Multiple Reaction Monitoring (MRM)
Definition
An LC-MS/MS acquisition mode in which the first quadrupole (Q1) selects a precursor ion at a specific m/z, the second (Q2) fragments it with a collision gas, and the third (Q3) monitors one or more specific product ions. MRM is highly specific because both the precursor mass and the fragmentation product are required to match simultaneously.
- Instrument type
- LC-MS/MS (liquid chromatography with triple quadrupole mass spectrometer)
- Identification criterion
- Two MRM transitions per analyte plus retention time match
- Key advantage
- Dual mass matching (precursor and products) makes compound identification highly specific
Common questions
What is MRM and why is it used in forensic analysis?+
MRM stands for Multiple Reaction Monitoring, an LC-MS/MS mode that tracks specific precursor ions and their fragmentation products. Forensic labs use it because monitoring both the parent mass AND the fragment masses simultaneously makes compound identification highly specific and reliable.
What makes MRM different from other mass spec methods?+
MRM requires a match on two levels: the precursor ion selected in the first quadrupole and the product ions detected in the third quadrupole. This dual-mass requirement means fewer false positives than methods that look at only one mass at a time.
How does a lab confirm an explosive or drug compound using MRM?+
The standard practice is to measure two MRM transitions per compound and match the retention time. When both transitions hit and the timing is correct, the forensic scientist can confidently report a positive identification.
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Explained in these topics
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