quadrupol mass analyzers
QMS, QTOF, TQMS
Quadrupole mass analyzers can be used as an upstream mass filter in TOF mass spectrometry (QTOF). With their help, all ions can be eliminated for the detection of certain substances that are not within the desired range from mass to charge. A quadrupole mass analyzer consists of the arrangement of two oppositely identical electrical or magnetic dipoles with a fixed distance over their entire length. In mass filter analysis with an electric quadrupole, the inertia of the introduced particles is used for selection: the light particles are destabilized in one of the levels and the heavy particles in the other level by means of an applied alternating voltage. Quadrupoles can also be used to focus the ion beam in a mass spectrometer, e.g. to align the ions with a collision cell and to record the fragments produced there by means of time-of-flight measurement.
Note: There are also mass spectrometers that use quadrupoles and similar arrangements to record an entire mass spectrum (QMS). In terms of their detection capabilities, these do not come close to the performance of the TOF-MS, because in these devices the stability range is scanned over the entire m / Q range and a new measurement is carried out at every step. As a result, such measurements require a significantly higher investment of time. Triple quadrupole mass spectrometers (TQMS) should also be mentioned at this point. These are tandem mass spectrometers, which consist of two quadrupole mass analyzers connected in series and are separated by a (non-mass-resolving) high-frequency quadrupole, which serves as a cell for the collision-induced dissociation. The aim is to increase the sensitivity of the measurement. However, this coupling does not achieve the performance of a TOF measurement either.