Pulsation modes and the effect of applied voltage on current and flow rate in nanoelectrospray.

New modes of nanoelectrospray (nES) have been identified that exhibit stable high-frequency current oscillations in the kilohertz range. In-line flow rate measurements during nES have for the first time allowed the accurate determination of the spray current and volumetric flow rate dependence on applied voltage. High-speed video imaging has revealed that each current pulse corresponds to the periodic formation of a short-lived stable cone-jet structure at the capillary tip. These findings are of particular importance and suggest greater process monitoring and control in nES-MS systems is necessary if efficiency and ion yield are to be optimized.