Formation by Fast Atom Bombardment of molecular radical cations by electron donor-acceptor complexes from tosylated amino acid esters

N-Alkyl-N-tosyl amino acid esters were ionized by fast atom bombardment (FAB) in a nitrobenzyl alcohol matrix through oxidative processes leading to molecular radical cations (M(+.)). The addition to the matrix of Cu-II salts induces the ionization through proton attachment whereby [M + H](+) are exclusively displayed by the positive-ion FAB spectra. The formation of electron donor-acceptor complexes between the analytes and the matrix lowers the critical energy for the ionization by one-electron removal from the substrates.