High-Sensitivity Detection of 4-(3-Pyridinylmethylamino-carboxypropyl) Phenylthiohydantoins by Capillary Liquid Chromatography–Microelectrospray Ion Trap Mass Spectrometry

We describe the separation and detection at the low-femtomole level of 4-(3-pyridinylmethylaminocarboxypropyl) phenylthiohydantoins (311-PTHs) by capillary liquid chromatography–microelectrospray ion trap mass spectrometry. Highest sensitivity was obtained in the multiple-ion monitoring operating mode in which we detected 311-PTHs at the 5-fmol level with a signal-to-noise ratio of approximately 10. We investigated the fragmentation patterns of the isobaric 311-PTH isoleucine and 311-PTH leucine by electrospray ionization ion trap tandem mass spectrometry. The compounds could be differentiated by a fragment ion of mass m/z=366.1 which was specific for the breakdown of 311-PTH leucine, thus allowing for the unambiguous identification of the 311-PTH derivatives of all 20 naturally occurring amino acids by their masses and fragmentation patterns.