Fourier transform ion-cyclotron resonance

Equation 2.15 showed the inverse relationship between the m/z value of an ion and the frequency (oc of its circular motion inside the magnetic field of strength B. 

If a simple plate arrangement, as shown in Fig. 2.25, is mounted inside the magnetic field, the phenomenon described above can be used to obtain a very effective mass analyzer. First, we can confine the ions in a very small region by imposing on the trapping plates a small voltage of the same sign as the trapped ion. 

As shown by Eq. 2.15, ions of different m/z values exhibit different cyclotron frequencies. The radii of their circular motion are very small, but can be increased by the application of an excitation electrical field generated by an alternate voltage Vac applied on the two side electrodes (see Fig. 2.25). For a well-defined Vac frequency, only a well-defined ion resonates with it The ion will acquire energy from the electrical field and the radius of its circular motion will increase (for 

different from what has been described for the other mass analyzers, where the ion detection is obtained by a suitable detector mounted outside the analyzers themselves, the ICR system acts either as the mass analyzer or as the ion detector. 

In the ion cyclotron resonance (ICR) analyzer, ions are trapped by a strong magnetic field. The magnetic field will cause the ions to move in a circular motion with a frequency that depends on their m/z.. Ions to be detected are excited to make them move closer to the detection plates. Then a small current will be induced in the plate each time an ion passes by. Since the ions with different m/z have different ICR frequencies, each generated current frequency will correspond to a certain m/z value. 

Principle. The principle of the ion cyclotron resonance was developed in the early 1930s by Lawrence and coworkers [252, 253]. The utilization of the ion cyclotron resonance (ICR) technique for mass spectrometry was introduced around 1950 by Sommer et al. [254, 255], and combination with the Fourier transform (FT) technique was developed by Comisarow and Marshall in 1974 [256], Coupling of external sources to an FTICR analyzer was first done in 1985 [257, 258], 

An interesting feature of this equation is that all ions of a certain m/z have the same cyclotron frequency, independent of their velocity. Hence, energy focusing is not essential for precise determination of m/z. 

The method for ion detection in an FTICR instrument is different from the majority of other mass spectrometers, where the ions hit a detector and are lost in the process. 

Because long acquisition times are required for maximum resolution, it is essential that the ions can survive in the trap for extended periods of time. A main reason for ion loss is collisions with residual gas in the cell. Therefore, it is essential to keep the pressure as low as possible, preferably in the region of 10-9 torr or below. It is also important not to allow too many ions to enter the cell. When more than 106 to 107 ions are present in the cell, the coulomb repulsion can shift or broaden peaks in the mass spectra. By using an ion gate, the number of ions entering the cell can be limited in a controlled way. 

Note Occasionally, the acronym FTMS is used instead of FT-ICR-MS. Of course, ICR without Fourier transformation would not have the tremendous success it has, but Fourier transformation alone cannot separate ions according to m/z, and hence there is no FTMS. 

It would be possible to scan the RF and measure the magnitude of the image current at each m/z value to obtain the mass spectral information but the process would be very slow. Instead, an RF pulse is used that contains a range of frequencies. The range of frequencies is chosen to excite the desired m/z range. When the pulse is off, all of the exited ions induce image currents in the receiver plates as they rotate. The output current, which contains all of the frequency and magnitude information from all of the ions present, can be converted mathematically to a mass spectrum by the application of the Fourier transformation. The use of an ICR ion trap and Fourier transformation is called FTICR-MS or just FTMS. As of early 2003, this was the only type of FTMS instrument commercially available. 

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B1.7.6 FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETERS... 

Vartanian V H, Anderson J S and Laude D A 1995 Advances in trapped ion cells for Fourier transform ion cyclotron resonance mass spectrometry Mass Spec. Rev. 41 1-19... 

Comisarow M B and Marshall A G 1996 Early development of Fourier transform ion cyclotron resonance (FT-ICR) spectroscopy J. Mass Spectrom. 31 581-5... 

