3D Quadrupole ion trap

Fig. 11.10. Diagram illustrating the inner surfaces of the primary components of a Paul (3D) quadrupole ion trap. Ions generated by an external source are injected into the trap through an aperture in one of the end caps. Scan functions for isolating ions in the trap, exciting the mass selected ions to induce unimolecular dissociation, and ejecting ions from the trap (for detection) are implemented through the application of DC and RF voltages to the ring electrode.

Fig. 11.11. The stability diagram for a 3D quadrupole ion trap. The area enclosed within the boundaries (shaded gray) represents solutions to the Mat-hieu equations that result in stable trajectories for ions within the trap. The area outside the boundaries represents solutions for the equations that produce unstable trajectories.

Perhaps the simplest mass analyzer of all, the TOF mass spectrometer [46] has experienced a reemergence in the past several years. Like the 3D quadrupole ion trap, the TOF analyzer has come to commercial prominence several decades after its initial introduction. The limitations of electronic components in the 1960s constrained the capabilities of the instrument, limiting its mass range and resolving power. The TOF analyzer operates in a pulsed mode, requiring either a pulsed ion... 

The two-dimensional (2-D) or linear ion trap (LIT) emerged in the 2000s as an effective alternative to the 3-D trap. Before 1995, linear traps were used primarily as ion storage/transfer/ion-molecule reaction devices in combination with FTICR (Senko et al., 1997 Belov et al., 2001), TOF (Collings et al., 2001), 3D ion trap (Cha et al., 2000), and triple-quadrupole (Dolnikowski et al., 1988) mass spectrometers because LITs offer better ion storage efficiencies in comparison to 3D quadrupole ion traps of the same dimensions (Hager, 2002 Schwartz et al., 2002). In 2002, commercial LITs were introduced as either stand-alone mass spectrometers (Schwartz et al., 2002) or as part of a triple quadrupole mass spectrometer (Hager, 2002). 

Traditional 3D quadrupole ion traps utilize three electrodes two end caps and a ring electrode. The end caps are usually at ground potential and a RF voltage is applied to the ring electrode to generate a quadmpole field to store ions. Helium gas is present in the trap at a pressure of 1 mtorr to cool the ions and improve... 

The 3D quadrupole ion trap suffers from a severe limitation. If the number of trapped ions is too high, the electrical field due to the Vcos iot potential is overlapped by that due to the ion cloud. The result is a drop in instrumental performances, particularly in mass resolution and linear response. To avoid this undesired phenomenon, a preliminary scan (not seen by the ion trap user) is performed and the ionization time (or the ion injection time) is optimized, thus confining the optimum number of ions inside the trap (see Fig. 2.18). This prescan leads to a well-controlled instrumental setup but, of course, it limits the sensitivity of the instrument. To overcome this problem, two different approaches can be employed (1) increase the ion storage capacity of the trap by increasing the electric field strength (2) increase the inner volume of the trap, so as to obtain a less dense ion cloud, which results in a decrease of space charge effects. 

Obviously, the resolution of the mass spectra is not sufficient to discern the exact number of H/D exchanges. This particular series of mass spectra were used to correlate observations in the gas phase with similar ones obtained in solution, indicating that ubiquitin may have some memory of the solution conformation even after it is transferred to the gas phase via ESI. Similar results have been reported for studies utilizing a 3D quadrupole ion trap and CD3OD as the deuterating reagent [12]. 

FIGURE 14.1 Diagram of the first 3D quadrupole ion trap instrument designed for the... 

The quadrupole mass filter and the 3D quadrupole ion trap were invented simultaneously by Paul and Steinwedel, who received a patent for these two... 

Volume rv is entitled Theory and Instrumentation and is composed of six parts Fundamentals, New Ion Trapping Techniques, Fourier Transform Mass Spectrometry, Quadrupole Rod Sets, 3D-Quadrupole Ion Trap Mass Spectrometry, and Photochemistry of Trapped Ions. 

