Dissociation of Ions Produced by Electron Attachment

As noted above, the ions formed by electron attachment are negative radical (odd-electron) ions. We have previously seen how much the M+ radical ions are reactive in electron ionization. The M radical ions are generally less so, mainly because the ionizing electrons are thermalized in electron attachment and consequently the internal energy of the resulting ions is weak. 

FIGURE 9.57 Mass spectra of alprazolam recorded in electron ionization (top) and in electron attachment (bottom). 

The problem for the chemist is that the Br ions at m/z 79 and m/z 81 (due to the two bromine isotopes) are absolutely not specific of the molecule and inform neither on the nature of the molecule nor its bromination degree. The same kind of problan is encountered with PCBs that mainly supply CP chlorine ions at m/z 35 and m/z 37 

FIGURE 9.58 Loss of Br from a congener of dibromodiphenylether ionized by electron attachment. 

FIGURE 9.59 Loss of CL from 3,3 5,5 -tetrachlorobiphenyl under electron attachment. 

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