Tandem MS (MS/MS)
Definition
Two stages of mass selection in series with a fragmentation step in between. The first stage selects a precursor ion, a collision cell fragments it, and the second stage analyses the product ions. Selectivity is the product of two mass filters and a known fragmentation pathway.
- Configuration
- Two mass analyzers separated by a collision cell for fragmentation
- Selectivity basis
- Product of two mass filters plus known fragmentation pathway
Common questions
What is the main difference between single mass spectrometry and tandem MS?+
Tandem MS uses two stages of mass selection with a fragmentation step in between. The first stage picks a precursor ion, a collision cell breaks it apart, and the second stage analyzes the fragments. This two-step process gives you much higher selectivity because you're filtering on both the intact molecule and its known breakdown products.
What are the key steps that happen inside a tandem MS instrument?+
First, a precursor ion is selected and sent to a collision cell. There, the ion breaks apart into smaller product ions. Then the second mass analyzer scans and detects these fragments. Different instrument types like triple quadrupole, Q-TOF, and ion-trap systems do this in different ways.
Why is tandem MS useful for forensic analysis?+
Tandem MS targets specific molecules by looking at both their mass and their fragmentation pattern. This means you can pick out drugs, poisons, or trace chemicals even when the sample is messy or contains many similar compounds. The combination of two mass filters and a known fragmentation pathway makes it very selective and reliable.
Related terms
- Accurate Mass
- A mass measured to four or more decimal places, sufficient to compute a unique molecular formula. High-resolution accurate-mass (HRAM) instruments (Q-TOF, Orbitrap,...
- Accurate Mass and Mass Defect
- On a Q-TOF or Orbitrap, the measured m/z is reported to four decimal places at parts-per-million accuracy. The deviation from the nominal...
- Base Peak
- The most intense peak in a mass spectrum, normalised to 100 percent relative abundance. All other peaks in the spectrum are reported...
- CID and HCD
- Collision-induced dissociation. The precursor is accelerated and collides with a neutral gas (nitrogen, argon, helium) in the collision cell. Internal energy converts...
- Deuterated Internal Standard
- An isotopologue of the analyte where two to five hydrogens are replaced by deuterium. Same chromatographic and ionisation behaviour, slightly higher mass....
- Mass-to-Charge Ratio (M/z)
- The fundamental MS measurement: the mass of an ion divided by its charge number. A singly charged ion of mass 250 Da...
- Molecular Ion (M+)
- The intact ionised molecule with no fragmentation, formed by removing a single electron from the parent. Its m/z gives the molecular weight...
- MRM (Multiple Reaction Monitoring)
- A targeted MS/MS scan mode on a triple quadrupole that monitors specific precursor-to-product ion transitions, with two transitions per analyte (quantifier and...
- Quantifier and Qualifier Transitions
- The most intense MRM transition is the quantifier and is used for the concentration calculation. The second (and sometimes third) transition is...
- Resolution
- The ability of a mass analyser to distinguish two ions of nearly equal m/z, defined as m/Δm at a given peak. A...
Explained in these topics
- Mass Spectrometry: Principles, Ionisation and Mass AnalysersTwo stages of mass selection separated by a fragmentation step. The first analyser picks the precursor ion, a collision cell breaks it apart, and the second an...
- Tandem Mass Spectrometry (MS/MS) and Spectral InterpretationTwo stages of mass selection in series with a fragmentation step in between. The first stage selects a precursor ion, a collision cell fragments it, and the se...