Abstract: Improved techniques are provided for forming ionized molecules from electrosprayed droplets for analysis by a mass spectrometer. A high voltage is applied to a capillary tube for spraying droplets at substantially atmospheric pressure or above, and the electrosprayed droplets contain sample solute of interest and solvent. The electrosprayed droplets are passed into an ion generating chamber which is maintained at a pressure in the range of from 0.2 Torr to 10 Torr. The walls of the ion generating chamber are controllably heated to a temperature which will desolvate the droplets and produce ionized molecules of interest for analysis by the mass spectrometer. The electrospray technique does not rely upon a countercurrent heated gas flow, and provides a particularly simple and inexpensive means to couple electrospray ionization to either quadrupole or magnetic mass analyzers.

Abstract: A mass spectrometer having a thermospray ion source, suitable for the analysis of liquid samples is disclosed. The source comprises a strongly heated atomizing nozzle (4) through which the sample is pumped into a spray chamber (5, 11), and an aperture in a cone (26), through which the ions pass through an electrostatic lens (15, 16, 17) into a region (23) in which a mass analyzer is situated. Electrode means (27, 45) generate a repulsive electrostatic field which improves the efficiency of the transmission of ions through the hole in the cone (26). The electrode is situated downstream of the hole in cone (26). By further increasing the potential on the electrode (27, 45) the nature of the ions passing through the hole in the cone (26) can be changed from largely adduct and cluster ions formed by association of solvent molecules with sample ions in the thermospray to largely pseudomolecular sample ions similar to those formed by conventional chemical ionization.