Quadrupole Mass Spectrometer (MS) / Quadrupole Mass Analyzer

Quadrupole mass spectrometers are perhaps the simplest of mass spec instruments. Functioning effectively like a radio, the quadrupole MS – so-named because of its four charged rods, which run parallel to the flight paths of the ions it measures – filter ions by mass-to-charge ratio (m/z) by altering the voltages in the rods. Quadrupole mass spectrometers are available in a variety of formats, including a single quadrupole mass spectrometer, a triple quadrupole MS (three quadrupoles arranged in tandem), and a Q-TOF (a triple quad variant in which the third quadrupole is replaced with a time-of-flight mass analyzer).

Quadrupole mass analyzers are often used for targeted, quantitative applications and can be used either to measure one or a few given ions in a mixture, or to scan across a range of m/z values. Depending on the configuration, they can facilitate both MS and MS/MS applications. For instance, in a triple-quadrupole mass spectrometer, you can select ions for analysis in the first quadrupole, fragment them by collision with a gas in the second quadrupole, and analyze the resulting fragmentation ions in the third quadrupole.