Description of MALDI ToF Mass Spectrometry

Sample: Supernatant of tryptic digest of a gel spot are mixed with the "matrix" and applied on the target and dried. Microcrystalline layer of Energy transfer molecules = Light absorbing matrix: Sinapinic acid, Dihydroxybenzoic acid, etc.

Matrix assisted laser desorption ionization (MALDI): The light energy of the pulsed laser is absorbed by the small matrix molecules. They move away from the target with supersonic speed. The small molecules take the larger ones (peptides) with them. While this happens, the charged matrix molecules transfer their charges on the peptide molecules. With an accelerator grid with high voltage the ions are moved into the high vacuum ToF tube.

Pulsed extraction: All ions with different masses are accelerated to the same kinetic energy by switching the high voltage grid on with a time delay after ionization.

Time of Flight separation (ToF): The light ions arrive at the detector sooner than the heavy ions.

Mass determination: Velocities of molecules are reversely proportional to the square roots of their masses.

Detection: Secondary electron multiplier

10 - 50 spectra from a single laser shot are summed for signal averaging to achieve accurate mass determination.