THE ACID EFFECT IN FAST-ATOM-BOMBARDMENT

The effects on fast atom bombardment (FAB) mass spectra of analyte bases in glycerol on adding acids were investigated. The MH+ ion intensity usually increased but sometimes decreases were also found. For the practical use of FAB, it is important to clarify the reasons for this acid effect. By critical evaluation, a variety of different explanations were found, e.g. changes in solubility, surface activity, volatility, radiation-induced chemistry and desorption energetics. No unambiguous examples of efficient preformed ion formation were found. However, it is still possible that preformed ion formation may be important in the uppermost surface layer. The mechanistic implications of these findings are briefly discussed.