An ion source a first ionizer comprising: an electrospray needle comprising a tip; and a conduit disposed annularly about the needle and configured to pass an inert gas in proximity of the tip to nebulize a fluid emerging from the tip, the nebulized fluid comprising analytes and a mobile phase. The ion source comprises a capillary in tandem with the first ionizer and configured to receive the droplets; a heater configured to heat the capillary to a temperature at which mobile phase vaporizes; and a second ionizer in tandem with the capillary and configured to receive the vaporized mobile phase and the analytes. A method is also described.