Figure 1.

Principle of matrix-assisted laser desorption/ionization (MALDI-TOF MS) time-of-flight mass spectrometry. (A) Analyte molecules are first mixed with matrix molecules in a ratio of about 1 to 5,000. Upon solvent evaporation, matrix-analyte co-crystals form. In the ion source of the instrument, irradiation of these with a brief laser pulse initiates the desorption-ionization events. (B) The newly formed molecular ions are accelerated in the source of the instrument by a constant potential difference, giving all of the ions of the same charge the same energy. Ions are therefore separated in time according to their mass as they travel the length of the time-of-flight. (C) MALDI-TOF mass spectrum obtained in the positive ionization mode from a complex protein mixture. By a large majority, essentially singly charged ions (z = 1) are observed. Reprinted by permission from Reference 131.