Separation of leucine and isoleucine by electrospray ionization-high fieldasymmetric waveform ion mobility spectrometry-mass spectrometry

An electrospray ionization (ESI) source was used to generate gas-phase mole cular anions of the amino acids leucine and isoleucine ((M-H)(-); m/z -130) , which were separated by high-field asymmetric waveform ion mobility spect rometry (FAIMS) and detected by quadrupole mass spectrometry (MS). This com bination of ESI-FAIMS-MS enabled selective determination of either amino ac id in mixtures that contained at least a 625-fold excess of the other. Comp arisons with conventional ESI-MS showed a 50-fold improvement in the signal to background ratio for a 1 mu M solution of leucine. (C) 1999 American So ciety for Mass Spectrometry.