Mass spectrometer, double-focusing kinds

Of course, the electron-impact source cannot be used if nonvolatile inorganic samples such as metal alloys or ionic residues are to be analyzed. These substances can be investigated using a different kind of ionization chamber called a spark source, similar to the excitation sources used in emission spectroscopy (Chap. 11). The other parts of the spectrometer can be the same as a general-purpose instrument however, a Mattauch-Herzog double-focusing instrument is preferred (Fig. 16.7 below), because the spark source produces ions with a wide spread of kinetic energies. The entire device is known as a spark-source mass spectrometer (SSMS). 

The calibration of the analyzer from the ions of a known compound allows the measure of the m/z ratios of the detected ions. As mentioned earlier, the ions accelerated from the source always present a certain distribution in kinetic energy at their arrival in the analyzer after collisions or Coulomb repulsions. Due to this distribution in energy, the focaUzation on the collector s slot is not perfect with ions of the same m/z ratio, which means low resolution. It is thus necessary to combine an electrostatic sector to the magnetic sector to achieve high resolution with this kind of system. The double-focusing mass spectrometer is described below. 

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