Grover R, Decouzon M, Maria P-C and Gal J-F 1996 Reliability of Fourier transform-ion cyclotron resonance determinations of rate constants for ion/molecule reactions Eur. Mass Spectrom. 2 213-23... 

Fisher J J and McMahon T B 1990 Determination of rate constants for low pressure association reactions by Fourier transform-ion cyclotron resonance Int. J. Mass Spectrom. Ion. Proc 100 707-17... 

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). 

An added consideration is that the TOF instruments are easily and quickly calibrated. As the mass range increases again (m/z 5,000-50,000), magnetic-sector instruments (with added electric sector) and ion cyclotron resonance instruments are very effective, but their prices tend to match the increases in resolving powers. At the top end of these ranges, masses of several million have been analyzed by using Fourier-transform ion cyclotron resonance (FTICR) instruments, but such measurements tend to be isolated rather than targets that can be achieved in everyday use. 

A simple mass spectrometer of low resolution (many quadrupoles, magnetic sectors, time-of-flight) cannot easily be used for accurate mass measurement and, usually, a double-focusing magnetic/electric-sector or Fourier-transform ion cyclotron resonance instrument is needed. 

FTICR. Fourier-transform ion cyclotron resonance GC/IRMS. gas chromatography isotope ratio mass spectrometry... 

Asamoto, B. and Dunbar, R.C., Analytical Applications of Fourier Transform Ion Cyclotron Resonance Spectroscopy, VCH, New York, 1991. 

Instruments are available that can perform MS/MS type experiments using a single analyzer. These instruments trap and manipulate ions in a trapping cell, which also serves as the mass analyzer. The ion trap and fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers are examples. 

To check the identity and purity of the products obtained in the above reactions it is not sufficient to analyze for the sulfur content since a mixture may incidentally have the same S content. Either X-ray diffraction on single crystals or Raman spectra of powder-like or crystalline samples will help to identify the anion(s) present in the product. However, the most convincing information comes from laser desorption Fourier transform ion cyclotron resonance (FTICR) mass spectra in the negative ion mode (LD mass spectra). It has been demonstrated that pure samples of K2S3 and K2S5 show peaks originating from S radical anions which are of the same size as the dianions in the particular sample no fragment ions of this type were observed [28]. 

The kinetics study [38] utilized a Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometer to measure the pathway branching ratios. The ability to eject selected masses and the extremely high mass resolution of this technique ensured that the observed CD3CH2 was in fact a primary product of the reaction. Temporal profiles from this reaction are shown in Fig. 1. Noticeably absent from the mass spectrum are the cations C2D2H3 and... 

Jensen P.K., Pasa-Tolic L., Anderson G. A., Horner J. A., Lipton M.S., Bruce J.E., and Smith R.D., Probing proteomes using capillary isolectric focusing-elec-trospray ionization Fourier transform ion cyclotron resonance mass spectrometry, Anal. Chem. 71, 2076, 1999. 

Alternative approaches consist in heat extraction by means of thermal analysis, thermal volatilisation and (laser) desorption techniques, or pyrolysis. In most cases mass spectrometric detection modes are used. Early MS work has focused on thermal desorption of the additives from the bulk polymer, followed by electron impact ionisation (El) [98,100], Cl [100,107] and field ionisation (FI) [100]. These methods are limited in that the polymer additives must be both stable and volatile at the higher temperatures, which is not always the case since many additives are thermally labile. More recently, soft ionisation methods have been applied to the analysis of additives from bulk polymeric material. These ionisation methods include FAB [100] and LD [97,108], which may provide qualitative information with minimal sample pretreatment. A comparison with FAB [97] has shown that LD Fourier transform ion cyclotron resonance (LD-FTTCR) is superior for polymer additive identification by giving less molecular ion fragmentation. While PyGC-MS is a much-used tool for the analysis of rubber compounds (both for the characterisation of the polymer and additives), as shown in Section 2.2, its usefulness for the in situ in-polymer additive analysis is equally acknowledged. 

