Sample preparation for MALDI mass analysis of peptides and proteins

Sample preparation may be the most crucial step in mass spectrometric analysis of peptides and proteins by MALDI. The free dipolar ionic peptides or proteins must be incorporated into a crystalline solid solution that is comprised of excess solvent (the matrix), which modulates desorption/ionization by preferentially absorbing the laser energy at the irradiation wavelength and laser pulse intensity being employed. Usually the cocrystalline sample and matrix are prepared by mixing solutions of each component and permitting the mixture to crystallize through evaporation of the solvents. Two methods employing this approach are presented in this unit: the dried drop method and the rapid evaporation method.