Structures of [M–44]+ ions in the electron impact and fast atom bombardment mass spectra of the β‐blocker nipradilol with a nitrate ester group

Abstract
Both electron impact (EI) and fast atom bombardment (liquid secondary ion mass spectrometry) (FAB(LSIMS)) spectra of tbe antihypertensive drug nipradilol (3,4‐dihydro‐8‐(2‐hydroxy‐3‐isopropylamino)propoxy‐3‐nitroxy‐2 H‐l‐benzopyran) and it analogues exhibit intense [M ‐ 44]+ peaks. However, high‐resolution measurements and tandem mass spectrometric techniques clarified that the composition of the ion produced by EI is [M‐C2H4O]+, whereas that of the ion produced by FAB(LSIMS) is [M ‐ NO2 + 2H]+. FAB collision‐activated dissociation‐tandem mass spectrometry revealed that the structure of the latter ion corresponds to the MH+ of the hydrolysis product of the nitrate ester group.