An ambient ionisation source unit (10) is provided comprising: a housing (12) containing a first device (14) for generating analyte material from a surface of a sample to be analysed and a sampling inlet (16) for receiving analyte material liberated from the surface of the sample. The position(s) of the first device and/or sampling inlet is (are) fixed relative to the housing. Thus, the first device and the sampling inlet are integrated into a single unit that can be installed onto the front-end of an ion analysis instrument with minimal or reduced user interaction.