In this study, the level of scrambling at different CID fragmentation amplitudes was monitored in the model peptide PI (HHHHHHIIKIIK) with a regioselective deuterium labeling that is a sensitive probe for H/D scrambling (see Section 8.2.3) [43]. In a 3D quadrupole ion trap instrument, the triply charged peptide was subjected to various degrees of RF-induced collisional activation followed by... 

Ion Trap The first demonstration of full-scan MS/MS data for MALDI imaging was obtained with a three-dimesional (3D) quadrupole ion trap (QIT) (Troendle et al., 1999 Garrett et al., 2005). These experiments were performed on an instrument constructed at the University of Florida and clearly demonstrated the critical role of MS/MS for imaging small molecules in tissue. The use of ion traps for MSI has been reviewed (Garrett and Yost, 2009). The QIT can trap and store ions from a pulsed laser desorption event in contrast, quadrupole mass spectrometers and other scanning instruments are... 

A cylindrical ion trap, CIT, configured as the inscribed cylinder to a 3D quadrupole ion trap is shown in Figure 6. A CIT can be fabricated readily from a polished metal cylinder with an internal radius of a few millimeters and two disks perforated for admission of electrons or ions and for ejection of ions. 

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. 

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... 

Recently, O Harr also modified a 3D quadrupole ion trap mass spectrometer equipped with an ESI ion source as a complete chemical laboratory for fundamental gas-phase studies of metal-mediated chemistry. Resolving to the multistage capabilities of the quadrupole ion trap mass spectrometer for collision-induced dissociation and ion/molecule reactions, metal-mediated chemistry relevant to catalysis, C C bond coupling, bioinorganic, and supramolecular chemistry were examined [310]. 

O Hair RA. The 3D quadrupole ion trap mass spectrometer as a complete chemical laboratory for fundamental gas-phase studies of metal mediated chemistry. Chem Commun (Camb). 2006 14 1469-81. 

In the 3D quadrupole ion trap mass analyzer, radiofrequency (RF) voltages are applied to the ring electrode while the end-cap electrodes are typically kept at ground potential. Thus, ions with m/z above a selected value will be trapped inside the mass analyzer, while a continual increase in the RF ampHtude applied to the ring electrode will result in the ejection of ions that pass through an opening in one of the endions with a smaller m/z value will be ejected and detected first [118]. 

D quadrupole ion trap Extremely compact, fast scanning, unit mass resolution, option for MS" experiments ... 

The mass analyser described in the preceding section is sometimes referred to as a linear quadrupole, since the electrodes consist of parallel rods. Another type of mass spectrometer based on the use of a quadrupolar electric field is the three-dimensional (3D) quadrupole ion trap, which is sometimes also known as a Paul trap. This is a device that has been in existence for several decades, but it is only in the past twenty years or so that it has moved from a small number of research laboratories out into the commercial domain. Ion traps are now popular devices for a whole range of mass spectrometry applications, their popularity being enhanced by their very compact size and the ease with which they can be used in MS experiments (see Section 3.5.3.2). Several PTR-MS instruments have been constructed with a quadrupole ion trap and so a description of the basic operating principles... 

An alternative to the 3D quadrupole ion trap (Paul trap) is the linear quadrupole ion trap. The linear ion trap is akin to a hybrid of the quadrupole mass filter and the 3D ion trap in that it consists of a four-rod assembly, like the quadrupole filter, but also it has entrance and end electrodes like the 3D ion trap. Confinement of ions along the axial direction is provided by DC potentials applied to the end electrodes. The quadrupole rods produce radial motion of the ions through application of an RF electric field, in a similar manner to that already described for the quadrupole mass filter. To record a mass spectrum axial ion ejection, initiated by RF excitation, can be used in a procedure similar to that used for the 3D ion trap. 

Three-dimensional ion traps have problems with both poor ion collection efficiencies and space-charge effects, where the latter provides an upper limit on the number of ions that can be stored within the trap. The much larger spatial volume within a linear ion trap reduces the space-charge problem and therefore a larger quantity of ions can be stored in this trap when compared to the 3D quadrupole ion trap. 

---