Quadrupole Mass Spectrometers

A quadrupole mass spectrometer contains four parallel cylindrical rods which can scan or filter sample ions based on their mass-to-charge ratio. Opposing rods are connected electrically and a radio frequency voltage is applied between the pairs of rods. Ions travel between the rods and only ions with a specific mass-to-charge ratio will exit the quadrupole; other ions will collide with the rods. The desired mass-to-charge ratio can be altered by changing the applied voltage. Triple quadrupole mass spectrometry makes use of the same technology, but uses a linear series of three quadrupoles to improve sensitivity and selectivity. This type of spectrometry is useful when studying particular ions of interest since it is able to stay tuned to a single ion for extended periods of time.