Electrostatic ion trap

The orbitrap is an electrostatic ion trap that uses the Fourier transform to obtain mass spectra. This analyser is based on a completely new concept, proposed by Makarov and described in patents in 1996 [26] and 2004 [27], and in Analytical Chemistry in 2000 [28], A third patent describes a complete instrument including an atmospheric pressure source [29], Another article was also published with Cooks in 2005 [30]. The first commercial instrument was introduced on the market by the Thermo Electron Corporation in June 2005. 

Ijames, C.F. A proposed two dimensional quadrupole/electrostatic ion trap time-of-flight mass spectrometer. Proc. 44th ASMS Conference on Mass Spectrometry and Allied Topics, Portland, Oregon, 1996. 

Electrostatic ion trap comprised of a spindle-shaped inner electrode and a split outer electrode ions (from API) rotate around and oscillate along the inner electrode... 

In its most commonly encountered form, the ion trap mass spectrometer is a low-resolution instrument used in dedicated GC— MS systems. Ions introduced into an electrostatic ion trap mass spectrometer perform stable oscillations within a cavity bounded by two hemispherical electrodes and one ring electrode. Ramping the potentials applied to the electrodes causes the oscillations to become unstable and the ions are fiung out of the trap in mass (m/e) order. 

The Orbitrap is an electrostatic ion trap using fast Pourier transformation to obtain mass spectra. Its high mass accuracy (2—5 ppm) and resolving power (adjustable up to 100,000 fwhm) allows discrimination between isobaric interferences and ions of interest, even with a complex background. Plowever, due to the high price of the Orbitrap, there are still not many applications in the field of veterinary residue analysis. 

In the following years, the latter category of m/z analyzers has been combined with both ionization techniques [14], as have been FT-ICR MS (Fig. If), TOF MS in orthogonal configuration, and a series of hybrid instruments that combine a quadrupole MS or electrostatic ion trap with an orthogonal TOF [15-18] (Fig. Id) or FT-ICR analyzer [19-23]. The most recent innovation has been a new electrostatic ion trap design, called or bitrap [24,27], which in combination with an upfront linear ion trap [25,26] provides excellent MS/MS and MS/MS/MS performance, impressive resolving power (> 50 000 FWHM), and a mass accuracy of 0.5-2 ppm for peptides that comes close to what, so far, has only been possible with very expensive FT-ICR MS instrumentation [20,27-29]. This means that for a 1-kDa peptide the expected experimental error is only 0.0005-0.002 Da or 1-4 times the mass of an electron. 

MALDI-TOF MS is by far the fastest and also the most sensitive of all MS techniques available for the analysis of peptides and small proteins, due to the very short analysis times (fractions of a millisecond) and high ion transmission of TOF MS. In addition, it is not limited to the analysis of peptides, as are all currently available combinations of MALDI with FT-ICR MS, electrostatic ion traps, or quadrupole analyzers due to their limited m/z range. This hmitation does not apply to ESI, which in contrast to MALDI delivers large molecules exclusively as highly charged molecular ions. 

As a consequence, for accurate molecular mass analysis of intact proteins, ESI in combination with an orthogonal TOE, electrostatic ion trap or FT-ICR MS is the preferred instrumentation if the samples are very clean and not too complex. If this is not the case or sample throughput is more important than mass accuracy, MALDI-TOF MS is the first choice. Another important advantage of ESI is its superior performance for the analysis of noncovalent complexes including DNA-protein interactions. 

For the mass spectrometric analysis of peptides, the two ionization techniques are similarly complementary as they are for proteins [38]. Today, most mass spectrometers equipped with an ESI or a MALDI source provide the possibility of isolating analyte ions on the basis of their m/z ratio and, by different activation methods, transfer energy to them which results in their decomposition. Mass analysis of the resulting fragment ions can provide detailed structural information and is termed tandem-MS or MS/MS analysis (Fig. 2). Electrostatic ion traps and FT-ICR analyzers also provide multiple stages of ion isolation and fragmentation experiments (MS ), of which MS is especially useful for protein identification and modification analyses. 

These two combinations are currently the most sensitive for MS/MS analyses of peptides. The resolving power and mass accuracy, as well as the control over the fragmentation reactions is, however, significantly lower compared to those of ESI or MALDI combined with hybrid orthogonal TOP, electrostatic ion traps, or FT-ICR MS. 

Magnetic and electrostatic sectors, quadrupole, and time of flight analyzers belong to the first group, while ion trap, Orbitrap and Fourier transform ion cyclotron resonance analyzers separate ions in time. 

The ion trap is a similar analyzer. There are two end cap electrodes that are at ground potential. An electrostatic field is generated hy a donut-shaped hyperbolic electrode within the cap, which maintains ions in a stable trajectory. Changing electrode voltages ejects ions of a particular mass from the trap into the detector (Honour, 2003). 

These ligands are frequently used as metal ion traps to bind undesired metal ions, e. g. in formulations of X-ray contrast agents. Chelated cations may associate electrostatically with anionic compounds and with solvent molecules by weak interactions. This results in the formation of an outer coordination sphere. Instead of the term complex the term chelate is very frequently used meaning that the metal ion is covered by the ligand like a claw ( chela word from the Greek for claw). 

Due to its radically different design, the latest hybrid linear ion trap FTMS instrument, the LTQ-Orbitrap (Fig. 5.6), does not suffer from the time-of-flight effect. In this instrument, the superconducting magnet and the ICR cell are replaced by an electrostatic trap (C-trap) and so distances traveled by the ions from one MS device to the other are much smaller in addition a radically different ion transfer mechanism virtually eliminates any possibility for a time-of-flight effect (Makarov,... 

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... 

No one single mass analyzer is suitable for all applications and the choice of instrument is determined by the type of problem under investigation [68]. Double focusing magnetic/electrostatic sectorfield-, quadrupole-, quadrupole ion trap-, time-... 

A.A. MAKAROV describes a new type of mass analyser the orbitrap. The orbitrap is a high-performance ion trap using an electrostatic quadro-logarithmic field [5,69]. 

Traditionally, ion traps have been divided into three classes QIT, which rely on RF fields to provide ion trapping a linear ion trap, which is closely related to the QIT in its operating principles and ion cyclotron resonance (ICR) mass spectrometers, which rely on a combination of magnetic fields and electrostatic fields for trapping. 

Ramsey and Ramseyalso described microchip interfacing to an ion trap mass spectrometer. Microfluidic delivery was realized by electroosmotically induced pressures and electrostatic spray at the channel terminus was achieved by applying a potential between the microchip and a conductor spaced 3-5 mm from the channel terminus. Tetrabutylammonium iodide was tested as a model compound with this device. Later, Ramsey et reported use of a microchip nanoelectrospray tip coupled to a time-of-flight mass spectrometer for subattomole sensitivity detection of peptides and proteins. A fluid delivery rate of 20-30 nL/min was readily obtained by applying an electrospray voltage to the microchip and the nanospray capillary attached at the end of the microfabricated channel without any pressure assistance. 

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