Does decarboxylation make 2,5-dihydroxybenzoic acid special in matrix-assisted laser desorption/ionization?
BACKGROUND
Among the six positional isomers of dihydroxybenzoic acid (DHB), 2,5-DHB is a more favorable matrix for use in matrix-assisted laser desorption/ionization (MALDI) than the other isomers because of its high ion-generation efficiency at 337 and 355 nm. The generation of hydroquinone or p-benzoquinone through the decarboxylation of 2,5-DHB has been suggested to play a crucial role in the ion-generation efficiency of 2,5-DHB.


METHODS
The mass spectra of desorbed neutrals generated from MALDI were measured using electron impact ionization (70 eV) and a quadrupole mass spectrometer and vacuum ultraviolet (118 nm) photoionization and a time-of-flight mass spectrometer. The mass spectra of desorbed ions generated from MALDI were investigated using a time-of-flight mass spectrometer. The dissociation barrier height and dissociation rate of decarboxylation were calculated by an ab initio method and RRKM theory.


RESULTS
Decarboxylation of neutral 2,5-DHB and 2,5-DHB cations was not observed. Theoretical calculations indicated that decarboxylation of neutral 2,5-DHB and 2,5-DHB cations is too slow to occur.


CONCLUSIONS
The high ion-generation efficiency of the 2,5-DHB matrix at 337 and 355 nm is not related to decarboxylation.
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.
Hsu Chen
HC
Hsu
I-Chung
IC
Lu
Pei-Hsuan
PH
Lin
Yuri A
YA
Dyakov
Arnab
A
Bagchi
Chih-Yuan
CY
Lin
Sheng-Wei
SW
Hung
Yuan-Tseh
YT
Lee
Chi-Kung
CK
Ni
D002412:Cations / Q000737:chemistry; D003653:Decarboxylation; D005841:Gentisates / Q000737:chemistry*; D006873:Hydroquinones / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
D002412:Cations; D005841:Gentisates; D006873:Hydroquinones; C010925:2,5-dihydroxybenzoic acid; C031927:hydroquinone