FIELD DESORPTION MASS SPECTROMETRY: II. Potassium Cationization Field Desorption Mass Spectrometry of Some Penta‐ and Hexapeptides Derived from Substance P

In this article we present preliminary results of the application of potassium cationized field desorption mass spectrometry as an additional technique for the elucidation of structure and evaluation of purity of oligopeptides such as C‐terminal penta‐ and hexapeptide analogs of substance P. In the resultant mass spectra both a protonated and a cationized molecular ion, MH+ and MK+respectively, were observed. The m/z values of the two peaks were in agreement with the calculated molecular weights. The ratio between the relative abundancies of these ions (MH+/MK+) was found to be characteristic of the particular peptide and thus useful in the assessment of their purity. Among the 13 peptides studied, only two gave pyroly tic fragmentation leading to a more complex spectra.