Creation of a charged site

The FAB ionization process is thought to encompass two steps in one concerted action. There must be a transfer of sample to the gas phase and ions must be 

Stults et al. have recently reported a derivatization reactions (III) for incorporation of a quaternary ammonium group at the N-terminus of peptides [51]. The 

MS-MS daughter ion spectra of these derivatives are simplified relative to the underivatized compounds and show abundant, almost exclusively N-terminus-contain-ing ions. 

Incorporation of 0 can be accomplished using the process reported by Desiderio and Kai [53]. A small amount of peptide is dissolved in methanolic HQ (3 M) and twofold excess of H2 0. The mixture is placed in a sealed vial and heated to 37 °C. The reaction is allowed to proceed for 2—7 days and the mixture is periodically examined mass spectrometrically until a stable level of exchange is obtained. The reaction typically produces 

2 Derivatives for constant neutral loss class screening 

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