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RF-only quadrupole Q0

Exhibit no. 572

RF-only multipole ion guides can be used for transporting ions from one part of a vacuum system to another in a differentially pumped system. They consist of metal rods arranged symmetrically around a central axis. The rods are separated into two pairs, alternating in such a way that each rod is neighbored by rods of the other pair. The high-frequency voltage is applied to one set of rods, while the same but phase-opposite voltage is applied to the other set of rods. RF-only multipole ion guides are typically used in higher-pressure regions (1 Torr - 1 mTorr), where ions undergo regular collisions.  Reducing kinetic energy makes it easier for the ion guide to focus the ion beam. Quadrupole guides consisting of four rods are commonly used in mass spectrometry. The effective potential produced by RF moves ions to the centerline therefore significantly reducing ion losses.

The exhibit is an RF-only Q0 quadrupole from a triple quadrupole API 4000 manufactured by AB Sciex in 2001. The Q0 RF-only quadrupole consisting of four cylindrical electrodes (rods) was located between the vacuum interface and the front bulkhead on the mass filter rail. The Q0 region was maintained at 8 x 10-3 torr by a turbo pump, backed by a roughing pump. Ions entering the ion path were first focused by the Q0 quadrupole before passing into the Q1. The RF voltage applied to Q0 was a consistent fraction of the RF voltage applied to Q1. The RF-only Q0 also promoted further removal of remaining gas and vapor. Regular cleaning of Q0 was recommended to prevent dramatic loss of the instrument sensitivity.

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