Quantifier and Qualifier Transitions
Definition
The most intense MRM transition is the quantifier and is used for the concentration calculation. The second (and sometimes third) transition is the qualifier and confirms identity. The ratio of quantifier to qualifier intensity in the sample must match the same ratio in a reference standard within plus or minus 20 to 30 percent.
- Quantifier role
- Most intense MRM transition, used for concentration
- Qualifier role
- Confirms analyte identity
- Acceptance window
- Plus or minus 20 to 30 percent ratio match
- Technique
- Tandem mass spectrometry, MRM mode
Common questions
Why is a single MRM transition not sufficient to confirm an analyte's identity?+
One transition alone can be matched by an interfering compound with the same precursor-to-product mass transition, so a second qualifier transition with a known intensity ratio to the quantifier is required to confirm the peak truly represents the target analyte and not a coincidental interference.
What does it mean when the qualifier-to-quantifier ratio falls outside the accepted tolerance?+
A ratio outside the plus-or-minus 20 to 30 percent window signals a likely interference or matrix effect distorting one of the transitions, and the result is typically flagged as not confirmed rather than reported as a positive identification.
Related terms
- 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...
- 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....
- 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...
- Tandem MS (MS/MS)
- Two stages of mass selection in series with a fragmentation step in between. The first stage selects a precursor ion, a collision...