There is provided a method of introducing ions into a mass spectrometer, comprising ionising a sample using a Matrix Assisted Laser Desorption Ionisation (“MALDI”) ion source to form a plurality of ions, transporting said plurality of ions in a first, primary gas through a passageway and into an inlet of a mass spectrometer, introducing a second, auxiliary gas into said inlet, and controlling a flow rate of said second gas into said inlet so as to control a flow rate of said first gas through said passageway.