Matrix-assisted laser desorption ionization spectrometry or MALDI is an ionization technique employed to acquire accurate molecular mass data for polar biopolymers with molecular masses ranging from a few to a hundred thousand Daltons.

The sample preparation process involves mixing an analyte solution with a matrix material, such as 2,5-dihydroxybenzoic acid. This mixture is then deposited on a probe inserted into the mass spectrometer.

When the ultraviolet or infrared laser beam is focused on the surface, the matrix absorbs the laser energy, leading to desorption and ionization of sample molecules through a proton transfer from the matrix to the analyte molecule, generating protonated ions.

The newly formed ions are accelerated by an electric field and separated based on their mass-to-charge ratio in a time-of-flight mass analyzer.

The resulting mass spectrum can be analyzed to determine the molecular mass of the biomolecule under investigation.