Method and apparatus for analysis and ion source

An ion source comprises a chamber 2 containing an electrode 4; an inlet such as capillary tube 6 for atmospheric air containing a sample for analysis; and a vacuum source connected to the chamber. The vacuum source maintains pressure in the chamber below atmospheric pressure when the inlet is open to atmosphere. An electrical discharge excites air molecules in the chamber, which react with the sample to generate sample ions. The ions can be swept by electrical or electrostatic lenses into an analyser such as a mass spectrometer whose pressure is lower than that of the chamber. The discharge can be created by applying a DC voltage to the electrode. The inlet can be heated. The apparatus can be used for sniffing applications for analysis of air and for solid or liquid samples that are dispersed in air by direct injection, nebulisation, vaporisation or ablation.