Describe how MALDI works.

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MALDI works by softly desorbing and ionizing large molecules with a laser in the presence of a matrix. The matrix absorbs the laser light and transfers the energy to the analyte, enabling rapid desorption into the gas phase while imparting a charge. This gentle, laser-assisted process often yields intact molecular ions (such as [M+H]+ or other adducts) with minimal fragmentation, which is essential for analyzing big biomolecules like proteins and peptides. This contrasts with harder ionization methods, such as electron impact, which ionize molecules directly in the gas phase and typically cause extensive fragmentation. Other ionization approaches, like field ionization or methods implied by “nuclear resonance ionization,” operate on different principles and are not used in MALDI. The key feature is soft ionization by a laser-induced desorption from a matrix, producing usable ions for mass spectrometric detection.