Resolution ion trap

Williams, J.D. Cox, K.A. Schwartz, J.C. Cooks, R.G. ch 1, High Mass, High Resolution Ion Trap Mass Spectrometry, Vol. 2, Ion Trap Instrumentation, in Practical Aspects of Ion Trap Mass Spectrometry, R.E. March and J.F.J. Todd, (Eds.), CRC Press, Boca... 

Characterization of this type of lipid classes and molecular species as well as novel lipid classes with multistage tandem MS was also conducted by using a high-resolution ion trap-Orbitrap mass spectrometer [33]. Any readers who are interested in understanding the fragmentation features of these complex lipids (particularly those novel ones) with high-resolution mass spectrometry should consult the paper. 

The molecular constants that describe the stnicture of a molecule can be measured using many optical teclmiques described in section A3.5.1 as long as the resolution is sufficient to separate the rovibrational states [110. 111 and 112]. Absorption spectroscopy is difficult with ions in the gas phase, hence many ion species have been first studied by matrix isolation methods [113], in which the IR spectrum is observed for ions trapped witliin a frozen noble gas on a liquid-helium cooled surface. The measured frequencies may be shifted as much as 1 % from gas phase values because of the weak interaction witli the matrix. 

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. 

Although ion transmission guides and ion traps both use the same universal physical laws to achieve control over ion behavior, the ways in which the laws are used are different, as are the objectives. The guides do not retain ions to gain control over their velocities and are used simply to transmit both slow and fast ions over a very wide range of gas pressures. Ion traps retain ions over a relatively long period of time so as to adjust their kinetic energies and thereby improve mass resolution. The so-called bath gas is used at carefully controlled pressures. 

This focusing action gives an ion beam, in which the m/z values can be measured so accurately that the resolution of a magnetic/electric-sector instrument (separation of ions of different m/z values) is measured as a few parts per million, compared to the more modest few parts per thousand in, say, a quadmpole or ion-trap instrument. 

A. J. H. Eouter, J. van Door-nmalen, J. J. Vreuls and U. A. Th Brinkman, On-line solid-phase extr-action-thermal desorption-gas chr-omatography with ion trap detection tandem mass spectr-ometr-y for the analysis of microcontaminants in water , 7. High Resolut. Chromatogr. 19 679-685(1996). 

Specificity is unsurpassed. Traditionally, MS was performed on very large and expensive high-resolution sector instruments operated by experienced specialists. The introduction of low-resolution (1 amu), low-cost, bench-top mass spectrometers in the early 1980s provided analysts with a robust analytical tool with a more universal range of application. Two types of bench-top mass spectrometers have predominated the quadrupole or mass-selective detector (MSD) and the ion-trap detector (ITD). These instruments do not have to be operated by specialists and can be utilized routinely by residue analysts after limited training. The MSD is normally operated in the SIM mode to increase detection sensitivity, whereas the ITD is more suited to operate in the full-scan mode, as little or no increase in sensitivity is gained by using SIM. Both MSDs and ITDs are widely used in many laboratories for pesticide residue analyses, and the preferred choice of instrument can only be made after assessment of the performance for a particular application. 

Rapid scanning mass spectrometers providing unit resolution are routinely used as chroaatographic detectors. Ion separation is accomplished using either a magnetic sector, quadrupole filter or ion trap device. Ions can also be separated by time-of-flight or ion cyclotron resonance mass analyzers but these devices are not widely used with chromatograidiic inlets and will not be discussed here [20]. 

Tables 6.27 and 6.31 show the main characteristics of ToF-MS. ToF-MS shows an optimum combination of resolution and sensitivity. ToF-MS instruments provide up to 40000 spectra s-1, a mass range exceeding 100000 (in principle unlimited), a resolution of 5000, and peak widths as short as 200 ms. This is better than quadruples and most ion traps can handle. Unlike the quadrupole-type instrument, the detector is detecting every introduced ion (high duty factor). This leads to a 20- to 100-times increase in sensitivity, compared to QMS used in scan mode. The mass range increases quadratically with the time range that is recorded. Only the ion source and detector impose the limits on the mass range. Mass accuracy in ToF-MS is sufficient to gain access to the elemental composition of a molecule. A single point is sufficient for the mass calibration of the instrument. ToF mass spectra are commonly calibrated using two known species, aluminium (27 Da) and coronene (300 Da). ToF is well established in combination with quite different ion sources like in SIMS, MALDI and ESI.

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]. 

Figure 7.32 shows the identification of an oxidation product of Irganox 1330 by means of APCI-MS. LC-APCI-MS/MS (high-resolution sector field-ion trap hybrid) has also been used for the analysis (elemental composition and structure) of Irganox PS 802 [636]. 

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... 

Chien, B. M. Michael, S. M. Fubman, D. M. Enhancement of resolution in matrix-assisted laser desorption using an ion-trap storage/reflectron time-of-flight mass spectrometer. Rapid Comm. Mass Spectrom. 1993, 7,837-843. 

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