DROPLET ELECTROSPRAY MASS-SPECTROMETRY

In droplet electrospray (DES), a stream of uncharged droplets with a controlled radius between 6 and 50 mu m and at frequencies in the 100 kHz range is produced by vibrating the capillary tip with a piezoelectric buzzer. The droplets are then charged by letting the droplet stream pass close to a 50 mu m diameter rod electrode that is at 3 kV and is producing an electric discharge in the ambient air. The charged droplets are destabilized by the charge and emit a fine spray of offspring droplets. These events can be observed with a stroboscopic technique. The observed droplet fission is very similar in appearance to that reported by Gomez and Tang. The gas phase ions produced by the droplet fission (droplet spray) are detected with a mass spectrometer. The mass spectra are close to identical to spectra observed with conventional electrospray. Additional development of DES could lead to a technique that is analytically competitive with conventional ESMS. The present DES results provide some important insights into the mechanism of conventional ES.