An ion source, a mass spectrometer and a method of enhancing the performance of an ion source for use with a mass spectrometer. The ion source has a housing incorporating an ion source enclosure defining a chamber and an outer cover remote from the chamber. A fluid flow passageway is provided between the ion source enclosure and the outer cover. The method of the invention comprising supplying to the ion source housing a regulated flow of fluid through the fluid passageways so as to maintain the ion source enclosure within a predetermined temperature range of substantially between 60° c. and 80° c. and preferably at 70° c.