involve the following five steps 1 nearly complete vaporization of the liquid at the rate with which it is supplied to the vaporizer produces a super heated mist carried in a supersonic jet of vapor nonvolatile molecules are preferentially retained in the droplets of the mist 2 droplets of the mist are charged positively or negatively according to the statistical expectations for random sampling of a neutral fluid containing discrete positive and negative charges 3 molecular ions clustered with a few solvent molecules evaporate from the superheated droplets assisted by the high local electrical fields generated by the charge on the droplet 4 cluster ions rapidly equilibrate with the vapor in the ion source to channels available 5 ions diffusing to the sampling apparatus are then transmitted to the mass analyzer or other detecting apparatus 6 even if the 34 soft 34 ionization created by the thermospray is insufficient to ionize a desired molecule additional ionization may be provided by an electron beam or laser as indicated at 26 this invention is concerned with the process occurring when a flowing liquid is vaporized as it is forced under pressure through a heated capillary tube the temperature profiles produced by direct electrical heating of the capillary are illustrated in fig1 in this experiment 53 watts was dissipated in the capillary with water flowing through at rates in the range from 0 7 to 4 0 ml min as indicated by the parameter in fig1 the experimental result at 0 7 ml min is compared with a calculated profile in fig1 where the processes occurring in different regions of the heated capillary are represented schematically at the inlet end the flowing water is heated until vaporization begins from this point and downstream the temperature remains nearly constant until vaporization is.