Abstract: The subject invention teaches the use of mechanical vibration to enhance the electrostatic dispersion of sample solutions into the small, highly charged droplets that can produce ions of solute species for mass spectrometric analysis. Such vibration turns out to be surprisingly effective at ultrasonic frequencies for solutions with flow rates, conductivities and surface tensions too high for stable dispersion by electrostatic forces alone as in conventional electrospray ionization. Several embodiments of the invention are described for purposes of illustration. Other possible embodiments will become apparent to those skilled in the art.