An ambient ionisation ion source comprising: a sample or target holder; a capillary or other inlet; a first device arranged and adapted to generate analyte ions from a sample or target provided on said sample or target holder, wherein said first device is arranged and adapted to direct a spray of droplets onto said sample or target in order to generate said analyte ions, wherein said ion source is configured such that at least some of said analyte ions are sampled into said capillary or other inlet, wherein said capillary or other inlet is arranged and adapted to transfer said analyte ions into a mass and/or ion mobility spectrometer, and wherein said first device comprises a desorption electrospray ionisation ("DESI") ion source; an enclosure surrounding and enclosing said sample or target holder, said sample or target, said first device, and said capillary or other inlet, wherein said enclosure includes one or more gas inlets and one or more gas outlets; and a second device arranged and adapted to supply said enclosure with a first gas via said one or more gas inlets such that said enclosure is maintained, in use, at a pressure greater than atmospheric pressure so as to purge said enclosure, wherein said second device is arranged and adapted to substantially continuously supply said enclosure with said first gas via said one or more gas inlets, wherein said ion source is arranged and adapted such that, in use, at least some of said first gas substantially continuously leaves said enclosure via said one or more gas outlets, and wherein the ion source is configured such that droplets and analyte ions that are not sampled into said capillary or other inlet are removed from said enclosure by said first gas; and wherein (i) said first device is provided with a solvent capillary, a nebuliser gas feed, and/or a capillary voltage feed, and/or (ii) the ambient ionisation ion source further comprises a device for controlling or adjusting said first device, characterised in that the solvent capillary, nebuliser gas feed, capillary voltage feed, or device for controlling or adjusting said first device is provided to the first device through said one or more gas outlets. a sample or target holder; a capillary or other inlet; a first device arranged and adapted to generate analyte ions from a sample or target provided on said sample or target holder, wherein said first device is arranged and adapted to direct a spray of droplets onto said sample or target in order to generate said analyte ions, wherein said ion source is configured such that at least some of said analyte ions are sampled into said capillary or other inlet, wherein said capillary or other inlet is arranged and adapted to transfer said analyte ions into a mass and/or ion mobility spectrometer, and wherein said first device comprises a desorption electrospray ionisation ("DESI") ion source; an enclosure surrounding and enclosing said sample or target holder, said sample or target, said first device, and said capillary or other inlet, wherein said enclosure includes one or more gas inlets and one or more gas outlets; and a second device arranged and adapted to supply said enclosure with a first gas via said one or more gas inlets such that said enclosure is maintained, in use, at a pressure greater than atmospheric pressure so as to purge said enclosure, wherein said second device is arranged and adapted to substantially continuously supply said enclosure with said first gas via said one or more gas inlets, wherein said ion source is arranged and adapted such that, in use, at least some of said first gas substantially continuously leaves said enclosure via said one or more gas outlets, and wherein the ion source is configured such that droplets and analyte ions that are not sampled into said capillary or other inlet are removed from said enclosure by said first gas; and wherein (i) said first device is provided with a solvent capillary, a nebuliser gas feed, and/or a capillary voltage feed, and/or (ii) the ambient ionisation ion source further comprises a device for controlling or adjusting said first device, characterised in that the solvent capillary, nebuliser gas feed, capillary voltage feed, or device for controlling or adjusting said first device is provided to the first device through said one or more gas outlets.