Mass spectrometer general scheme

As mentioned earlier, fragmentation in a mass spectrometer generally follows known reaction schemes. We will use this knowledge during calculation of a match value for structure candidate M with respect to experimental mass spectrum I. The calculation is similar to that for molecular formula candidates. However, in the case of structural formulas we can considerably restrict the set of possible fragment molecular formulas jSj. We will consider only such molecular formulas for which fragments exist that are derived from M by successive ionization and fragmentation reactions. To simulate these we go back to the previous work in Section 2.3. 

Fig. 1.1. General scheme of a mass spectrometer. Often, several types of sample inlets are attached to the ion source housing. Transfer of the sample from atmospheric pressure to the high vacuum of the ion source and mass analyzer is accomplished by use of a vacuum lock (Chap. 5.3).

We have been investigating a similar scheme set up on the basis of SSMS-determined impurities presumably the classification might be even more definitive since more trace elements can be estimated. The mass spectrometer data for 44 type I ores is presented in Figures 3 and 4 for comparison the NAA data for 214 type I ores is shown in Figure 5. In general, both the location of the peaks and the width of the distributions for corresponding elements are quite similar. 

The flows are switched using a four-port valve (1) with pneumatic or electric drive. The switching time should be minimal to avoid noticeable flow disturbance and cannot exceed the gas response time of the mass spectrometer. This response time is generally equal to 0.1-0.2 s. Another four-port valve (2) commutes the flows analyzed by mass spectrometry (MS), but is not necessary in the scheme shown. 

In general, to improve the mass resolution of the ToF atom-probe, or for that matter any ToF spectrometer or any other instrument, one should try to identify the main sources limiting the resolution and improve from there. It is also important to consider what are the principle functions of the instrument, i.e. whether it will be used mainly for mass analysis or for ion kinetic energy analysis. For the latter purpose, an artificial flight-time-focusing scheme cannot be used. 

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