Ion-trap electrodes

By expanding the circled region in Fig. 13, the ion-trap stability diagram (Fig. 14) plotted in terms of the parameters az and qz is obtained. These parameters are directly related to the RF (qz) and DC (az) voltages applied to the ion-trap electrodes. The areas of stability have boundaries where the (lu parameters (u — z or r) have values 0 and 1. fju is a complex function of au and qu and is directly related to the fundamental secular frequency of the ion (mu) and the main RF frequency (Q) by the equation... 

Ion traps (March and Todd, 2005) have in themselves the possibility of performing all three stages of MS/MS experiment (precursor ion selection, its collision with a target gas, analysis of the product ions) in the same physical space limited by the three-ion trap electrodes (intermediate ring and two end caps). This will operate as a MS/MS in time device. This result is achieved by varying, in a sequential way, the potential applied on the electrodes. 

FIGURE 9.9 (a) Cross-section of the quadrupole ion trap electrodes, (b) A picture of the... 

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 Finnigan ITD-800, that was introduced subsequently, had a separate high temperature vacuum enclosure that contained the ion trap electrodes. The reduction of water and air contamination in the vacuum chamber reduced the Cl content of the mass spectra to a negligible level. However, the use of early XT personal... 

Figure 2.26 Ion trap electrodes. A cross-sectional view of the cylindrically symmetric electrodes from a Finnigan LCQ ion trap is shown. The symmetry axis coincides with the line labelled zq. In the ICP-MS ion trap instruments, ions are injected through a hole in the center of one endcap electrode (left side of figure) and ions are mass-selectively ejected from the opposite endcap electrode where they are detected...

Figure Bl.7.1. Schematic diagram of an electron ionization ion source source block (1) filament (2) trap electrode (3) repeller electrode (4) acceleration region (5) focusing lens (6).

Figure Bl.7.14. Schematic cross-sectional diagram of a quadnipole ion trap mass spectrometer. The distance between the two endcap electrodes is 2zq, while the radius of the ring electrode is (reproduced with pennission of Professor R March, Trent University, Peterborough, ON, Canada).

Potcntiomctric Biosensors Potentiometric electrodes for the analysis of molecules of biochemical importance can be constructed in a fashion similar to that used for gas-sensing electrodes. The most common class of potentiometric biosensors are the so-called enzyme electrodes, in which an enzyme is trapped or immobilized at the surface of an ion-selective electrode. Reaction of the analyte with the enzyme produces a product whose concentration is monitored by the ion-selective electrode. Potentiometric biosensors have also been designed around other biologically active species, including antibodies, bacterial particles, tissue, and hormone receptors. 

A different ion guide is the ion tunnel, which also uses only RF fields to transmit ions. It is not a rod device but consists of a series of concentric circular electrodes. It is perhaps best described as operating like a series of ion traps. This chapter gives details of some of the fundamental characteristics of rod-type transmission guides (multipoles). 

Fig. 3. Schematic diagram of an ion trap where A and B represent end cap electrodes, C the ring electrode, Tq the internal radius of C, and the internal...

The quadrupole ion-trap, usually referred to simply as the ion-trap, is a three-dimensional quadrupole. This type of analyser is shown schematically in Figure 3.5. It consists of a ring electrode with further electrodes, the end-cap electrodes, above and below this. In contrast to the quadrupole, described above, ions, after introduction into the ion-trap, follow a stable (but complex) trajectory, i.e. are trapped, until an RF voltage is applied to the ring electrode. Ions of a particular m/z then become unstable and are directed toward the detector. By varying the RF voltage in a systematic way, a complete mass spectrum may be obtained. 

AFID = alkali-flame ionization detection FID = flame ionization detection FPD = flame photometric detection GC = gas chromatography IGEFET = interdigitated gate electrode field-effect transistor ITMS = ion trap mass spectrometry MIMS = multiphoton ionization mass spectrometry MS = mass spectrometry... 

Sediment Trap in silver nitrate. Potentiometry/ ion-selective electrode No data NR Allen et al. 1994... 

Lindell H, Jappinen P, Savolainen H. 1988. Determination of sulphide in blood with an ion-selective electrode by pre-concentration of trapped sulphide in sodium hydroxide solution. Analyst 113 839-840. 

A three-dimensional ion trap is formed by three electrodes, two end caps and a ring electrode in the linear ion trap different electrodes form each of the four edges (Figure 2.11). 

The ions introduced into the trap are maintained on stable orbits applying DC and RF potential to the electrodes. To separate ions, according to their m/z, a RF scan is made. While the RF amplitude increases, ions with higher m/z values are destabilized and they leave the ion trap moving towards the detector. 

The situation is different for analysis in time (Figure 2.14b). In this case, the three main processes, i.e. ion separation, CID and analysis of product ions, occur inside the same analyzer just changing the forces acting on the ions over time. Hence, in an ion trap, it is possible to isolate the ions of interest, by application of a suitable RF and voltages to its electrodes, to apply a supplementary voltage for CID with the helium present inside it, and to... 

Fig. 17.9 Sketch of a typical setup for ion trap experiments on lasing microdroplets. The oscillating field between the inner and outer ring electrodes forms the trapping potential, and gravitational forces can he opposed by static electrical fields to move the droplet to the trap center with no micromotion...

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