time-of-flight mass spectrometry matrix-assisted laser desorption–ionisation quadrupole time-of-flight mass spectrometry matrix assisted laser desorption ionisation quadrupole time-of-flight mass spectrometry MALDI-QTOF-MS Mass spectrometry where the sample (usually a large organic molecule or biomolecule) is vaporised and ionised using a high-energy pulsed laser. The sample is held in a matrix (such as dihydrobenzoic acid) to protect it from direct laser illumination and to separate the sample molecules. In the first stage the ions are held in a stable orbit by an electric field generated by four parallel electrodes (a quadrupole). In the second stage the sample ions are accelerated to the same (known) kinetic energy and the time taken for each ion to reach a detector at a known distance is measured. This time is dependent on the mass-to-charge ratio of the ion. MALDI-QTOF MS CHMO:0000734 matrix-assisted laser desorption-ionisation quadrupole time-of-flight mass