Ion-trap spectrometer

Olsen, E. Serially interfaced gas chromatography/Fourier Transform infrared spectrometer/ion trap detector. Finnigan MAT IDT 35. 

Elemental mass spectrometry has undergone a major expansion in the past 15-20 years. Many new a, elopments in sample introduction systems, ionization sources, and mass analyzers have been realized. A vast array of hybrid combinations of these has resulted from specific analytical needs such as improved detection limits, precision, accuracy, elemental coverage, ease of use, throughput, and sample size. As can be seen from most of the other chapters in this volume, however, the mass analyzers used to date have primarily been magnetic sector and quadrupole mass spectrometers. Ion trapping devices, be they quadrupole ion (Paul) [1] traps or Fourier transform ion cyclotron resonance (Penning) traps, have been used quite sparingly and most work to date has concentrated on proof of principal experiments rather that actual applications. 

Figure 2 A schematic diagram of the SCIEX linear ion trap mass spectrometer. Ion trapping can be wrought in either of Qc or Q3. The apparatus is based on the ion path in a TSQ mass spectrometer and the ion beam travels from left to right. Typical operating pressures are given. (Reproduced with permission from Hager JW (2002) A new linear ion trap mass spectrometer. Rapid Communications in Mass Spectrometry 6. 512-526. 2002, Wiley Sons Ltd.)...

If one wishes to carry ont gas-phase experiments, that is, to manipulate mass-selected ions inside the mass spectrometer, ion-trap analyzers offer the broadest arsenal of experiments including unimolecular fragmentations as well as bimolecular reactions with sufficiently volatile neutral reagents. Consequently, the choice of analyzer is also an important point. Mass analyzers use static or dynamic electric or magnetic fields to separate the ions either in time or in space. Sector-field mass analyzers use magnetic (B) and electrostatic (E) sectors to separate the ions... 

E. Olsen, Serially Interfaced Gas Chromatography Fourier Transform Infrared Spectrometer Ion-Trap Mass Spectrometer, Finnegan MAT IDT Publication 35. 

Thermoduest Finnigan Corporation USA Sector mass spectrometers Ion trap mass spectrometers Tiima.AMlinht macc Fourier transform ion cyclotron resonance mass spectrometers Triple quadrupole mass spectrometers Inductively coupled plasme... 

In essence, a guided-ion beam is a double mass spectrometer. Figure A3.5.9 shows a schematic diagram of a griided-ion beam apparatus [104]. Ions are created and extracted from an ion source. Many types of source have been used and the choice depends upon the application. Combining a flow tube such as that described in this chapter has proven to be versatile and it ensures the ions are thennalized [105]. After extraction, the ions are mass selected. Many types of mass spectrometer can be used a Wien ExB filter is shown. The ions are then injected into an octopole ion trap. The octopole consists of eight parallel rods arranged on a circle. An RF... 

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. 

Figure Bl.7.14. Schematic cross-sectional diagram of a quadnipole ion trap mass spectrometer. The distance between the two endcap electrodes is 2zq, while the radius of the ring electrode is (reproduced with pennission of Professor R March, Trent University, Peterborough, ON, Canada).

Figure Bl.7.16. Mass spectra obtained with a Finnigan GCQ quadnipole ion trap mass spectrometer, (a)...

Brodbelt J, Liou C-C and Donovan T 1991 Selective adduct formation by dimethyl ether chemical ionization is a quadrupole ion trap mass spectrometer and a conventional ion source Ana/. Chem. 63 1205-9... 

Other types of mass spectrometer may use point, array, or both types of collector. The time-of-flight (TOF) instrument uses a special multichannel plate collector an ion trap can record ion arrivals either sequentially in time or all at once a Fourier-transform ion cyclotron resonance (FTICR) instrument can record ion arrivals in either time or frequency domains which are interconvertible (by the Fourier-transform technique). 

There are two common occasions when rapid measurement is preferable. The first is with ionization sources using laser desorption or radionuclides. A pulse of ions is produced in a very short interval of time, often of the order of a few nanoseconds. If the mass spectrometer takes 1 sec to attempt to scan the range of ions produced, then clearly there will be no ions left by the time the scan has completed more than a few nanoseconds (ion traps excluded). If a point ion detector were to be used for this type of pulsed ionization, then after the beginning of the scan no more ions would reach the collector because there would not be any left The array collector overcomes this difficulty by detecting the ions produced all at the same instant. 

Other types of mass spectrometer can use point, array, or both types of ion detection. Ion trap mass spectrometers can detect ions sequentially or simultaneously and in some cases, as with ion cyclotron resonance (ICR), may not use a formal electron multiplier type of ion collector at all the ions can be detected by their different electric field frequencies in flight. 

Linked Scanning, Ion Traps, and Hybrid Mass Spectrometers... 

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