Measurement of unimolecular decay in peptides of masses greater than 1200 units by a reflecting time‐of‐flight mass spectrometer

Abstract
Daughter ions from decomposition of [M + H]+ parent ions have been observed in a time‐of‐flight mass spectrometer fitted with an ion mirror. Unit mass resolution is obtained for parent ions of masses up to several thousand u when the mirror voltage is set at a value determined by the usual velocity‐focusing criterion for parent ions. Under this condition the daughter‐ion resolution in the low‐mass range suffers. Considerable improvement is obtained when the daughter‐ion spectrum is examined in several segments, with the mirror voltage optimized for each segment. The daughter‐ion spectrum from decay of metastable [M + H]+ parent ions in Substance P is measured using this technique. Reasons are suggested for differences between the spectrum obtained and a spectrum for the same compound recently obtained using a tandem double‐focusing instrument.

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