title: Role of three-body recombination for charge reduction in MALDI process.
abstract: Ions in Matrix-Assisted Laser Desorption/Ionization (MALDI) are predominantly singly charged for small analyte molecules. With the estimated high number density and low temperature of electrons, the three-body recombination mechanism is attractive and should be considered as an important cause for the charge reduction in the plume. Theoretical calculations indicate that the rate coefficient of the three-body recombination is about 50 times higher than that of the two-body recombination if the analyte molecule has insufficient degrees of freedom. Experimental results show that, for small analyte molecules, the ratio of AH2(2+)/AH(+) is close to the theoretical 5% value from the three-body recombination modeling and this ratio declines with the increasing electron and matrix molecule number density caused by greater laser irradiance. The ratio of [A + 2](+)/[A + 1](+) is higher than the theoretical isotopic value, and the excess [A + 2](+) could exclusively result from the three-body recombination collisions. Further evidence demonstrates that [A + 2](+)/[A + 1](+) increases with electron number density, which is in correspondence with the model. All of these theoretical and experimental results indicate that three-body recombination is an essential charge reduction mechanism for small molecules in the MALDI plume.
authors.affiliation: Department of Chemistry and The Key Laboratory of Analytical Sciences, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Yiming
authors.initials: Y
authors.lastname: Lin
authors.forename: Zhibin
authors.initials: Z
authors.lastname: Yin
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Wang
authors.forename: Weifeng
authors.initials: W
authors.lastname: Li
authors.forename: Wei
authors.initials: W
authors.lastname: Hang
mesh_terms: D001414:Bacitracin / Q000032:analysis*; D003373:Coumaric Acids / Q000737:chemistry*; D005841:Gentisates / Q000737:chemistry*; D007834:Lasers; D009113:Muramidase / Q000032:analysis* / Q000378:metabolism; D015688:Oncogene Protein pp60(v-src) / Q000032:analysis*; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000032:analysis*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D003373:Coumaric Acids; D005841:Gentisates; D010446:Peptide Fragments; C098708:peptide A; D001414:Bacitracin; C007175:alpha-cyano-4-hydroxycinnamate; C026461:bacitracin A; D015688:Oncogene Protein pp60(v-src); D009113:Muramidase; C010925:2,5-dihydroxybenzoic acid