Practice question

Matrix-assisted laser desorption ionization mixes analyte with an excess of organic matrix such as alpha-cyano-4-hydroxycinnamic acid that strongly absorbs ultraviolet laser light. A pulsed nitrogen laser at 337 nm irradiates the dried co-crystal, causing matrix excitation, rapid sublimation, and proton transfer to analyte molecules without extensive fragmentation. Electrospray ionization uses high-voltage liquid spray, electron ionization uses energetic electron beam, and fast atom bombardment uses atom beam. Only MALDI relies on photo-absorbing matrix together with laser desorption for gentle vaporization and ionization of large proteins and peptides.