Ion-trap dimension

The ion trap used in the experiments and shown in Figure 10.2b has the following dimensions Tq = 3.50 mm, Zq = 2.70 mm, Zendcap = 20.00 mm, andR = 4.00 mm these values have been chosen in order to achieve a nearly perfect radial quadrupole RF field [19] and a near-harmonic DC-axial potential over a few millimeters. Numerical simulations show that these choices of ion-trap dimensions result in ti = 0.248. The applied RF field is coupled resonantly to the ion-trap electrodes at a radial frequency... 

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). 

A vitally important aspect of ion trap operation is the ability to impart translational energy selectively to ions via resonance absorption of alternating current (ac) voltages (10-450 kHz) applied to the endcap. Unlike for linear quadrupole (or other multipole) collision cells, the absorption of energy is m/z specific as each m/z in the trap precesses at a specific set of frequencies, the most important of which for MS/MS is ooz, the fundamental frequency of motion in the z dimension, which is defined by... 

An ion trap is a device that uses an oscillating electric field to store ions. The ion trap works by using an RF quadrupolar field that traps ions in two or three dimensions. Therefore, ion traps can be classified into two types the 3D ion trap or the 2D ion trap. 

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. 

In using the Mathieu equations to locate areas where ions of given masses have a stable trajectory, the equations are very similar to the ones used for the quadrupole. However, in the quadrupole, ion motion resulting from the potentials applied to the rods occurs in two dimensions, x and y, the z motion resulting from the kinetic energy of the ions when they enter the quadrupole field. In the Paul ion trap the motion of the ions under the influence of the applied potentials occurs in three dimensions, x, y and z. However, due to the cylindrical symmetry x2+y2 = r2, it can also be expressed using z, r coordinates (Figure 2.13). 

The operation of the QIT is based on the same physical principle as the quadrupole mass spectrometer described above. Both devices make use of the ability of RF fields to confine ions. However, the RF field of an ion trap is designed to trap ions in three dimensions rather than to allow the ions to pass through as in a QMF, which confines ions in only two dimensions. This difference has a significant unpact on the operation and limitations of the QIT, The physical arrangement of a QIT is different from that of a QMF. If an imaginary axis is drawn through the y-axis of the quadrupole rods, and the rods are rotated around the axis, a solid ring with a hyperbolic inner surface results from the x-axis pair of rods. 

The premise is to utilise a liquid film to provide a reaction environment which can be dynamically controlled in terms of heat and mass flux (influx/effiux) and to complement this with the on-line monitoring technique of Atmospheric Pressure chemical Ionisation (APcI)-Ion Trap Mass Spectrometry (ITMS). This technique allows the flux of protonated molecular ions (Mlf to be directly monitored (mass spectral dimension 1) and to fragment these species under tailored conditions within the ion trap (Collision Induced Dissociation (CID),mass spectral dimension 2), to produce fragment ions representative of the parent ion. This capability is central to allowing species with a common molecular weight to be quantified, for example butan-2,3-dione (MW=86 MH =87, glucose degradation product) and 3-methylbutanal (MW=86 MH =87, Strecker aldehyde from leucine). 

Syagen has developed a prototype portable MS instrument called the FieldMate. It has both electron impact (El) and photoionisation (PI) sources and a quadrupole ion trap, time-of-flight (QitTof) mass analyser. It has MS-MS capability and can be interfaced with a GC (Figures 8.11 and 8.12). It weighs just under 32 kg and its dimensions are 45.7 X 40.6 X 35.6 cm. FieldMate permits direct air and liquid sampling using the PI source. 

Geppert, H. and Kern, H., Ion trap GC-MS/MS determination of chlorinated pesticides in drinking water. An additional dimension with more reliability, GIT Labor Fachzeitschrift, 44(8), 896-897, 2000. 

Dimensions and Operating Parameters for the Quadrupole Ion Trap Used in the Simulations... 

It is not easy to machine traps of such a small design and to retain the ideal hyperboloidal form. In addition, optical beam access becomes very restricted, when the trap size is diminished. Fortunately, millimeter-scale ion traps are well suited to store the particle in a very small volume (that is, of the dimension of the wavelength). In the region close to the center of the device, the conditions to obtain a quasi-pure quadrupole field are not too constraining. The goal consists essentially to realize a small trap, the geometry of which enables the creation of a suitable confinement field, and with a structure sufficiently open to permit illumination of the ion in the trap and efficient collections of photons emitted by the single atom. 

The trapping dimensions in QITs and LITs are essentially simple harmonic oscillators, at least near the center of the traps. Because of this, in addition to trapping fields, ions have their own resonant frequencies inside the trap which can be used to excite them resonantly to high excursion trajectories. At high trajectories, their vibrational activation will cause them to fragment, allowing MS/ MS experiments to be conducted. Resonant excitation is also used to selectively... 

---