SONIC SPRAY IONIZATION METHOD FOR ATMOSPHERIC-PRESSURE IONIZATION MASS-SPECTROMETRY

We have developed a novel spray ionization method for interfaces in capillary electrophoresis/mass spectrometry and liquid chromatography/mass spectrometry. This method is called ''sonic spray'' ionization. In this method it is not necessary to apply an electric field to the capillary of the ion source, which operates at room temperature. A solution in methanol and water from a fused-silica capillary is sprayed; under atmospheric pressure with nitrogen gas flow coaxial to the capillary. Gaseous ions as well as droplets are produced from the solution by the spray, and the positive ions are analyzed with a double-focusing mass spectrometer. We found that the detected ion intensity depends on the Mach number or the gas velocity. Ions are detected at a gas velocity higher than a certain value, and the ion intensity has a maximum at a Mach number of about 1, i.e., the sonic velocity. Preliminary results for solutions of dopamine, lysine, and gramicidin S are presented.