Hexapole system

H2 has been shown to be effective for the reduction of the intensities of polyatomics (ArO" ", ArH" " for Ca and Fe) in work with dry aerosols, as in laser ablation ICP-MS [620]. It has been shown to be generally useful, as demonstrated by Feld-mann et al. [621] with a hexapole system. Helium was also found to be useful for the dissociation of ArO+ and Ar, the latter interfering in the determination of Se and its species [622]. As shown for a hexapole system, the ion energies also are relevant for the effectiveness of the removal of interferents in He/H2 filled cells [623]. Apart from a hexapole, octapole collision cells have also been used, where H2 addition was found to be effective for Ar, ArO, and Ax reduction, and He for ArO+ reduction, but not for ArH or ArJ reduction [624]. In their work on laser ablation ICP-MS, Hattendorf and Gunther also mentioned that Ne was useful as a... 

The hexapole cannot act as a mass filter by applying a DC field and is used only in its all-RF mode, in which it allows all ions in a beam to pass through, whatever their m/z values. In doing so, the ion beam is constrained, so it leaves the hexapole as a narrow beam. This constraint is important because the ion beam from the inlet system tends to spread due to mutual ion repulsion and collision with residual air and solvent molecules. By injecting this divergent beam into a hexapole unit, it can be refocused. At the same time, vacuum pumps reduce the background pressure to about 10 mbar (Figure 22.1). The pressure needed in the TOF analyzer is about 10 ... 

The term Q/TOF is used to describe a type of hybrid mass spectrometer system in which a quadrupole analyzer (Q) is used in conjunction with a time-of-flight analyzer (TOP). The use of two analyzers together (hybridized) provides distinct advantages that cannot be achieved by either analyzer individually. In the Q/TOF, the quadrupole is used in one of two modes to select the ions to be examined, and the TOF analyzer measures the actual mass spectrum. Hexapole assemblies are also used to help collimate the ion beams. The hybrid orthogonal Q/TOF instrument is illustrated in Figure 23.1. 

The octopole configuration is similar to the quadrupole and hexapole in affording a good ion guidance system in its all-RF mode. The poles are connected in two pairs of four nonadjacent rods, and each pair is connected to an RF voltage supply, 180° out of phase with each other. The octopole is even more efficient than the hexapole as an ion guide. 

The gas pressure in the first hexapole section is influenced by gas leaking in from the inlet system and, at about 10" mbar, is higher than desirable if excessive ion/neutral collisions are to be prevented. Therefore, the first hexapole is separated from the second hexapole section by a small orifice, which allows ions to pass through. 

An example of a serial-recording EEL spectrometer is shown in Eig. 2.33 it features a magnetic prism system which was constructed for a TEM/STEM of the type JEOL JEM lOOS [2.199, 2.200]. Its second-order aberrations are corrected by curved pole-piece boundaries, an additional field clamp, and two extra hexapoles acting as stig-mators. The electron beam can be adjusted relative to the optical axis by use of several deflection coils. A magnetic round lens is positioned just in front of the prism to... 

ToFs can also be used in combination with other mass analysers. Both hybrid sector and quadrupole systems are available. oaToF-MS has been interfaced to a quadrupole mass filter and hexapole gas collision cell, such as to allow recording of mass spectra and product ion spectra with good mass resolution (ca. 10000), high sensitivity, high mass range (ca. 10 000 Da) and high mass accuracy (<5ppm) [177,178]. QqToFMS may be fitted with API sources with flow-rates from nL... 

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.

In addition to these collision/reaction cell instruments, since 2002 Thermo Fisher Scientific has been selling the XSeries ICP-MS with a hexapole collision cell (developed from ThermoElemental PQExel ICP-MS) as a bench top instrument on the analytical market. A special ion extraction system in Thermo s XSeries", ion optics together with a hexapole collision cell to minimize the interference problem in ICP-MS, provides the lowest background signals for ICP-QMS (< 0.5 cps). 

The collimated (focused) ion beam leaves the hexapole and enters the ion gating system—the push and pull electrodes (Fig. 27). It is this system which provides the pulse of ions necessary for TOF analysis. When the region in front of the push electrode is filled by the ion beam, the ions are pushed towards the extraction electrodes. As this packet of ions leaves the gate it is reopened and another packet is admitted. At the extraction electrodes, ions are accelerated... 

Figure 5 Schematic for the Micromass hexapole lens system.

Micromass has applied this new hexapole technology to a fast scanning magnetic sector multiple-collector instrument (Fig. 8.6). The source is at ground potential so most of the lens system and analyzer float at —6 kV. The ions are extracted into the hexapole through a sample cone with a 1.1-mm orifice, a 0.8-mm orifice skimmer cone, and finally a 2-mm orifice transfer lens held at —400 V. The hexapole is inclined to prevent line-of-sight transmission and damage to the detectors from the source. A lens system transfers the ions into the mass analyzer. 

Previous studies of aligned and oriented gas-phase reactions had relied on the use of laboratory-based fields (lasers, hexapoles, etc.) to fix reactants relative to the lab system, thereby introducing geometric bias into the reaction [11-20]. However, referring to Figure 1, when a weakly bonded complex is used as a precursor, one of the reactants is encapsulated within one... 

An RF-only hexapole is used in systems from Waters (Figure 5.7). In more recent Waters systems, it is replaced by an ion-tunnel device (see below). 

Figure 2 - The upper panel shows a global view of the apparatus, where the hexapole honeycomb electrode is installed. The geometry of the field and a perspective look of the road system to generate it are also shown. Further details can be found in Ref. [2].

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