Hsu Hsu Chen, Lu I-Chung, Lin Pei-Hsuan, Dyakov Yuri A, Bagchi Arnab, Lin Chih-Yuan, Hung Sheng-Wei, Lee Yuan-Tseh, Ni Chi-Kung
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.
Rapid Commun Mass Spectrom. 2014 May 30;28(10):1082-8. doi: 10.1002/rcm.6885.
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.
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.
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.
The high ion-generation efficiency of the 2,5-DHB matrix at 337 and 355 nm is not related to decarboxylation.
在二羟基苯甲酸（DHB）的六种位置异构体中，2,5 - DHB比其他异构体更适合用作基质辅助激光解吸/电离（MALDI）的基质，因为它在337和355纳米处具有高离子产生效率。有人提出，通过2,5 - DHB的脱羧作用生成对苯二酚或对苯醌在2,5 - DHB的离子产生效率中起关键作用。
使用电子轰击电离（70电子伏特）和四极杆质谱仪以及真空紫外（118纳米）光电离和飞行时间质谱仪测量由MALDI产生的解吸中性物质的质谱。使用飞行时间质谱仪研究由MALDI产生的解吸离子的质谱。通过从头算方法和RRKM理论计算脱羧的解离势垒高度和解离速率。
未观察到中性2,5 - DHB和2,5 - DHB阳离子的脱羧。理论计算表明，中性2,5 - DHB和2,5 - DHB阳离子的脱羧太慢而无法发生。
2,5 - DHB基质在337和355纳米处的高离子产生效率与脱羧无关。
