How Does a Mass Spectrometer Identify Molecules?

Mass spectrometry involves three steps: ionisation, separation, and detection. First, sample molecules are ionised — given an electrical charge — using methods like electron impact, electrospray, or MALDI (matrix-assisted laser desorption). The ions are then accelerated into a mass analyser (quadrupole, time-of-flight, or magnetic sector) that separates them based on their mass-to-charge ratio (m/z). Finally, a detector records the abundance of ions at each m/z value, producing a mass spectrum — a unique chemical "fingerprint." Modern tandem mass spectrometers (MS/MS) fragment ions further for structural identification, achieving sensitivities in the parts-per-trillion range.