Radio frequency quadrupole

Thomson, B.A. 1997 McBryde Medal Award Lecture Radio Frequency Quadrupole Ion Guides in Modem Mass Spectrometry. Can. J. Chem. 1998, 76, 499-505. 

Quadrupole mass analyzers consist of four rods that produce a radio frequency quadrupole field. Only a single mass-to-charge ratio has a stable trajectory through the mass analyzer, but the electric potentials can be swept rapidly, either continuously or in discrete steps to measure a variety of masses. Quadrupole mass spectrometers are used in a wide variety of applications, but are not widely used in cosmochemistry. 

Ion lifetimes as long as milliseconds have been measured in a number of different ways. One of the earliest methods involved flight tubes some metres long along which the ions were passed at relatively low velocities and within which the decompositions studied occurred [817, 818, 878]. The trajectories were stabilized by electric radio frequency quadrupole fields. Ionization was by electron impact and decompositions of carbonium ions derived from alkanes were observed over the time range 1/is to 1 ms. 

H. Satake, H. Hasegawa, A. Hirabayashi, Y. Hashimoto, T. Baba, and K. Masuda, Fast multiple electron capture dissociation in a linear radio frequency quadrupole ion trap, Anal. Chem., 79 (2007) 8755-8761. 

D.J. Douglas, J.B. French, Collisional focusing effects in radio frequency quadrupoles, J. Am. Soc. Mass Spectrom., 3 (1992) 398. 

Figure 1. Schematic view of CRYRING. Molecular ions are created in the ion source MINIS, accelerated and mass selected. In some cases they are further accelerated by the Radio Frequency Quadrupole (RFQ), and injected into the ring. The accelerating system is used to further increase the ion energy. Reaction products from the electron cooler section exit the ring and hit detectors located on the 0° arm. The scintillation detector, which detects neutral particles arising from collisions of the stored beam with rest gas molecules, is used as a beam monitor.

The determination of the total ionization cross section of a molecule requires in principle a careful measurement of all quantities in Eq. (2). Partial ionization cross sections can be obtained if the detection of the ion current is restricted to a particular product ion. In the latter case, a mass selective device—e.g., a mass spectrometer—has to be employed. The most commonly used mass spectrometers for this purpose are magnetic, radio-frequency, quadrupole, and time-of-flight mass spectrometers. In all cases, the detection sensitivity of the instrument may vary with the mass of the detected ions and must be known accurately. 

Satake, H., Hasegawa, H., Hirabayashi, A., Hashimoto, Y., Baba, T. (2007) Fast Multiple Electron Capture Dissociation in a Linear Radio Frequency Quadrupole Ion Trap. Anal. Chem. 79 8755-8761. 

The radio frequency quadrupole (RFQ) is used to accelerate protons and heavier ions. It uses four parallel electrodes around the beam axis as shown in O Fig. 50.20. The RFQs operate at high frequencies, typically from tens to hundreds of MHz. The electrodes, which are called vanes, are placed in a cavity forming a resonant structure. The adjacent electrodes have opposite charges. From the end, the RFQ looks like an electric quadrupole. This arrangement of electric field focuses the beam in one plane and defocuses it in the other one. Since the electric field oscillates, a net focusing effect can be obtained along the length of the vanes. 

Piestage, J.D., WiUiams, A., Maleki, L., Djomehri, M.J., and Harabetian, E., Dynamics of charged particles in a Paul radio-frequency quadrupole trap, Phys. Rev. Lett., 66, 2964,1991. 

Collisional focusing effects in radio frequency quadrupoles, J Am Soc Mass Spectrom 3 398-408. 

Figure 14.20 China LEad-AUoy—cooled Reactor (CLEAR) series reactor development plan in the Accelerator-Ehiven Subcritical system project. RFQ, radio frequency quadrupole.

Mass spectrometry using radio-frequency quadrupole fields, N. R. /. Vac. Sci. Tech-nol, 5, 1. 

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