A progammable, high-resolution liquid-handling device, suitable for both aqueous and organic solvents, is described. This device, called an isolated-droplet generator (IDG), is based on the vibrating-capillary principle of droplet production. The unit described is capable of converting a liquid stream, such as that produced by an HPLC, to a subnanolitersized monodisperse droplet stream generated at rates of up to 50 kHz. Charging and deflection circuitry can be used to select individual droplets or droplet packets from the main stream. The instrument is an improvement over older designs, in that computer control imparts sufficient flexibility to make the device useful as a general-purpose high-resolution liquid-handling system. Droplet production parameters can be automatically altered to compensate for changing liquid streams, such as occur in liquid chromatography with gradient elution. The waveforms for droplet production and charging are produced entirely in hardware by a programmable counter/timer integrated circuit (IC).
P. M. Wiegand and S. R. Crouch, "Evaluation of a Programmable, Hardware-Driven, Isolated-Droplet Generator," Appl. Spectrosc. 42, 567-571 (1988)