The quadrupole mass analyzer rods are charged with a variable ratio of RF and DC voltages. This applied amplitude of voltages generates an electric field that gives stable oscillations to ions with a specific m/z and gives unstable oscillations to all others.
When the MS applies one particular set of RF and DC voltages to the quadrupole rods, only ions of a single m/z value (for example, m/z 180) are maintained within bounded oscillations as their velocity carries them through the mass analyzer.
At the same time, all other ions undergo unbounded oscillations. These ions strike one of the rod surfaces, become neutralized, and are either pumped away or ejected from the rod assembly.
Later, both RF and DC voltages change, and ions of a different m/z (for example, m/z 181) are allowed to pass, while all other ions (including m/z 180) become unstable and undergo unbounded oscillations. This process of transmitting ions by one m/z value after another continues as the RF and DC voltages change in value.
The more closely the electric field generated by a set of quadrupole rods approximates a hyperbolic geometry, the better the rods’ operating characteristics are. As a result, the precision hyperbolic surface of the quadrupole rods provide excellent sensitivity, peak shape, and resolution, as well as high mass transmission.