2D Quadrupole ion trap

With the development of the 2D quadrupole ion trap (linear ion trap or LIT) [19,20], the application to tissne specimens was explored farther dne to the increased storage capacity, increased injection efficiencies, and increased trapping efficiencies the use of higher MALDl pressures for tissue samples was explored also. The instrument employed for most of the discussion following was described in detail in a recent publication [4]. A diagram of this instrument is shown in Fignre 14.2. Briefly, the instrument is a linear ion trap fitted with a MALDl ion sonrce that operates... 

A third type of MS/MS instruments is a hybrid of tandem-in-space and tandem-in-time devices, including the Q-trap (QQ-2D-linear trap) [45] and the ion trap-FT-ICR (2D-linear ion trap-FT-ICR) [46]. The Q-trap takes the configuration of triple quadrupole, with the third quadrupole replaced by a 2D-linear ion trap. The uniqueness of this design is that the 2D-linear ion trap component can be used to perform either (a) a normal quadrupole scan function in the RF/DC mode or (b) a trap scan function by applying the RF potential to the quadrupole. It is well-suited for both qualitative and quantitative studies. In the case of ion Trap-FT-ICR, it combines ion accumulation and MS" features of a 2D-linear ion trap with excellent mass analysis capability (mass resolution, mass accuracy, and sensitivity) of FT-ICR. 

The methods for each study are divided into the initial protein separation step, a second separation step if applicable, the type of mass analysis, and the software used for peptide identification. ID = one dimensional polyacrylamide gel electrophoresis, 2D = two dimensional polyacrylamide gel electrophoresis, MS = mass spectrometry (peptide mass fingerprinting), MS/MS = tandem mass spectrometry, MALDI-TOF = matrix assisted laser desorption/ionization-time of flight, MS FIT = software from Protein Prospector, http //prospector.ucsf edu/, ESI = electrospray ionization, Q-TOF = quadrupole-time of flight, PPSS2 =Protana s Proteomic Software Suite (ProtanaEngineering, Odense, Denmark), Mascot = Matiix Science, http //www.matrixscience.com/, TOF-TOF = MALDI plus TOF tandem mass spectrometry, RP-HPLC = reverse phase high performance liquid chromatography, Q-IT = quadrupole ion trap, LIT = linear ion trap. Bioworks = Thermo Electron Corporation. 

Quadrupole mass filters are one of the most common and cost effective mass analyzers. Although they have limited mass resolution (Table 10.2) and are less sensitive than other mass analyzers, they are durable and suitable for high-throughput analyses. To perform a tandem mass analysis (MS/MS), a triple quadrupole MS is used in which three quadrupoles are placed in series to select, fragment, and analyze ions of interest. Quadrupole ion-trapping devices such as linear 2D ion traps are... 

Quadrupole ion traps are now available in two geometries, the recently introduced 2D linear ion trap and the (now classical) 3D quadrupole ion trap (Paul trap). The operating principles of 3D ion traps are closely related to those of the quadrupole mass filter but are considerably more complex and thus demand more space for explanation. However, they are discussed here in some detail both because of their popularity and because the basic principles underlying their operation are shared by... 

The preceding comments were made with no detailed justifications. These can only be made via a reasonably detailed consideration of the fundamental principles underlying operation of 3D quadrupole ion traps. The limitations outlined above were in fact the motivation behind the recent development of the newer 2D ion traps. The remainder of this section attempts to provide a description of these fundamental principles at a level that at least permits an understanding of the strengths and limitations of ion traps in chemical analysis, particularly when compared with triple quadrupoles in the context of trace level quantitation. 

Key among these are quadrupole based instruments, single quadrupoles and triple quadrupoles as well as the closely related quadrupole ion trap instruments (3D and 2D ion traps). Their widespread use in trace quantitative analyses has been facilitated by the fact that these instruments can also be readily coupled to GC and/or LC because of inherent features of the mass analyzer fields, i.e. they operate at or near ground potential. 

D quadrupole ion traps and 2D linear quadrupole ion traps are closely related in operating principles to quadrupoles and as such share many of the same performance features, such as unit mass resolution and nearground potentials that allow facile coupling to both GC... 

LIT The linear ion trap (LIT) (also referred to as a two-dimensional, or 2D, trap) is a variation on the transmission quadrupole mass analyzer. In the LIT, the quadmpole is constructed such that either ions can be analyzed immediately or, ions can be trapped and held in the quadrupole region and then analyzed (Hager, 2002 Schwartz et al., 2002). Various types of MS/MS can be performed, as described in Chapter 3. 

The quadrupole analyser is a device which uses the stability of the trajectories in oscillating electric fields to separate ions according to their m/z ratios. The 2D or 3D ion traps are based on the same principle. 

Besides 3D ion traps, 2D ion traps have also been developed. They are based on a four-rod quadrupole ending in lenses that reflect ions forwards and backwards in that quadrupole. Therefore, in these 2D ion traps, which are also known as LITs, ions are confined in the radial dimension by means of a quadrupolar field and in the axial dimension by means of an electric field at the ends of the trap. 

Many similar applications of quadrupole linear ion trap instruments have been reported [320-322,329,330], As discussed above, the Q-Trap is a triple quadrupole mass spectrometer capable of performing QMF type and 2D ion trapping experiments. This mass spectrometer can be operated exclusively in the QMF mode, as with a conventional QMF, or it can be operated exclusively in the ion trapping mode similar to a conventional 2D ion trap mass spectrometer. Advantages of using a Q-Trap mass spectrometer over a conventional QMF mass spectrometer come into play when one is attempting to perform both quantitative and qualitative metabolite detection/identification experiments from a single injection rather than separate... 

In the operation of 2D and 3D quadrupole instruments, the modification of ion trajectories by ion/ neutral collisions must be considered. In rf quadrupole fields, an ion/neutral collision reduces both ion kinetic energy and ion excursions such that the ions are cooled and focused to the center of each field. Collisional cooling is an important aspect of the behavior of ions in a quadrupole field for example, in a 2D quadrupole device, collisional cooling is employed to limit the excursions of ions so as to form a tightly focused ion beam of diminished kinetic energy constrained close to the central axis. A focused beam of ions may be transmitted through a relatively small orifice from one section of an instrument to the next such that pumping requirements are reduced, and a focused ion beam can be accelerated with reduced ion loss. When the axial motion of a focused ion beam is arrested within a rod array such that the confined ions can be excited resonantly, a linear ion quadrupole trap is obtained. 

Finally in this section, it is noted that single quadrupole mass filters (as opposed to triple quadrupole instruments) are generally used in trace quantitative analyses only for GC-EI(CI)-MS methods for thermally stable analytes (e.g. pesticides in various matrices) in SIM mode. (It is interesting that GC/MS instruments still appear to account for a large fraction of mass spectrometer units sold worldwide.) The same linear quadrupole devices can also be operated as 2D ion trap mass spectrometers, discussed in Sections 6.4.5 and 6.4.6. 

Quadrupole mass spectrometry (Q-MS) has wide functionality making it the most popular form of MS. The family of quadrupole mass analyzers includes a variety of devices, such as quadrupole mass filter (QMF), two-dimensional (2D) ion trap (IT) or linear ion trap (LIT), and three-dimensional (3D) IT. The 3D IT device is also called the Paul trap in honor... 

The 2D- and 3D-Quadrupole Field Ion Trap (QIT) Scan Functions and Timing... 

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