Definition
Matrix-assisted laser desorption/ionization with time-of-flight detection, a fast mass spectrometry method.
In MALDI, the sample is mixed with a light-absorbing organic matrix, such as α-cyano-4-hydroxycinnamic acid, and dried on a target plate. A pulsed laser vaporises the matrix, which transfers charge to the peptide, producing mainly singly charged ions, [M+H]+. In a time-of-flight analyser, ions are accelerated through a fixed voltage, and their flight time down a tube reveals their mass-to-charge ratio. MALDI-TOF spectra are simple to read because most peptides show one dominant peak. The method is fast, tolerates some salts and suits screening many samples. Koichi Tanaka shared the 2002 Nobel Prize for related soft laser desorption work. ESI is generally preferred when coupling to HPLC.