Formation and collision-induced dissociation of adduct ions [matrix + C] + (C  Li, Na, Cs and NH 4) produced under fast atom bombardment conditions

Abstract

The formation of adduct ions of matrices B with organic/metallic cations C +, [B + C] + (C  Li, Na, Cs and NH 4), under fast atom bombardment (FAB) conditions has been examined. The cation affinity (CA) for various matrix materials, glycerol, thioglycerol, dithiothreitol, m-nitrobenzylalcohol and diethanolamine, was evaluated from the positive-ion FAB mass spectra obtained for the salts LiCl, NaCl, CsCl or NH 4Cl added to matrix B. The order of the CA of matrices for relatively small cations Li + and Na + was in accordance with that of the proton affinity (PA) of the matrices used. The collision-induced dissociation (CID) spectra of [B + H] + and [B + C] + ions have been obtained. The PA differences between matrix B and ammonia (NH 3) molecules were roughly estimated from the CID spectra of [B + NH 4] + ions. The CID spectra of [B + C] + ions, which have different dissociation windows from [B + H] + ions, were analyzed by proposing multidentate-binding structures of the adduct ions. Some dissociations of [B + C] + ions could be explained by charge-remote fragmentations. The results obtained suggest that the binding energy for the coordination complex (B⋯C +) can be evaluated from the CID patterns.