A mass spectrometer is disclosed comprising a first component, an annular vacuum chamber seal and a second component. The first component has a groove. The annular vacuum chamber seal comprises a main body portion and one or more blade or rib portions which protrude from the main body portion. The main body portion is located in the groove and the one or more blade or rib portions protrude above or beyond a surface of the first component. The second component is slid, in use, along the surface of the first component thereby deforming the one or more blade or rib portions so that the one or more blade or rib portions form a radial, diametric or piston seal between the first and second components.