What is MALDI?
The sample for MALDI is uniformly mixed in a large quantity of matrix.
The matrix absorbs the ultraviolet light (nitrogen laser light, wavelength 337 nm) and converts it to heat energy. A small part of the matrix (down to 100 nm from the top outer surface of the Analyte in the diagram) heats rapidly (in several nano seconds) and is vaporized, together with the sample.
What is TOF MS?
Charged ions of various sizes are generated on the sample slide, as shown in the diagram. A potential difference V0 between the sample slide and ground attracts the ions in the direction shown in the diagram. The velocity of the attracted ions v is determined by the law of conservation of energy. As the potential difference V0 is constant with respect to all ions, ions with smaller m/z value (lighter ions) and more highly charged ions move faster through the drift space until they reach the detector. Consequently, the time of ion flight differs according to the mass-to-charge ratio (m/z) value of the ion. The method of mass spectrometry that exploits this phenomenon is called Time of Flight Mass Spectrometry.