Quadrupole with Pre-Filter

Exhibit no. 666

The quadrupole mass analyzer separates ions based on the stability of their trajectories in the oscillating electric fields. It consists of four parallel rods with a hyperbolic or circular cross-section. Typical rod diameters are between 5 and 12 mm with rod lengths between 100 and 200 mm. The opposing quadrupole rods are connected together electrically, and a radio frequency (RF) voltage and a DC voltage is applied between one pair of rods and the other. Quadrupole mass analyzers are usually operated at a fixed frequency typically between 1 and 10 MHz.  Within the region between the rods, the quadrupole electric field affects the motion of the ions in the XY plane, while the ion motion along the Z-axis is not affected. The quadrupole mass analyzer acts as a mass filter. Only ions of a certain mass-to-charge ratio will reach the detector for a given ratio of RF and DC voltages: other ions have unstable trajectories and will collide with the rods. This permits the selection of an ion with a particular m/z or scanning for a range of m/z-values by continuously varying the applied voltage. The quadrupole mass analyzer was developed in parallel with the quadrupole ion trap by the Nobel prize-winning mass spectrometry pioneer, Wolfgang Paul.