Detection of Neutral Species in the MALDI Plume Using Femtosecond Laser Ionization: Quantitative Analysis of MALDI-MS Signals Based on a Semi-equilibrium Proton Transfer Model
Detection of Neutral Species in the MALDI Plume Using Femtosecond Laser Ionization: Quantitative Analysis of MALDI-MS Signals Based on a Semi-equilibrium Proton Transfer Model
复制标题
使用飞秒激光电离检测 MALDI 羽流中的中性物质：基于半平衡质子传递模型的 MALDI-MS 信号定量分析
DOI：
10.1021/acs.jpca.6b09591
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发表时间：
2017
影响因子：
2.9
通讯作者：
Kennosuke Hoshina
中科院分区：
文献类型：
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作者：
Tatsuro Shirota;Masashi Tsuge;Yasumasa Hikosaka;Koichi Soejima;Kennosuke Hoshina
我们使用飞秒激光电离光谱法研究了基质辅助激光解吸和电离 (MALDI) 羽流中的中性物质，同时测量了由脉冲紫外激光照射引起的相同 MALDI 事件的标准 MALDI 光谱。羽流中中性物质的比率 [A]p/[M]p（A = 苯丙氨酸 (Phe) 或丙氨酸 (Ala)，M = 2,5-二羟基苯甲酸 (DHB)）被证实与 [A]0/[M]0= 4 × 10–4–1 范围内的样品混合物中性物质的比率相同，表明广泛采用的近似值 [A]p/[M]p= 的有效性质子转移反应的反应商中的[A]0/[M]0 MH++ A ⇄ M + AH+。首次在热质子传递模型中引入了代表热平衡程度的有效参数。基于该半平衡模型的数值模拟成功地再现了 MALDI 信号强度 AH+ 和 MH+ 的变化，其中两个参数为：Phe/DHB 和 Ala/DHB 系统的电离基质分数 a≤ 10–5 和有效温度 T= 1200 和 1100 K。这些值与之前通过不同实验方法确定的值非常吻合。 Phe/DHB 和 Ala/DHB 体系的热平衡程度分别为 95% 和 98%，表明质子转移反应几乎达到热平衡。
We investigated neutral species in the matrix-assisted laser desorption and ionization (MALDI) plume using femtosecond laser ionization spectrometry with simultaneous measurement of the standard MALDI spectrum of the identical MALDI event induced by pulsed UV laser irradiation. The ratio of neutral species in the plume [A]p/[M]p(A = phenylalanine (Phe) or alanine (Ala), M = 2,5-dihydroxybenzoic acid (DHB)) was confirmed to be the same as that of the sample mixture in the range of [A]0/[M]0= 4 × 10–4–1, indicating the validity of the widely adopted approximation [A]p/[M]p= [A]0/[M]0in the reaction quotient of the proton transfer reaction MH++ A ⇄ M + AH+. An effective parameter representing the extent of thermal equilibrium in the thermal proton transfer model is introduced for the first time. Numerical simulation based on this semiequilibrium model successfully reproduced variations of MALDI signal intensities AH+and MH+with two parameters: the fraction of ionized matrixa≤ 10–5and an effective temperatureT= 1200 and 1100 K for Phe/DHB and Ala/DHB systems, respectively. These values show good agreement with those determined previously by different experimental approaches. The extent of thermal equilibrium was determined to be 95% and 98% for Phe/DHB and Ala/DHB systems, respectively, suggesting that the proton transfer reactions almost proceed to their thermal equilibrium.