Octapoles

On the carbons, nitrogens and oxygens expansions up to octapole level were introduced, whereas the expansions were limited to quadrupole level for the hydrogen atoms. All atoms were given a k expansion/contraction parameter for the spherical monopole term, and all atoms except the hydrogens were given k parameters to expand or contract the non-spherical poles. The k and k values on 0(1) and 0(3), on N(l) and N(3), on C(l) and C(3) and on 0(21) and 0(22) were constrained to be equal. 

Fig. 1.8 Di fferential pumping design with heated capilla. This configuration requires a dual stage pumping system before the ions are introduced into the quadrupole mass analyzer which needs to be operated at high vacuum. The role of the lenses is to focus ions. In some systems the lenses are replaced by hexapoles or octapoles.

It is those functions with an inverse sixth-power dependence on the separation that are our main concern in this chapter. Those power laws with exponents greater or less than 6 are included in Table 10.1 mainly to emphasize the point that many types of interactions exist and that these are governed by different relationships. The interactions listed are by no means complete Interactions of quadrupoles, octapoles, and so on might also be included, as well as those due to magnetic moments however, all of these are less important than the interactions listed. Let us now examine Table 10.1 in greater detail. 

Figure 5.6. Schematic of a hybrid LTQ-Orbitrap mass spectrometer (a) transfer octapole (b) curved rf-only quadmpole (C-trap) (c) gate electrode (d) trap electrode (e) ion optics (f) inner orbitrap electrode (g) outer orbitrap electrodes (Makarov et at., 2006a).

Even the lawn format still does not represent the final limit of miniaturization. The one well/one catalyst or one bead/one catalyst strategy, where catalyst identity is spatially coded, can be replaced by in situ synthesis combined with mass spectrometry [48]. The advantage of this strategy is the use of a mass spectrometer for the synthesis, reaction and analysis. The described electrospray ionization procedure helps to avoid the cleavage of chemical bonds, which would falsify the results. The synthesis step does not have to deliver clean and isolated products. Instead, after synthesis, the reactants are first separated by a quadrupole. In a second step, they are further reacted in an octapole and the reaction products are finally isolated in a second quadrupole and analyzed. Figure 3.15 describes the screening process in detail [49],... 

In the octapole the species selected are subjected to further catalytic reactions. 

Collision-Reaction Cells. Perhaps the most exciting development regarding molecular ion removal in ICP-MS is the use of collision or reaction cells, introduced in Sec. 3.1.5. These rf-only quadrupole, hexapole, or octapole cells, typically operated at pressures around 10 mtorr, can provide two benefits The collision cell can be used to reduce the ion kinetic energy and to focus ions toward... 

R. de la Flor St. Remy, M. L. Fernandez Sanchez, A. Sanz-Medel, Determination of essential and toxic total elements in premature human milk by inductively coupled plasma mass spectrometry (ICP-ORC-MS), using an octapole reaction cell, J. Anal. Atom. Spectrom., 19 (2004), 616-622. 

The difference between a DRC and a CC ICP-MS is that a reaction cell uses a Q mass spectrometer with a defined stability region, allowing the rejection of a defined mass region from the ion beam, whereas a CC uses a hexapole or octapole mass spectrometer as an ion guide. DRC have no limit on the gas type used, whereas CCs can only use inert gases or a simple reactive gas such as He or H2. Limits of detection (LoDs) for As are 0.01 ng l-1. However, LoDs can only be achievable with careful control of contamination and minimization of polyatomic interferences. Arsenic LoDs may be improved by the introduction of the element into the ICP-MS in the gaseous form, for example, by formation of ASH3, which markedly improves the LoD as nearly 100 percent of the analyte in solution reaches the mass detector. 

A 3D ion trap with an external ESI source (Finnigan LCQ). Ions produced by the ESI source are focused through a skimmer and octapole lenses to the ion trap. The gating lens is used to limit the number of ions injected in the trap, to avoid space charge effects (see further). 

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