title: Reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry.
abstract: The mechanisms of the reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry (MALDI) are studied. In MALDI mass spectra, ions cationized by copper mostly contain Cu(I) even if Cu(II) salts are added to the sample. It was found that Cu(II) was reduced to Cu(I) by gas-phase charge exchange with matrix molecules, which is a thermodynamically favorable process. Under some conditions, large amounts of free electrons are present in the plume. Cu(II) can be even more efficiently reduced to Cu(I) by free electron capture in the gas phase. The matrices studied in this work are nicotinic acid, dithranol, and 2,5-dihydroxybenzoic acid.
authors.affiliation: Department of Chemistry, Swiss Federal Institute of Technology (ETH), ETH-Hönggerberg, Zurich, Switzerland.
authors.forename: Juan
authors.initials: J
authors.lastname: Zhang
authors.forename: Vladimir
authors.initials: V
authors.lastname: Frankevich
authors.forename: Richard
authors.initials: R
authors.lastname: Knochenmuss
authors.forename: Sebastian D
authors.initials: SD
authors.lastname: Friess
authors.forename: Renato
authors.initials: R
authors.lastname: Zenobi