The Ion Trap Analyzers

After this trapping process, ions are measured by changing the voltages applied. Changing the voltages makes the ions to leave the trap (light ones first, heavy ones last) and allows detection. 

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The three-dimensional quadupole field ion trap - or Paul trap is a three-electrode device [see Figure 4.5(b)]. Ions are injected into the device and collected in packets from an ESI or MALDI source. The ion trap analyzer is capable of MS, MS" (MS = MS-MS-MS) and high-resolution scans (R = 20,000). The ion packets enter through an entrance-end cap and are analyzed by scanning the RF amplitude of the ring electrode. The ions are resonated sequentially from low to high m/z and are ejected from the ion trap through the exit-end cap electrode to a detector. Unlike the triple quadrupole (QqQ) mass spectrometer discussed previously, the ion trap performs tandem mass spectrometry (MS-MS) scan modes in the same analyzer. 

Before the GCQ, ion trap mass spectrometers consolidated the processes of ioni2ration and mass analysis inside the ion trap analyzer. Effluent entered the ion trap, where it is bombarded with electrons, and ions are created. Ions at each mass-to-charge could then be ejected by scanning the RF voltage to the end cap of the mass analyzer. 

Two other analyzers now commonly interfaced with GC are shown in Figure 7.8. These include the ion trap analyzer in which ions can be confined by electric and magnetic fields (38-40). Ion traps are essentially three-dimensional quadrupoles. Ions of a specific miz value circulate in stable orbits within the analyzer. A relatively high pressure of helium (10 Torr) is used as a bath gas... 

Instruments are available that can perform MS/MS type experiments using a single analyzer. These instruments trap and manipulate ions in a trapping cell, which also serves as the mass analyzer. The ion trap and fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers are examples. 

The ion trap is one of the most recently introduced analyzers. It is strictly related to the quadrupole mass filter and it uses the same forces of the quadrupole analyzer, i.e. electric... 

Various analyzers have been used to analyze phenolic compounds. The choice of the MS analyzer is influenced by the main objective of the study. The triple quadrupole (QqQ) has been used to quantify, applying multiple reaction monitoring experiments, whereas the ion trap has been used for both identification and structure elucidation of phenolic compounds. Moreover, time-of-flight (TOF) and Fourier-transform ion cyclotron resonance (FT-ICR) are mainly recommended for studies focused on obtaining accurate mass measurements with errors below 5 ppm and sub-ppm errors, respectively (Werner and others 2008). Nowadays, hybrid equipment also exists, including different ionization sources with different analyzers, for instance electrospray or atmospheric pressure chemical ionization with triple quadrupole and time-of-flight (Waridel and others 2001). 

The main MS/MS techniques are precursor ion, product ion, and neutral loss. In addition, it is possible to carry out MSn experiments using an ion trap (Kang and others 2007). In this context, de Rijke and others (2003) carried out a study with 15 flavonoids, comparing different ionization sources and different analyzers. Among the results, the authors showed that the main fragmentations observed in the MS spectra on the ion trap, or the tandem MS spectra on the triple-quadrupole, were generally the same. 

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. 

The ion-trap mass spectrometer uses three electrodes to trap ions in a small volume. The mass analyzer consists of a ring electrode separating two hemispherical electrodes. A mass spectrum is obtained by changing the electrode voltages to eject the ions from the trap. The advantages of the ion-trap mass spectrometer include compact size and the ability to trap and accumulate ions thus increasing the signal-to-noise ratio of a measurement [534,535,551, 553]. 

It is certainly desirable to have at least sufficient resolution to resolve isotopic patterns to their nominal mass contributions. However, not every mass analyzer is capable of doing so with any ion it can pass through. Such conditions often occur when ions of several thousand u are being analyzed by quadrupole, time-of-flight or quadrupole ion trap analyzers, and hence it is useful to know about the changes in spectral appearance and their effect on peak width and detected mass. [42]... 

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). 

The two main types of mass spectrometers used for analysis and detection of explosives are the quadrupole and the ion trap. These two types of mass analyzers are relatively small, when compared with magnetic sector instruments. They can be miniaturized to make mobile detectors weighing less than 15 kg. 

Ion trap/TOF This combination is advantageous because it enables the MS" capabilities of an ion trap with the high mass accuracy and speed of a TOF analyzer. The ion trap can either be a conventional hyperbolic Penning-type device or a linear trap device. Below we describe the deployment of the former type ion trap/TOF for explosives detection. 

Quadrupole ion traps are closely related to quadrupole mass analyzers, but in the ion trap the fields are manipulated so that the ions of interest are trapped, rather than passed through to a detector. Instruments of this type are being investigated for space-flight applications. 

These are not the only types of tandem mass spectrometers. There are numerous configurations of instruments that are based on the type of ion separation and many new terms associated with these instrument types. For example, there are instruments known as ion traps. The ion trap is a device that can measure mass, fragment a selected mass (as could be done in a collision cell) and then measure the mass of the fragment. The product ion produced by this all in one device is the same product ion that would be produced in a tandem quadrupole instrument. However, there is only one mass analyzer that functions as both the collision cell and mass measuring device. These types of instruments are sometimes referred to as tandem mass spectrometers, but are not abbreviated as MS/MS. The MS/MS analysis is done by separating the analysis in time (tandem in time) rather than two devices separated in space. A more generic term is best suited. This term is MS , where the n represents... 

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