20 eV. 

Use of an appropriate rare gas allows the control of the internal energy transferred to the ions formed, and fragmentation can be diminished or made more significant. By eliminating extensive fragmentation during ion formation, MAB can be used in connection with Py-MS. MAB can also be used in combination with MS/MS analysis of the pyrolysates. 

Another MS technique used in connection to pyrolysis is MIMS (membrane introduction mass spectrometry). MIMS is in fact a special inlet for the mass spectrometer, where a membrane (usually silicone, non-polar) lets only certain molecule types enter the Ionization chamber of the MS. This allows, for example, direct analysis of certain volatile organic compounds from air. The system makes possible the coupling of atmospheric pyrolysis to a mass spectrometer [61a] allowing direct sampling of the pyrolysate. Other parts of the mass spectrometer do not need to be changed when using MIMS. 

The theory of a simple thermoionic process [64] has been adapted to find the number of desorbed particles from a given surface covered with an organic layer that does not absorb the laser energy. However, the heat flux in the substrate, which absorbs the energy, heats the sample to the same temperature as the substrate. This number N is given by relation  

By modifying the laser wavelength (and intensity) or using a second laser, a photoionization process may be included (LPI) to generate ions from the analyte that will be further separated and detected in the mass spectrometer. When the ion formation from the plume of the first laser is low, some other secondary ionization techniques such as Cl can also be used. 

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Other techniques used in MS and their relation to pyrolysis. 

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