COMBINATION OF NOZZLE-SKIMMER FRAGMENTATION AND PARTIAL ACID-HYDROLYSIS IN ELECTROSPRAY-IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY OF SYNTHETIC PEPTIDES

For reliable confirmation of peptide structures, nozzle-skimmer collis ionally induced dissociation was found in many cases to be insufficien t, and partial acid hydrolysis was employed as a complementary techniq ue. The utility of combining these fragmentation methods is demonstrat ed in two examples where the complete sequences of two synthetic pepti des (peptide I, MW 2290 and peptide II, MW 1482) were unambiguously de termined. In a third example, three different valine deletions in a 2 kDa synthetic peptide were identified and their positions unambiguousl y established. A home-built electrospray ionization time-of-flight mas s spectrometer with orthogonal extraction was used for these analyses. The performance of this instrument with a resolving power of up to 75 00, a mass accuracy of less than or equal to 10 ppm, and a detection l imit of 1 fmol was shown to be well suited for such studies. As a subs titution to conventional external calibration, a more convenient and e qually accurate internal 3-point calibration is proposed, based on the low mass ions that are present in almost all peptide spectra. (C) 199 8 John Wiley & Sons, Ltd.