What is the primary function of the quadrupole in a quadrupole mass spectrometer?

The primary function of the quadrupole in a quadrupole mass spectrometer is to separate ions based on their mass-to-charge ratio (m/z). The quadrupole acts as a mass filter, allowing only ions with a specific mass-to-charge ratio to pass through while filtering out other ions. This separation is achieved by applying radiofrequency and direct current voltages to the quadrupole rods in a precise manner, creating a stable and selective field that allows ions of a particular mass-to-charge ratio to traverse the quadrupole and reach the detector.