The significance of monoisotopic and carbon-13 isobars for the identification of a 19-component dodecapeptide library by positive ion electrospray Fourier transform ion cyclotron resonance mass spectrometry

Harnessing the ultra high resolution capabilities of Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and positive ion electrosp ray, we have demonstrated the significance and utility of cumulative mass d efect high resolution mass separation stable isotope distribution, exact ma ss measurement and elemental formula as a means of simultaneously identifyi ng 19 components of the dodecapeptide library Ac-ANKISYQS[X]STE-NH2. With a n instrument resolution of 275000 (average), isobaric multiplets attributed to monoisotopic and carbon-13 components of peptides: Ac similar to SLS si milar to NH2; Ac similar to SNS similar to NH2: Ac similar to SOS similar t o NH2; Ac similar to SDS similar to NH2; within the mass window of 1380-138 5 Da, and Ac similar to SQS similar to NH2; Ac similar to SKS similar to NH 2; Ac similar to SES similar to NH2; Ac similar to SMS - NH2, within the ma ss window 1395-1100 Da, were mass resolved, accurately mass measured and id entified from the computed molecular formulas. This experimental procedure enabled the separation of monoisotopic and carbon-13 isobars yielding enhan ced selectivity and specificity and serves to illustrate the significance o f monoisotopic and carbon-13 isobars in final product analysis, Chromatogra phic separation (HPLC) was of limited utility except for monitoring the ove rall extent of reaction and apparent product distribution, Positive ion ele ctrospray-FTICR-MS and fast atom bombardment (FAB) MS were used to assess f inal product quality and apparent component distribution, Copyright (C) 200 0 John Wiley & Sons, Ltd.