Quadrupole mass analyzer
From Biocrawler, the free encyclopedia.
Alongside Time of Flight, the quadrupole mass analyzer is one type of mass analyzer used in mass spectrometry. The analyzer is the component of the instrument responsible for guiding sample ions to the detector, based on their mass/charge ratio (m/z).
The Quadrupole consists of four parallel metal rods. A radio frequency voltage is applied across one pair of rods, and a direct current voltage across the other. Ions travel down the quadrupole in between the rods. Only ions of a certain m/z will reach the detector for a given ratio of voltages: other ions have unstable oscillations and will collide with the rods. This allows selection of a particular ion, or scanning by varying the voltages.
A series of three quadrupoles can be used, this is known as Triple Quadrupole mass spectrometry. The first and third quadrupoles are mass filters, and the middle one is a collision centre. This allows the study of fragments, useful in structural studies.
External links
- Quadrupole mass spectrometry (http://www.chem.vt.edu/chem-ed/ms/quadrupo.html) Page from the Chemistry Hypermedia Project, summary of the technique and useful diagram