Resolution does not affect the accuracy of the individual accurate mass measurements when no separation problem exists. When performing accurate mass measurements on a given component in a mixture, it may be necessary to raise the resolution of the mass spectrometer wherever possible. Atomic composition mass spectrometry (AC-MS) is a powerful technique for chemical structure identification or confirmation, which requires double-focusing magnetic, Fourier-transform ion-cyclotron resonance (FTICR) or else ToF-MS spectrometers, and use of a suitable reference material. The most common reference materials for accurate mass measurements are perfluorokerosene (PFK), perfluorotetrabutylamine (PFTBA) and decafluorotriph-enylphosphine (DFTPP). One of the difficulties of high-mass MS is the lack of suitable calibration standards. Reference inlets to the ion source facilitate exact mass measurement. When appropriately calibrated, ToF mass... 

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. 

B magnetic sector E = electric sector Q = quadrupole mass filter ToF = time-of-flight mass spectrometer IT = ion trap FTICR = Fourier-transform ion-cyclotron resonance. 

Fourier-Transform Ion-Cyclotron Resonance Mass Spectrometry... 

B. Asamoto (ed.), FT-ICR/MS Applications of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, VCH Publishers, New York, NY (1991). 

Fourier transform ion cyclotron resonance mass spectrometry... 

CsFeo.72Agi.28Te2,1053 and Cs2Ag2ZrTe4. The latter has a structure that comprises 2D slabs of Ag- and Zr-centered tetrahedral separated by Cs+ cations.1054 Gas-phase silver chalcogenide ions of the type [Ag2 i E ] (E = S, Se, Te) with < 14 have been investigated by laser-ablation Fourier transform ion cyclotron resonance mass spectrometry.1055... 

Currently PCR and mass spectrometry are performed by two separate instruments. However, there is no reason why PCR followed by simple automated cleanup and mass spectrometry cannot be incorporated into a single integrated instrument. Essentially every configuration of the modern ESI mass spectrometer has been used successfully for the analysis of PCR products, from the highest to the lowest resolution involving. Fourier transform ion cyclotron resonance (FTICR), triple quadrupole, quadrupole-time of flight (Q-TOF), and ion trap.22-24 MS discriminates between two structurally related PCR products by MW difference. Mass accuracy is needed to differentiate the... 

Wunschel, D. S. Pasa-Tolic, L. Feng, B. B. Smith, R. D. Electrospray ionization Fourier transform ion cyclotron resonance analysis of large polymerase chain reaction products. J. Am. Soc. Mass Spectrom. 2000,11, 333-337. 

It should be pointed out that FAB, MALDI, and ESI can be used to provide ions for peptide mass maps or for microsequencing and that any kind of ion analyzer can support searches based only on molecular masses. Fragment or sequence ions are provided by instruments that can both select precursor ions and record their fragmentation. Such mass spectrometers include ion traps, Fourier transform ion cyclotron resonance, tandem quadrupole, tandem magnetic sector, several configurations of time-of-flight (TOF) analyzers, and hybrid systems such as quadrupole-TOF and ion trap-TOF analyzers. 

In analyses where molecular masses are being matched, more accurate mass measurements provide more reliable matches and identifications.26,65,66 In a reference laboratory the mass accuracy to several decimal points, provided by a Fourier transform ion cyclotron resonance mass analyzer, may be desirable. In field or portable systems there is usually a trade-off in mass accuracy for size and ruggedness. Reliable identifications can be made with moderate mass accuracy, even 1 Da, if a large enough suite of molecular ions is recorded and used to search the database. If both positive ion and negative ion spectra are... 

Wu, Z. Jernstroem, S. Hughey, C. A. Rodgers, R. R Marshall, A. G. Resolution of 10,000 compositionally distinct components in polar coal extracts by negative-ion electrospray ionization Fourier transform ion cyclotron resonance. Mass Spectrom. Ener. Fuels 2003,17, 946-953. 

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