Mass-spektrometriya

Vacuum in the Mass Spectrometer
All mass spectrometers need a vacuum to allow ions to reach the detector without colliding with other gaseous molecules or atoms. If such collisions did occur, the instrument would suffer from reduced resolution and sensitivity. Higher pressures may also cause high voltages to discharge to ground which can damage the instrument, its electronics, and/or the computer system running the mass spectrometer. An extreme leak, basically an implosion, can seriously damage a mass spectrometer by destroying electrostatic lenses, coating the optics with pump oil, and damaging the detector. In general, maintaining a good vacuum is crucial to obtaining high quality spectra.
One of the first obstacles faced by the originators of mass spectrometry was coupling the sample source to a mass spectrometer. The sample is initially at atmospheric pressure (760 torr) before being transferred into the mass spectrometer’s vacuum (~10^-6 torr), which represents approximately a billion-fold difference in pressure. One approach is to introduce the sample through a capillary column (GC) or through a small orifice directly into the instrument. Another approach is to evacuate the sample chamber through a vacuum lock (MALDI) and once a reasonable vacuum is achieved (< 10^-2 torr) the sample can be presented to the primary vacuum chamber (< 10^-5 torr).
A mass spectrometer is shown in Figure 2.22 with three alternative pumping systems. All three systems are capable of producing a very high vacuum, and are all backed by a mechanical pump. The mechanical pump serves as a general workhorse for most mass spectrometers and allows for an initial vacuum of about 10^-3 torr to be obtained. Once a 10^-3 torr vacuum is achieved, the other pumping systems, such as diffusion, cryogenic and turbomolecular can be activated to obtain pressures as low as 10^-11 torr.
Figure 2.22: A well-maintained vacuum is essential to the function of a mass spectrometer. A couple of the different types of vacuum systems are illustrated.
Summary
The mass analyzer is a critical component to the performance of any mass spectrometer. Among the most commonly used are the quadrupole, quadrupole ion trap, time-of-flight, time-of-flight reflectron, and FTMS. However, the list is growing as more specialized analyzers allow for more difficult questions to be addressed. For example, the development of the quad-TOF has demonstrated its superior capabilities in high accuracy tandem mass spectrometry experiments. Once the ions are separated by the mass analyzer they reach the ion detector, which is ultimately responsible for the signal we observe in the mass spectrum.
References
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McCloskey JA & Simon MI Enzimologiyada usullari: Mass-spektrometriya . Akademik matbuot, 1997 yil .
Kinter M. va Sherman NE. Tandem massa spektrometriyasi yordamida oqsillarni sekanslash va aniqlash . Wiley-Interscience, 2000 yil .