Mass analyzers ion-trapping

Different types of mass analyzers have been used for anthocyanin analysis single or triple quadrupole mass analyzers, TOP mass analyzer,ion trap mass analyzers,and the combination of analyzers cited above. " ... 

Traditional detectors (i.e., FID electron capture detector, BCD nitrogen-phosphorous detector, NPD) supply only retention data. However, in many cases this is not enough for proper identification of analytes. Application of GC coupled with an MS detector gives much more information (i.e., the mass spectmm of each compound). GC-MS is a well known and frequently used technique that combines the highly effective separation of GC with the high sensitivity and selectivity of MS. Moreover, improvements in analytical instruments based on different types of mass analyzers (ion trap, quadrupole, and TOF) and the development of hybrid Q-TOF has enhanced the analytical capabilities of modem hardware. Different kinds of mass spectrometers are presented in Table 14.2 [119]. 

Tandem mass spectrometry methods (also abbreviated as MS/MS or MS") are used to characterize individual compounds in mixtures or to determine an individual compound s structure. They are based on the separation of the ions of interest from all other ions, both in space and in time. Separation in space is achieved by coupling two or more mass analyzers, such as BE, EBE, QQ, BEE, etc. Separation in time is achieved using a single mass analyzer (ion trap or ICR), which performs two steps of mass analysis. Once mass separation is completed, various types of experiment can be performed in order to identify the structures of the ions. In a traditional MS/ MS experiment, dissociation products of mass-selected ions are detected. However, different types of experiment, such as the detection of precursor ions for a specific fragment and the identification of ions that have lost a neutral fragment of specific mass, are often available. 

The ion trap mass analyzer is similar to the quadrupole but with the important distinction that it can isolate and trap ions in an electrical field. Notably, the ion trap differs significantly from quadrupoles in design and operation in that triple quadrupoles perform tandem mass analysis on ions as they pass through an analyzer ion traps are capable of isolating and retaining specific ions for fragmentation upon collision with an inert gas in the same cell. An ion trap is about the size of a tennis ball and consists of a donut-shaped electrode and two perforated disk-like end-cap electrodes. 

TD-IT, Thermal desorption-ion trap CAD MIKE, collisionally activated decomposition mass-analyzed ion kinetic energy MID, multiple ion detection FID, flame ionization detector NPD, nitrogen/phosphorus detector SIM, selected ion monitoring El, electron impact TMS, trimethylsilane MTBSTFA, N-methyl-N-(tetr.-butyldimethylsilyl)trifluoroacetamide. 

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. 

All major mass spectral data collections consist of El mass spectra, mostly recorded under accepted standardized conditions such as an ionization voltage of 70 eV, an emission current of 100-200 xA, and an ion source temperature of 150-200°C. Several types of GC/MS systems may be applied, for instance, magnetic sector, quadrupole, or ion trap analyzers. Ion trap systems are considered less applicable, when data comparison is required with spectra from a reference library. In particular, basic compounds related to VX or the three nitrogen mustards tend to produce protonated molecular ions by self-protonation. Magnetic sector and quadrupole mass spectrometers suffer less from interference of self-protonation, and spectra produced with these types of instruments are generally reproducible. 

The RF quadrupole ion trap mass spectrometer (ITMS) is a close relative of the QMF and ideally can be thought of as a three-dimensional quadrupole (see Fig. 17.8). The close relationship of these two devices is evident by the fact that ion motion in the two devices is governed by essentially the same mathematical equations. As with the QMF, the ITMS uses DC and RF electric fields and the operation of the IT is described by solutions to the Mathieu equation. Unlike the QMF, ITMS analyzers trap ions within the mass analyzer. Ions are trapped, ejected to select the mass of interest, and then ejected in a controlled manner for detection. 

Fourier-transform (FT) mass analyzers belong to a special class of mass analyzer that detects ions non-destructively and periodically. Therefore, FT mass analyzers are trapping-type instruments. Because periodic and long detection times facilitate accurate ion recognition, FT mass analyzers offer the highest mass resolving power and accuracy of all instruments [23]. The concept of FT-MS was first described by Comisarow and Marshall in the 1970s [24]. The most important types of FT instruments available in the market include ion cyclotron resonance (ICR) [23] and orbital ion trap (orbitrap) [25] mass analyzers. 

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... 

Ion trap A mass analyzer that traps all ions from a pulse of ionization at the center of a ring and cap electrode structure energized with DC and radio frequency (rf) fields. Ions of different masses are accelerated out of the trap to an external detector by selective addition of energy. 

Commercial mass analyzers are based almost entirely on quadrupoles, magnetic sectors (with or without an added electric sector for high-resolution work), and time-of-flight (TOE) configurations or a combination of these. There are also ion traps and ion cyclotron resonance instruments. These are discussed as single use and combined (hybrid) use. 

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. 

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