An ion source for a mass spectrometer and a method of ionizing a sample are disclosed. A droplet generator is configured to emit a stream of analyte droplets, which are ionized upon impact with a target, thus forming an ion stream. Preferably, the droplets have a diameter that is greater than a preset value to increase the kinetic energy of the droplets. Additionally, the droplet generator can be configured to create a gas flow that increases the kinetic energy of the droplets. In one embodiment, the target is positioned upstream of an inlet of a mass spectrometer so that the ion stream enters the inlet. In another preferred embodiment, the target is positioned downstream of the inlet so that the stream of droplets passes through the inlet of the mass spectrometer, and the inlet is provided with a pressure drop that increases the kinetic energy of the droplets.