Pulsed High-Pressure Liquid Injection of Biological Molecules into Supersonic Beam/Mass Spectrometry with Resonant Two-Photon Ionization Detection

Abstract

Pulsed high-pressure liquid injection is used as a means of introducing thermally labile biological species into a time-of-flight mass spectrometer (TOFMS) system. The analyte species are then ionized by resonant two-photon ionization (R2PI) in the near ultraviolet. This method serves as a means of producing soft ionization or extensive fragmentation on the basis of the laser power and wavelength, without physical separation of the analyte from the effluent jet expansion. In addition, the pulsed liquid injection method allows introduction of the sample in methanol at 80°C without the extensive clustering that normally occurs in continuous expansions unless much higher temperature is utilized. With the use of this method the R2PI of catecholamines and indoleamines, as well as their metabolites, is studied in a TOFMS. The ability to obtain some spectral selectivity from jet expansions of liquid methanol is also demonstrated.