Electrostatic analyser

The double-focusing mass spectrometer consists of both magnetic sector and electrostatic analysers (ESAs), the latter being a device which focuses ions with the same m jz values but differing energies. The extent to which the beams of ions of closely similar m jz ratios overlap is thus reduced so that in many cases they may be separated. This then allows their mjz ratios to be determined with more accuracy and precision and the atomic composition of the ion to be determined. 

Although it is hkely that the majority of those involved in LC-MS and LC-MS-MS will have one of the instruments described above, it is also worthwhile mentioning two other types of instrument that have MS-MS capabilities, with these being instruments containing both a magnetic sector and an electrostatic analyser (see Section 3.3.3 above), and four-sector systems. 

Electrostatic analyser (ESA) An energy-focusing device used in a double-focusing mass spectrometer to increase mass specnal resolution. 

Linked scanning A series of techniques in which the electrostatic analyser voltage and magnetic field strength of a double-focusing mass spectrometer are scanned to obtain MS-MS spectra. 

Reverse-geometry double-focusing mass spectrometer A double-focusing mass spectrometer in which the magnetic analyser precedes the electrostatic analyser. 

Tri-sector mass spectrometer A mass spectrometer consisting of an electrostatic analyser (ESA), a magnetic sector and a second ESA in series. 

Various tandem MS instrument configurations have been developed, e.g. sector instruments, such as CBCE, CBCECB or CECBCE, and hybrid instruments, e.g. BCECQQ (B = magnetic sector analyser, E = electrostatic analyser, C = collision cell, Q = quadrupole mass spectrometer), all with specific performance. Sector mass spectrometers have been reviewed [168],... 

E, ESA Electric sector analyser, electrostatic ESA Electrostatic analyser... 

A typical configuration, often used in general-purpose AMS systems, is shown in Figure 16.3 an electrostatic analyser after the exit of the ion source followed by an injection magnet. 

Analysis on the high energy side is of course performed by a combination of, at least, two of the already described electromagnetic filters. In Figure 16.3, a configuration consisting of a magnet followed by an electrostatic analyser is illustrated. 

Source of high-energy electrons, ion accelerator, magnetic/electrostatic analyser, detector and recorder, high vacuum pumping system. 

Double-focusing mass spectrometer with EB configuration in which a deflection of 90° electrostatic analyser (E) is followed by a 90° magnetic analyser (B) (or reverse geometry - BE). 

Greater resolution can be achieved when a magnetic analyser is coupled with an electrostatic analyser (in a double focusing" mass spectrometer).. Using this combination of analysers, mass accuracies of around 1 part per million (ppm) can be obtained. However, magnetic sector instruments have relatively low sensitivity and are very expensive. 

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