A continuous flow probe method for on-line introduction of liquid samples for detection by laser desorption with resonant two-photon ionization in supersonic beam mass spectrometry

A continuous flow probe is used as a direct inlet source for injection of liquid samples into a time-of-flight (TOF) mass spectrometer. The direct liquid inlet is coupled to laser desorption as a means of rapidly vaporizing the nonvolatile sample dissolved in the solvent for entrainment into a supersonic jet expansion. The target analyte is then selectively analyzed by resonance enhanced multiphoton ionization (REMPI) in the TOF device. This method demonstrates the ability to continuously inject thermally labile biological samples such as neurotransmitters and oligopeptides for detection and structural analysis by REMPI. In addition, sensitivity limits in the low ng regime are demonstrated with quantitation over 3 orders of magnitude.