Ion Formation in DART

By ion-molecule reactions, the primary ions then deliver protonated water clusters, the most abundant being H502 . These clusters act as reagent ions for analyte ion generation by chemical ionization mechanisms [58]. 

In negative ion mode, thermal electrons are presumed to generate mostly O2 ions from air that serve as reagent ions. Of course, direct electron capture by the analyte as well as dissociative electron capture, deprotonation, or anion attachment are also feasible [58]. Thus, it has been inferred from the close similarity of the negative-ion products of DART and APPI that the same group of mechanisms of ion formation are effective. 

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