Topics - The quadrupole mass spectrometer

The quadrupole mass spectrometer The quadrupole mass spectrometer consists of four precisely straight and parallel rods so arranged that the beam of ions from the ionization source of the spectrometer is directed axially between them. A voltage comprising a DC component and a radio frequency component is applied between adjacent rods, opposite rods being electrically connected. Once inside the quadrupole the ions will oscillate in the (x) (y) direction as a result of the high frequency electric field. The oscillations are only stable for a certain function of frequency and the DC voltage otherwise the ions strike the rods and become dissipated. The mass range of the oscillating ions is scanned by changing the DC voltage and the frequency, keeping the ratio of the DC voltage to the frequency constant. Each mass is detected by an appropriate ion sensor. The resolution of the spectrometer can be increased by either employing eight poles or by connecting two or three qaudupoles in series.