Basic Operating Principles of Mass Spectrometers

A diagram showing the basic operating principle of a triple quadrupole mass spectrometer is shown in figure 4. The sample enters the ion source from the column, via a suitable interface if necessary, and, in GC, is usually fragmented by either an electron impact or... 

Before discussing the basic operating principles of those mass spectrometer types used in ICP-MS instrumentation, some important characteristics need to be introduced mass resolution, abundance sensitivity, mass range, and scanning speed [8]. 

Developments in mass spectrometry technology, together with the availability of extensive DNA and protein sequence databases and software tools for data mining, has made possible rapid and sensitive mass spectrometry-based procedures for protein identification. Two basic types of mass spectrometers are commonly used for this purpose MALDI-TOF-MS and ESI-MS. MALDI-TOF instruments are now quite common in biochemistry laboratories and are very simple to use, requiring no special training. ESI instruments, usually coupled to capillary/nanoLC systems, are more complex and require expert operators. We will therefore focus on the use of MALDI-TOF-MS, although the sample preparation is identical for both methods. The principle behind the use of MALDI-TOF-MS for protein identification is that the digestion... 

One can argue that this classification is quite arbitrary and does not follow the conventional or historical description of mass analyzers. We believe, however, that emphasizing the similarity of physical phenomena that are essential for ion separation helps greatly in better understanding their basic operational principle. Combinations of these analyzers are also very common, especially in tandem mass spectrometers that will be discussed briefly in Section 6. 

The mass analyser described in the preceding section is sometimes referred to as a linear quadrupole, since the electrodes consist of parallel rods. Another type of mass spectrometer based on the use of a quadrupolar electric field is the three-dimensional (3D) quadrupole ion trap, which is sometimes also known as a Paul trap. This is a device that has been in existence for several decades, but it is only in the past twenty years or so that it has moved from a small number of research laboratories out into the commercial domain. Ion traps are now popular devices for a whole range of mass spectrometry applications, their popularity being enhanced by their very compact size and the ease with which they can be used in MS experiments (see Section 3.5.3.2). Several PTR-MS instruments have been constructed with a quadrupole ion trap and so a description of the basic operating principles... 

The principles of operation of quadnipole mass spectrometers were first described in the late 1950s by Wolfgang Paul who shared the 1989 Nobel Prize in Physics for this development. The equations governing the motion of an ion in a quadnipole field are quite complex and it is not the scope of the present article to provide the reader with a complete treatment. Rather, the basic principles of operation will be described, the reader being referred to several excellent sources for more complete infonnation [13, H and 15]. 

The scope of the use of mass spectrometry in the protein analysis has grown enormously in the past few decades. MS has become an important analytical tool in biological and biochemical research. Its speed, accuracy and sensitivity are unmatched by conventional analytical techniques. The variety of ionization methods permits the analysis of peptide or protein molecules from below 500 Da to as big as 300 Da (Biemann 1990 Lahm and Langen 2000). Basically, a mass spectrometer is an instrument that produces ions and separates them in the gas phase according to their mass-to-charge ratio (m/z). The basic principle of operation is to introduce sample to volatilization and ionization source, and then the molecular fragments from the ionization of the sample are detected by various kinds of detector and the data are analyzed with computer software. 

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