Abstract: An ion gun comprises an at least part annular ion source (1,2,3), the source being arranged so that ions are extracted from around the source in a direction perpendicular to the plane of the source. Electrodes (8,9,10) adapted to direct ions towards a location that lies on the central axis perpendicular to the plane of the source. The ion gun can be used alone or in combination with an ion detector (13) to provide a mass spectrometry apparatus.

Abstract: A sample inlet apparatus comprises a sample source (1) and a first enclosure (3), connected to the sample source via a first inlet (2). An analyser enclosure (7) is connected to the first enclosure (3) via a second inlet (5,15) substantially in alignment with the first inlet (2). Also provided is a second enclosure (10), connected to the analyser enclosure (7) via a third inlet (9) substantially in alignment with the first (2) and second (5,15) inlet, and vacuum pumps (4,11) for maintaining the first (3) and second enclosures (10) at a pressure lower than the sample source (1) and higher than that of the analyser enclosure (7) in use, whereby a molecular beam of sample molecules is generated along the axis of the inlet.