From Mass Spectrometry: A Foundation Course


An important component of all mass spectrometers, not often considered during operation, are the vacuum pumps. Many instruments use at least two pumps; one to evacuate the instrument chamber of air after assembly or venting and a second to reduce the pressure to that required to operate. Pressures vary within different mass spectrometers, and within each component, but it is typical for instruments to operate over a range of 10 ?3 to 10 ?6 Pa (1 Pa = 133.3226 torr or millimetres of mercury, mmHg). As described in Section 3.1, mass spectrometers operate under vacuum to prevent the collision and reaction of ions with residual gas molecules during their flight from the ion source to the detector. Low pressures also prevent condensation from building up inside the instrument that would coat critical lens and surfaces and create electrical discharges. The detector, too, must be protected from moisture and oxidation for it to operate properly.

3.6.1 Rotary Pumps

The most efficient way in which to reduce the pressure in a mass spectrometer to the 1 Pa level is with a rotary or roughing pump. In this pump, a rotating inner barrel draws the gas in from one side of a chamber and compresses it on the other (Figure 3.28). The compressed gas passes through a hydrocarbon oil reservoir, where the vapour pressure of the oil influences the lowest pressure that can be obtained. Rotary pumps have the capacity to dispel approximately 100...

Products & Services
High Vacuum Pumps
High and ultrahigh vacuum pumps operate efficiently in the high vacuum region and develop molecular flow for highly evacuated systems.
Vacuum Pumps and Vacuum Generators
Vacuum pumps and vacuum generators provide sub-atmospheric pressure for a variety of industrial and scientific applications where a vacuum is required.
Mechanical Vacuum Pumps and Systems
Mechanical vacuum pumps and systems contain devices such as pistons, claws, scrolling spirals, and diaphragms to isolate and compress air.
Rotary Vane Vacuum Pumps and Systems
Rotary vane vacuum pumps and systems move media through the pump using a rotating assembly in the pumping chamber. Typically, there are two or more rotating vanes that move the media from inlet to outlet. Rotary vane vacuum pumps are positive displacement pumps.
Vacuum Sensors
Vacuum sensors are devices for measuring vacuum or sub-atmospheric pressures.

Topics of Interest

FURTHER READING J.T. Watson, Introduction to Mass Spectrometry, 3rd edition, Lippincott-Raven, Philadelphia, 1997 E. DeHoffmann and J. Charette, Mass Spectrometry - Principles and Applications, 2nd...

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