Octapole guide

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. 

Another important application of a linear quadrapole is operation in the RF-only mode, i.e., where the DC voltage is zero. In this mode, all ions with m/z between a low-mass and high-mass cut-off are transmitted. RF-only quadrapoles (or hexapole or octapole) are used as an ion guide between API sources and mass analysers (Ch. 5.4.5) and as collision cells in various MS-MS instruments. 

R.D. Voyksner, FI. Lee, Investigating the use of an octapole ion guide for ion storage and higf-pass mass filtering to improve quantitative performance of ESI ion-trap MS, Rapid Commun. Mass Spectrom., 13 (1999) 1427. 

An electrodynamic ion furmel interface, positioned between the outlet of a heated stainless-steel capillary and an RF-only octapole ion guide, thus replacing the skimmer, was described by Shaffer et al. [41-42]. The ion furmel interface consists of a series of ring electrodes with decreasing internal diameter. Both RF and DC voltages are apphed to these electrodes. The device provides a more effective focussing and ion transmission. Abont ten-fold sensitivity improvement over a conventional nozzle-skimmer system was demonstrated. 

With the exception of the alkali-metal source, the experimental setup for this work is the same as described previously [12,13]. Alkali-metal ions are generated by surface ionization on a hot filament [14]. The nascent M beam is collected by a radio-frequency (rf) octapole ion guide, then accelerated and mass filtered by a magnetic sector. The mass-selected M beam is then de-... 

It should also be noted that the RF-only quadrupoles (as well as the related RF-only hexapoles and octapoles) can be operated as ion lenses, often referred to as RF-only ion guides or simply ion guides. RF-only quadrupoles (denoted as lower case q , nonitalicized, to distinguish them from the closely related quadrupole mass filters Q) also act as efficient collision cells for collision induced dissociation in triple quadrupole analyzers (QqQ, Section 6.4.3) and hybrid tandem quadrupole-time of flight instruments (QqTOF, Section 6.4.7). Discussion of these devices must be postponed imtil the principles of all hnear quadrupoles have been considered (Section 6.4.2). 

Figure 6.29 A linear quadrupole ion trap for use as a mass spectrometer using radial ion ejection. Top schematic of the trap showing the ejection slot along the length of one of the x-rods. Bottom an overall view of the complete instrument showing typical potentials and pressures. The first (square) quadrupole is an ion guide to transport ions from the ESI source into the higher vacuum region and the function of the small octapole is similar but to facilitate ion transfer into the trap. Reprinted by permission of Elsevier from A Two - Dimensional Quodrupole Ion Trap. .. , by Schwartz, et al. Journal of the American Society for Mass Spectrometry, 13, p. 659-669, 2002, Eig 1, p. 660 Eig 5, p. 662, by the American Society for Mass Spectrometry.

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