FIG. 8D shows that the inlet device 15 can be sealably attached to the mass spectrometer 10. In other embodiments, the inlet device can be monolithic with the wall of the housing 10h of the mass spectrometer 10 and/or wall 12h of the vacuum chamber 12 holding the mass analyzer 30. In some embodiments, a plate and an o-ring seal 18p can be used to attach the inlet device 15 to the mass spectrometer 10. The inlet device 15 can nest in a vacuum fitting that screws into the wall 12h with a small aperture(s) 15a for ions. The inlet device 15 can also be implemented as a vacuum fitting that screws directly into the wall 12w with a small aperture(s) 15a for ions. The Di-m distance measured from the external emitter 20e to the ion entry of the mass analyzer 30 in the vacuum chamber 12 may be between 1-10 cm, such as about 1 cm, about 2 cm, about 3 cm, about 4 cm, about 5 cm, about 6 cm, about 7 cm, about 8 cm, about 9 cm and about 10 cm. In some embodiments, the distance Di-m is between 10 mm and about 150 mm.
