triplequadrupole

A triple quadrupole mass spectrometer is a type of tandem mass spectrometry instrument that uses three quadrupole mass analyzers in series, typically labeled Q1, Q2, and Q3. In operation, Q1 selects a specific precursor ion by its mass-to-charge ratio, Q2 serves as a collision cell where the selected precursor undergoes collision-induced dissociation to form product (fragment) ions, and Q3 analyzes the resulting product ions by m/z. This arrangement provides a highly selective and sensitive platform for targeted analyses.

The dominant operating mode is multiple reaction monitoring (MRM), sometimes called selected reaction monitoring (SRM). In MRM, a predefined set of precursor-to-product ion transitions is continuously monitored, yielding strong signal from the target analyte with reduced background from matrix interferences. The method offers high sensitivity, wide dynamic range, and robust quantitation even in complex samples. Internal standards, often isotopically labeled analogs, are commonly used to improve accuracy and precision.

Other modes are available, including product ion scans, precursor ion scans, and neutral loss scans, but these are less common for routine quantification and more typical of method development or structural elucidation. Triple quadrupoles are widely applied in clinical pharmacology, bioanalysis, environmental and food safety testing, and targeted proteomics, where rapid, multiplexed, low-level measurements are required.

Advantages include high selectivity and sensitivity, fast duty cycles, and compatibility with various ionization methods such as electrospray and atmospheric pressure chemical ionization. Limitations involve reliance on predefined transitions, which constrains discovery workflows, along with method development, validation demands, and higher instrument and maintenance costs compared with single-quadrupole systems.