Quadrupole Ion Trap QIT

Although both quadrupoles and quadrupole ion traps are based on the stability of ions in the fields created by the combination of rf and dc voltages, the functionality of the two systems is opposite. In the Q analyzer only ions stable in a specific field are passed to the detector, while the unstable ions are lost. In the QIT analyzer all ions are trapped in a stable trajectory within the cell. Selected mJz values are detected as they are rendered unstable by an applied voltage and are eventually ejected from the trap onto the detector. An obvious advantage of the QIT is that the trapped ions can be maintained inside the cell for extended periods and are therefore available for additional experimentation. 

Ions injected into the trap are held by rf and dc voltages placed on the hyperbolic ring electrode and end caps. 

Ions move in a complex sinusoidal path where there are crossover points. Space-charge effects occur at the crossover points of the ion paths when too many ions are present. 

By changing the voltages progressively, ions with different miz values are ejected sequentially onto the detector, generating spectra. 

CID fragmentation takes place when a specific mIz is isolated in the trap and excited in the presence of a neutral gas, providing MS/MS data. 

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Different mass analysers can be combined with the electrospray ionization source to effect analysis. These include magnetic sector analysers, quadrupole filter (Q), quadrupole ion trap (QIT), time of flight (TOF), and more recently the Fourrier transform ion cyclotron resonance (FTICR) mass analysers. Tandem mass spectrometry can also be effected by combining one or more mass analysers in tandem, as in a triple quadrupole or a QTOF. The first analyzer is usually used as a mass filter to select parent ions that can be fragmented and analyzed by subsequent analysers. 

Figure 2.17. Schematic of a linear quadrupole ion trap (QIT). This type of analyzer consists in principle of a quadrupole analyzer with electrodes at the ends to block ion passage in the z-direction.

The quadrupole ion trap (QIT) creates a three-dimensional RF quadrupole field to store ions within defined boundaries. Its invention goes back to 1953, [103-105] however, it took until the mid-1980s to access the full analytical potential of quad-mpole ion traps. [137-140] The first commercial quadmpole ion traps were incorporated in GC-MS benchtop instruments (Finnigan MAT ITD and ITMS). Electron ionization was effected inside the trap by admitting the GC effluent and a beam of electrons directly into the storage volume of the trap. Later, external ion sources became available, and soon a large number of ionization methods could be... 

The majority of H/D studies that have been reported employ quadrupole ion trap (QIT) instruments due to their ease of use, excellent sensitivity, ability to perform MS/MS experiments, compact size, and low cost. Other reports discuss the use of instruments with higher mass-resolving power such as the hybrid QqTOF instruments [47]. A few groups have utilized FT-ICR mass spectrometry, which offers ultra-high mass-resolving power and improved mass accuracy [48, 49]. 

Since the analytical point of view most of current analytical methods are based on LC-MS/MS, but for some classes of pesticides GC-MS continues being the technique of choice. The use of quadrupole ion trap (QIT) to analyze multiple pesticide residues is limited to several multiclass pesticides in fruit [162], because of the limited number of ions that can be isolated at the same time. For this reason, the use of several time windows is required and this is indeed a strong limitation in practice. The use of hybrid triple quadrupole linear ion trap (QqLlT) mass spectrometer has provided significant contribution to the development of high-sensitive multiresidue analytical methods for pesticide control. An example of application is the method reported by Hernando et al. for the analysis of pesticide residues in olive oil [65]. 

QIT The quadrupole ion trap (QIT) utilizes a cylindrical ring and two end-cap electrodes to create a three-dimensional (3D) quadrupolar field for mass analysis. These instruments are capable of selectively trapping or ejecting ions and are often used for the sequential fragmentation and analysis experiments of product ion MS/MS. Also known as a 3D trap due to the configuration (March, 1997). 

Historically, the first ion traps were 3D ion traps. They were made up of a circular electrode, with two ellipsoid caps on the top and the bottom that creates a 3D quadrupolar field. These traps were also named quadrupole ion traps (QITs). To avoid confusion, this term should not be used but should be replaced preferably with Paul ion trap. The acronym QUISTOR derived from quadrupole ion storage is also largely used but not recommended. 

Relatively new mass analyzers with very high resolution include the quadrupole ion trap (QIT) and the Fourier-transform ion cyclotron resonance (FTICR) instruments. In both analyzers, ions are trapped in a 3D field, and are analyzed once trapped. In Table 15.3, the mass analyzers described here are compared. The combination of MS with other analytical techniques is also very common MS has been widely used following chromatographic separations, for mass analysis. 

