What is the purpose of multiple reaction monitoring (MRM) in LC-MS/MS?

What is the purpose of multiple reaction monitoring (MRM) in LC-MS/MS?

• A. To monitor specific precursor-to-product ion transitions for each analyte, increasing selectivity and enabling accurate quantification.
• B. To calibrate instrument's temperature.
• C. To run a single ion detection.
• D. To identify the chemical structure via NMR.

Answer: (A)

In LC-MS/MS, multiple reaction monitoring targets a known molecular signature for each analyte by tracking a specific precursor ion and its chosen product ion. This targeted transition provides high selectivity because only ions that produce that exact fragmentation pattern will be detected, which suppresses interference from other molecules in complex samples. In a triple quadrupole instrument, the first quadrupole isolates the precursor, the middle acts as a collision cell to generate fragments, and the third quadrupole selects the specific product; monitoring only that transition yields clean signals and improves quantification accuracy, even at low concentrations. You can monitor many analytes in one run by assigning different transitions to each, enabling multiplexed quantitative assays. This approach is the reason MRM is preferred for targeted quantitative LC-MS/MS analyses. It’s not used for basic temperature calibration, single ion detection without fragmentation, or structure elucidation by NMR.