Positive and negative ion methane chemical ionization mass spectrometry of amino acid pentafluorobenzyl derivatives

Abstract

Condensation of pentafluorobenzyl bromide with α-amino acids under basic conditions using a brief reaction time generates amino acid-PFB derivatives. These compounds have satisfactory gas chromatographic properties and their methane positive and negative ion mass spectra have been recorded. These spectra contain few fragment ions and the negative ion mass spectra are dominated by a single anionic species making them suitable for selected ion monitoring experiments for the quantification of amino acids. Using Leu and Tyr as two typical examples we have found that negative ion chemical ionization mass spectrometry generates an increase of 250 to 300 times that observed for the same compounds under positive ion conditions.