Quadrupole Ion Trap. QITs are primarily used as GG or HPLG detectors. They are relatively compact, inexpensive, and versatile instruments, excellent for exploratory studies, structural characterization, and sample identification. They are also used for quantitative analysis, though quantitative analysis is not the best use for these devices. 

Figure 6 Schematic of collision-induced dissociation (CID) in the quadrupole ion trap (QIT) (MS2 experiment). In separate events, ions from the source are accumulated and trapped in the space at the center of the electrodes (a). Ions with a specified m/z value are retained in the trap and all others ejected (b). The specified ions are then collisionally fragmented by axial excitation between the two end caps (c). The resulting product ions are then sequentially ejected to generate the product ion spectrum (d). In an MS3 experiment, one of these product ions may be selectively retained in the trap, excited, and fragmented.

FIGURE 4.5 The five mass spectrometers commonly used for proteomic research, (a) ESI triple-stage quadrupole mass spectrometer (b) ESI quadrupole ion trap (QIT) mass spectrometer (c) MALDI time-of-flight mass spectrometer. 

FIGURE 4.7 ESI-quadrupole ion trap (QIT) high-resolution mass spectrum of interleukin-8 (rat) = 7845.3 amu) infused at 10 pmole/ 1. (a) the amino acid... 

The quadrupole ion trap (QIT) mass spectrometer consists of three hyperbolic-shaped electrodes arranged in a cylindrical geometry (see Fig. 2.14). By considering its axial geometry, we can move from the classical Cartesian coordinates to the polar ones. In fact, each point of the space inside the trap can be defined by the value of its axial (z) and radial (r) coordinates. If a potential U + Vcos cot is applied at the intermediate electrode and the two end caps are grounded, a mathematical treatment analogous to that done for quadrupole mass filter can be employed. In this case, a and q values can be defined again as... 

The mass analyzer is used to separate sample ions. Commonly used analyzers include time-of-flight (TOE), quadrupole (Q), quadrupole ion trap (QIT), and Fourier-transform ion cyclotron resonance (FT-ICR) (9-14). These analyzers provide a wide mass range, high accuracy, and resolution for biomolecular analysis. 

An ion trap is a device where gaseous ions can be formed and/or stored for periods of time, confined by electric and/or magnetic fields. There are two commercial types of ion traps in use in MS, the quadrupole ion trap (QIT) and the ion cyclotron resonance trap (ICR). 

Quadrupole ion trap (QIT) mass analyzers are similar to the quadrupoles already discussed in that trajectories within DC and RF fields are used to differentiate ions according to... 

Ion-trap methods include Fourier transform ion cyclotron resonance MS (FTICR-MS) and quadrupole ion traps (QIT or Paul traps). In these methods, ions are produced in or transferred into a region with appropriate geometry walls and some combination of magnetic fields, DC potentials, and RF potentials that confine the ions on the timescale of seconds to days. FTICR-MS has been particularly popular for the study of organometallic ions in the gas phase. In FTICR-MS, the ions are confined by a magnetic field that constrains the ions to the center of the cell. 

An important configuration of quadrupoles is the triple quadrupole (QqQ), in which there are two analytical quadrupoles (Q) separated by a transmission quadrupole (q). While the predominant use of the QqQ is in quantification, this very versatile format has several scanning modes that enable multiple MS/MS approaches to obtain structural information (Section 3.3.3.1). Extensions of the quadrupole technology are the quadrupole ion trap (QIT) and the more recent linear ion trap (LIT) that has higher ion capacity. The resolutions of these ion traps are similar to those of single quadrupoles. However, an advantage of the traps is the ability to store and manipulate ions prior to their detection, thus enabling MS/MS experiments (Section 2.3.2). 

Once ions have been formed, either outside the mass spectrometer using API methods or within the vacuum system by El, Cl, or MALDI, the ions must be separated according to their m/z ratios. There are several types of mass analyzer with significantly different modes of operation, but all separate ions according to their miz ratios, so that these ratios and their intensities can be recorded by the detector. Current mass analyzers include quadrupole (Q), quadrupole ion traps (QIT, LIT), Fourier transformed based (FT), time-of-flight (TOF), and to a much lesser extent, magnetic field (B). 

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