An evaluation of the negative ion mass spectra of electron-capturing derivatives of the biogenic trace amines I—phenylethylamine

Abstract

A series of fluorinated derivatives have been examined for their suitability of use for quantification of biogenic trace amines, in particular phenylethylamine, in biological samples at the picogram (femtomolar) level using negative ion mass spectrometry. The negative ion mass spectra of the pentafluoropropionyl, heptafluorobutyryl, perfluorosuccinimido, pentafluorobenzyl and pentafluorobenzoyl derivatives of phenylethylamine are characterized by intense high-mass fragment ion peaks due to loss of HF, whereas the spectra of the 3-trifluoromethylbenzoyl, 4-trifluoromethylbenzoyl and 3,5-di-trifluoromethylbenzoyl derivatives exhibited fragment ions due to loss of H or 2H and the pentafluorobenzoyl derivative did not form a detectable molecular ion. After acetylating the fluorobenzoyl derivatives of phenylethylamine, the spectra of the resultant amides were found to contain primarily molecular ions, and the electron capture cross-sections and negative ion sensitivities increased. The most suitable derivatives were found to be the N-acetyl-N-pentafluorobenzoyl, which could be detected at the 75 fg (0.5 attomolar) level of phenylethylamine and the N-acetyl-N-3,5-di- (trifluoromethyl)benzoyl derivative.