Quadrupole—ion trap

An ion trap is a device where gaseous ions can be formed and/or stored for periods of time, confined by electric and/or magnetic fields. There are three commercial types of ion traps in use in MS, the QIT the Orbitrap, which uses a spiral trajectory that oscillates along a ID linear axis and the ICR trap. 

Ions are extracted from the trap by changing the amplitude of the ring electrode RF. As the amplitude increases, the trajectory of ions of increasing m/z becomes unstable. These ions move toward the end caps, one of which has openings leading to the detector. Ions of a given m/z value pass through the end cap sequentially and are detected. 

The use of various RF and DC waveforms on the end caps allows the ion trap to selectively store precursor ions for MS/MS experiments or to selectively store analyte ions while eliminating 

Appropriate use of RF and DC voltages means that some ions can be selectively retained and product ions generated. Some of these ions can then be selected and their product ions generated. In this manner, a fragmentation chain can be established. The ion trap is a typical tandem-in-time mass spectrometer, in which precursor and product ions are created and analysed in the same physical space ionisation and ion analysis, on the other hand, take place at different times ( MS/MS in time )- The operation can be repeated several times, making it possible to perform MS11. Ion trap mass spectrometry thus consists of  

Despite the fact that the ion trap via tandem MS offers more extensive possibilities for identification than QMS, in practice it is not often applied, because routine interpretation of the spectra is often complex and time-consuming. 

Accurate mass assignment of highly resolved ion-intensity signals remains problematic. QITMS is a relatively simple and compact apparatus (benchtop) and an order of magnitude less expensive than the multistage (triple quad or tandem double-focusing) instruments traditionally used for structural determination. 

Instrumental developments concern micro ion traps (sub-mm i.d.) [193], extension of the mass range, mass resolution and capture efficiency for ions generated externally. Fast separations at very low detection levels are possible by means of hybrid QIT/reToF mass spectrometry [194]. 

QITMS has been reviewed [195-197], and has been the subject of various books [198,199] a tutorial has also appeared [200]. 

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B1.7.4 QUADRUPOLE MASS FILTERS, QUADRUPOLE ION TRAPS AND THEIR APPLICATIONS... 

Asano K, Goeringer D and McLuckey S 1998 Dissociation kinetics in the quadrupole ion trap Proc. 46th Conf Am. Soc. Mass Spectrom. 

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... 

Gronert S 1998 Estimation of effective ion temperatures in a quadrupole ion trap J. Am. Soc. Mass Spectrom. 9 845-8... 

Son M, Frankevich V, Nappi M, Santini R E, Amy J W and Cooks R G 1996 Broad-band Fourier transform quadrupole ion trap mass spectrometry Anal. Chem. 68 3341 -20... 

This is a three volume set severing the physios and ehemistry for quadrupole ion traps. It is a must for anyone using traps as part of their researeh. 

Almost any type of analyzer could be used to separate isotopes, so their ratios of abundances can be measured. In practice, the type of analyzer employed will depend on the resolution needed to differentiate among a range of isotopes. When the isotopes are locked into multielement ions, it becomes difficult to separate all of the possible isotopes. For example, an ion of composition CgHijOj will actually consist of many compositions if all of the isotopes ( C, C, H, H, 0, O, and 0) are considered. To resolve all of these isotopic compositions before measurement of their abundances is difficult. For low-molecular-mass ions (HjO, COj) or for atomic ions (Ca, Cl), the problems are not so severe. Therefore, most accurate isotope ratio measurements are made on low-molecular-mass species, and resolution of these even with simple analyzers is not difficult. The most widely used analyzers are based on magnets, quadrupoles, ion traps, and time-of-flight instruments. 

The quadrupole ion-trap, usually referred to simply as the ion-trap, is a three-dimensional quadrupole. This type of analyser is shown schematically in Figure 3.5. It consists of a ring electrode with further electrodes, the end-cap electrodes, above and below this. In contrast to the quadrupole, described above, ions, after introduction into the ion-trap, follow a stable (but complex) trajectory, i.e. are trapped, until an RF voltage is applied to the ring electrode. Ions of a particular m/z then become unstable and are directed toward the detector. By varying the RF voltage in a systematic way, a complete mass spectrum may be obtained. 

Figure 3.5 Schematic of a (quadrupole) ion-trap mass analyser. From applications literature published by Thermofinnigan, Hemel Hempstead, UK, and reproduced with permission.

Flow injection Chemical ionisation (Cl) Quadrupole ion trap (QITMS) Diode array detector... 

In mass spectrometers, ions are analysed according to the ml7. (mass-to-charge) value and not to the mass. While there are many possible combinations of technologies associated with a mass-spectrometry experiment, relatively few forms of mass analysis predominate. They include linear multipoles, such as the quadrupole mass filter, time-of-flight mass spectrometry, ion trapping forms of mass spectrometry, including the quadrupole ion trap and Fourier-transform ion-cyclotron resonance, and sector mass spectrometry. Hybrid instruments intend to combine the strengths of the component analysers. 

Ion trap MS is particularly suited for chemical structure elucidation, as it allows for simultaneous ion storage, ion activation and fragmentation, and product ion analysis. The fragmentation pathway of selected ions and the fragmentation products provide information on the molecular structure. Compared with triple-quadrupole and especially with sector instruments, the ion trap instrument provides more efficient conversion of precursor ion into product ions. However, the CID process via resonance excitation, although quite efficient in terms of conversion yield, generally results in only one (major) product ion in the product-ion mass spectrum. MS/MS with a quadrupole ion trap offers a number of advantages ... 

QITMS Quadrupole ion trap mass SCOT Support-coated open-tubular... 

Quadrupole Ion Trap Mass Spectrometry. Second Edition. By Raymond E. March and John F. J. Todd... 

Figure 8.4 Positive ion direct atmospheric pressure LD mass spectrum of in vitro grown P. falciparum parasites. Protocol C is used for sample preparation estimated number of parasites deposited is approximately 103. A commercially available AP LD quadrupole ion trap (LCQ) system is used.19,20 Typical laser beam spot diameter is 0.5 mm acquisition time is approximately 20 s LCQ inlet capillary temperature -200°C.

Moyor, S. C. Marzilli, L. A. Woods, A. S. Laiko, V. V. Doroshenko, V. M. Cotter, R. J. Atmospheric pressure matrix-assisted laser desorption/ionization (AP MALDI) on a quadrupole ion trap mass spectrometer. Int. I. Mass Spectrom. 2003, 226,133-150. 

Different mass analysers can be combined with the electrospray ionization source to effect analysis. These include magnetic sector analysers, quadrupole filter (Q), quadrupole ion trap (QIT), time of flight (TOF), and more recently the Fourrier transform ion cyclotron resonance (FTICR) mass analysers. Tandem mass spectrometry can also be effected by combining one or more mass analysers in tandem, as in a triple quadrupole or a QTOF. The first analyzer is usually used as a mass filter to select parent ions that can be fragmented and analyzed by subsequent analysers. 

Warscheid, B. Jackson, K. Sutton, C. Fenselau, C. MALDI analysis of Bacilli in spore mixtures by applying a quadrupole ion trap time-of-fhght tandem mass spectrometer. Anal. Chem. 2003, 75, 5608-5617. 

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