Orbital trap mass spectromete

Orbital trapping mass spectrometers achieve resolutions of up to 105 and would be the next choice after ToF mass spectrometers if resolving powers above 104 are required. In addition to mass resolution, the selectivity of an MS can be critical to distinguish between co-eluting and not mass-resolved compounds. For example, typical triple-quad mass spectrometers usually cannot achieve better than unit-mass resolution. However, special operation modes like neutral loss scans and precursor ion scans can filter out compounds of interest even if neither LC separations nor MS scans would be sufficient to resolve these compounds (note that this is a filtering step). 

Besides TOP instruments, other mass analyzers such as quadrapole-orthogonal TOP instruments, ion traps, Pourier transform (PT) ion cyclotron resonance mass spectrometers and, most recently, orbital trapping mass spectrometers were employed for MALDI imaging in microprobe mode, as described later in this chapter (see also Chapter 2). 

Figure 4.10 High-resolution atmospheric pressure-MALDI images of a mouse urinary bladder tissue section, obtained on an orbital trapping mass spectrometer with 10pm step size. Two phospholipid signals closely neighboring in mass were imaged showing...

The principles behind an ion trap mass spectrometer are similar to those of the quadrupole mass filter, except that the quadrupole field is generated within a three-dimensional cell using a ring electrode and no filtering of the ions occurs. All of the steps involved in the generation and analysis of the ions take place within the cell, and in order to detect the ions they must be destabilized from their orbits, by altering the electric fields, so... 

An entirely new principle of the ion-trap mass spectrometers is the Orbitrap with a coaxial inner spindle-shaped electrode in an outer barrel-like electrode. The peripheral injected ions move due to their electrostatic attraction to the inner electrode on orbits around and swing simultaneously along the electrode. The frequency of these harmonic oscillations is inversely proportional to the square root of mJz. The detected signals are induced by the frequency of these swings and resulted... 

Figure B 1.7.18(a) shows a typical FT-ICR mass spectrometer cubic trapping cell. The principal axes are shown in the diagram, along with the direction of the imposed magnetic field. To understand the trajectory of an ion in such a field, the electrostatic and magnetic forces acting on the ion must be described [45]. If only a magnetic field is present, the field acts on the ions such that they take up circular orbits with a frequency defined by the ion mass ...

Only a few applications of orbital-trap (orbitrap) high-resolution mass spectrometers have been reported for STA or GUS so far. For the detection of 29 doping agents, an LTQ-orbitrap mass spectrometer equipped with an APCI ion source was used with insource CID and acquisition in the positive ionization scan mode from 100 to 500 Da (35). The mass resolution of60,000 fiill width at half maximum (FWHM) ensured a precision better than 2 ppm (using external calibration), while the limit of detection was better... 

The development of stable frequency generators have enabled very high resolving power to be claimed for this type of spectrometer. However accurate mass measurement usually requires the addition of an internal standard. This is caused by the problem of coulombic repulsion between ions in the orbit increasing the number of ions within the trap causes slight deviations in the orbital trajectory which is reflected as a small mass shift. 

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