Chemical magnetic sector mass spectrometer

Focal plane (array) detectors can detect a range of masses simultaneously. This provides a multichannel advantage that can improve the sensitivity for magnetic sectors, and detection limits can be improved if the analysis is limited by the analyte ion current instead of the chemical background level. This is the case for experiments such as MS/MS, electrospray ionisation, and field desorption. Array detectors can be used with pulsed ionisation methods, but the array detectors for commercial magnetic sector mass spectrometers can only detect a portion of the entire mass range at any given instant. 

In the internal ionization mode, ions are formed, stored, and excited resonantly to the point of ejection inside the ion trap in the presence of neutral sample molecules. Primary fragment ions confined in the ion trap experience the flow of neutral sample molecules through the ion trap for a period of time that varies from cfl 2 ms to ca 200 ms. The longer is this period of time, the greater is the probability of the occurrence of undesirable ion/molecnle reactions this process is known as self-chemical ionization, or self-Cl [20], Typically, self-CI will create [M -H H] + ions due to proton transfer. However, adduct ion peaks may be formed when an alkyl group is transferred. The self-CI process may affect library-search results of those compounds because the majority of mass spectra in mass-spectral libraries were acquired with quadru-pole mass filters or magnetic sector mass spectrometers wherein self-CI does not... 

Figure 7 Neutralization-reionization mass spectra of (A) HOS" and (B) HSO". Modified ZAB four-sector mass spectrometer of BEBE configuration (B = magnet sector E = electric sector). Oxygen used as collision gas used in each collision cell (see Figure 5). The pressure of the gas in each cell was adjusted so the reduction in the main beam is 20% for each collision event. Reproduced with permission of ACS from Goldberg N and Schwarz H (1994) Accounts of Chemical Research 27 347-352.

Another approach to mass analysis is based on stable ion trajectories in quadnipole fields. The two most prominent members of this family of mass spectrometers are the quadnipole mass filter and the quadnipole ion trap. Quadnipole mass filters are one of the most connnon mass spectrometers, being extensively used as detectors in analytical instnunents, especially gas clnomatographs. The quadnipole ion trap (which also goes by the name quadnipole ion store, QUISTOR , Paul trap, or just ion trap) is fairly new to the physical chemistry laboratory. Its early development was due to its use as an inexpensive alternative to tandem magnetic sector and quadnipole filter instnunents for analytical analysis. It has, however, staned to be used more in die chemical physics and physical chemistry domains, and so it will be described in some detail in this section. 

Modem mass spectrometers are usually one of four types magnetic sector, quadrupole, time-of-flight, or ion trap. A brief introduction to each is provided. Classical applications are discussed to illustrate how these devices have shaped the landscape of elemental and isotopic chemical analysis. 

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