Liq. chromatog. mass spectrometry (LC-MS) is a valuable tool in the anal. of proteins and peptides. The combination of LC-MS with different fragmentation methods provides sequence information on components in complex mixts. In this work, online packed capillary LC electrospray ionization Fourier transform ion cyclotron resonance MS was combined with two complementary fragmentation techniques, i.e. nozzle-skimmer fragmentation and electron capture dissocn., for the detn. of hormonal peptides in an acid ethanol ext. of mouse pancreatic islets. The most abundant peptides, those derived from proinsulin and proglucagon, were identified by their masses and addnl. sequence-tag information established their identities. Interestingly, the expts. demonstrated the presence of truncated C-peptides, des-(25-29)-C-peptide and des-(27-31)-C-peptide. These novel findings clearly illustrate the potential usefulness of the described technique for online sequencing and characterization of peptides in tissue exts. [on SciFinder (R)]