ABSTRACT
Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is one of the most widely used soft ionization methods for biomolecules. Atmospheric pressure-MALDI was introduced, increasing the ease of sample preparation and allowing for the analysis of volatile molecules, as the sample no longer needs to be placed under vacuum prior to analysis. In MALDI, analytes are incorporated into organic matrices in a solid or viscous phase. MALDI is based on the use of a matrix that absorbs the energy of the laser irradiation and is, thus, crucial for the successful generation of ions. Different mechanisms have been proposed to explain MALDI ionization. All are in agreement with the presence of two different steps: primary ion formation from the matrix and secondary ion formation of the analyte originating from the gas phase interaction of reactive matrix ions and neutral molecules of the analyte. Several theories have been developed to explain the desorption of large molecules by MALDI.
