QTOFs

QTOF stands for Quadrupole Time-of-Flight mass spectrometer, a hybrid instrument that combines a quadrupole mass filter with a time-of-flight analyzer to measure the mass-to-charge ratio of ions with high speed and accuracy. Ions are typically generated by electrospray ionization (ESI) or matrix-assisted laser desorption/ionization (MALDI) and enter the instrument through the source. A quadrupole can act as a precursor selector for MS/MS experiments or function in full-scan mode. After selection, ions are accelerated into the time-of-flight region, where their flight times are recorded and converted to m/z values. Many QTOFs include a collision cell for controlled fragmentation and a reflectron to enhance resolution and mass accuracy.

Operation and performance characteristics vary by model but share common strengths. The combination of a quadrupole with a TOF analyzer provides rapid data acquisition and the ability to obtain high-resolution, accurate-mass measurements. Mass accuracy is typically very high with proper calibration and reference standards, and the resolving power is sufficient to distinguish closely spaced peaks in complex mixtures. The design supports a wide mass range and high sensitivity, making it suitable for detecting low-abundance ions in complex samples. Data can be acquired in various modes, including full-scan MS and tandem MS (MS/MS), enabling both profiling and structural characterization.

Applications and data strategies. QTOFs are widely used in proteomics, metabolomics, and small-molecule analysis, as well as pharmaceutical and clinical research. They support data-dependent acquisition, where selected ions trigger MS/MS, and data-independent acquisition approaches, such as SWATH-MS, which provide comprehensive fragmentation data for large-scale analyses. Data processing typically includes calibration with lock masses, peak detection, deconvolution, and, when appropriate, formula prediction and database searching.