A triple quadrupole mass spectrometer is a tandem mass spectrometer

Tandem mass spectrometry

Tandem mass spectrometry, also known as MS/MS or MS2, involves multiple steps of mass spectrometry selection, with some form of fragmentation occurring in between the stages.-Tandem MS instruments:...

 consisting of two quadrupole mass spectrometers in series, with a (non mass-resolving) radio frequency (RF) only quadrupole between them to act as a collision cell for collision-induced dissociation

Collision-induced dissociation

In Mass spectrometry, Collision-induced dissociation , referred to by some as collisionally activated dissociation , is a mechanism by which to fragment molecular ions in the gas phase. The molecular ions are usually accelerated by some electrical potential to high kinetic energy and then allowed...

. The first (Q₁) and third (Q₃) quadrupoles serve as mass filters, whereas the middle (q₂) quadrupole serves as a collision cell. This collision cell is an RF only quadrupole (non-mass filtering) using an inert gas such as Ar, He, or N₂ gas to provide collision-induced dissociation

Collision-induced dissociation

In Mass spectrometry, Collision-induced dissociation , referred to by some as collisionally activated dissociation , is a mechanism by which to fragment molecular ions in the gas phase. The molecular ions are usually accelerated by some electrical potential to high kinetic energy and then allowed...

 of a selected precursor ion that is selected in Q₁. Subsequent fragments are passed through to Q₃ where they may be filtered or scanned. This configuration is often abbreviated QqQ, here Q₁q₂Q₃.

Structural mass spectrometry

This alignment of two mass spectrometers in succession with a collision quadrupole in between allows to elucidate the structure of the ionised sample molecules. Four main modes can be performed as follows.

Product ion scan

• The first quadrupole Q₁ is set to select an ion of a known mass, which is fragmented in q₂. The third quadrupole Q₃ is then set to scan the entire m/z range, giving information on the sizes of the fragments made. From the ion fragmentation information, the structure of the original ion can be deduced. This experiment is commonly performed to identify transitions used for quantification by tandem MS.

Precursor ion scan

• A certain product ion is selected in Q₃, and the precursor masses are scanned in Q₁. This experiment is selective for ions having a particular functional group (e.g., a phenyl group) released by the fragmentation in q₂.

Neutral loss scan

• Both Q₁ and Q₃ are scanned together, but with a constant mass offset. This allows the selective recognition of all ions which, by fragmentation in q₂, lead to the loss of a given neutral fragment (e.g., H₂O, NH₃). Similar to the precursor ion scan, this technique is also useful in the selective identification of closely related class of compounds in a mixture.

Selected reaction monitoring (SRM) / Multiple reaction monitoring (MRM)

• Both Q₁ and Q₃ are set to a selected mass, allowing only a distinct fragment ion from a certain precursor ion to be detected. SRM is a very selective analysis mode, which can increase sensitivity. If Q₁ and/or Q₃ is set to more than a single mass, this configuration is called multiple reaction monitoring.

History

The arrangement of three quadrupoles was first developed by Morrison of LaTrobe University, Australia for the purpose of studying the photodissociation of gas-phase ions. The first triple-quadrupole mass spectrometer was developed at Michigan State University

Michigan State University

Michigan State University is a public research university in East Lansing, Michigan, USA. Founded in 1855, it was the pioneer land-grant institution and served as a model for future land-grant colleges in the United States under the 1862 Morrill Act.MSU pioneered the studies of packaging,...

by Enke and Yost in the late 1970s.