Quadrupole mass analyzer with cylindrical rods

Figure 11.19 Schematic diagram of a quadrupole mass analyzer. Four cylindrical or parabolic metal rods are held in a parallel configuration with fixed or oscillating electric fields applied, as negative or positive, to opposing pairs of rods. The frequency and field strength can be so adjusted that only one ion of a given m/z can make the journey down the axis between the rods to the detector. The electric fields can be gradually adjusted or scanned (over a matter of mseconds) to allow a series of ions to reach the detector, thus giving the mass spectrum.

Figure 2.15. Schematic of a quadrupole analyzer, (a) A hyperbolic cross-section (b) cross-section of cylindrical rods (c) the operating principle of a quadrupole mass filter. The x-direction pair of rods acts like a high pass filter so ion C (with low m/z) is not allowed through, and the y-direction pair of rods acts like a low pass filter and takes care of ion A (with high m/z). Only ion B having an m/z in the stable range is allowed through the quadrupole mass filter for subsequent detection. Reprinted from A. Westman-Brinkmalm and G. Brinkmalm (2002). In Mass Spectrometry and Hyphenated Techniques in Neuropeptide Research, J. Silberring and R. Ekman (eds.) New York John Wiley Sons, 47-105. With permission of John Wiley Sons, Inc.

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