A dual electrospray ionization source for use in connection with a mass spectrometer having an inlet port. The source includes a polymer nozzle holder having a drive axis and a pair of continuously spraying nozzles mounted to the nozzle holder at spaced-apart positions. An adjustment mechanism allows positional adjustment of one nozzle with respect to the other nozzle on the nozzle holder. A programmable motor is connected to the nozzle holder at the drive axis. The motor rotationally and reciprocally drives the nozzle holder to sequentially position each of the nozzles in alignment with an inlet port of mass spectrometer.