Ghost peaks observed after atmospheric pressure matrix-assisted laser desorption/ionization experiments may disclose new ionization mechanism of matrix-assisted hypersonic velocity impact ionization.
Ghost peaks observed after atmospheric pressure matrix-assisted laser desorption/ionization experiments may disclose new ionization mechanism of matrix-assisted hypersonic velocity impact ionization.
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DOI：
10.1002/rcm.7248
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发表时间：
2015-08-30
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影响因子：
--
通讯作者：
Moskovets E
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作者：
Moskovets E
了解MALDI的机制有望提高质谱领域许多已建立应用的灵敏度和特异性。本文报道了一个偶然的观察后电离实验中进行的样品已从标准大气压（AP）-MALDI源的显着离子产率。这后电离被解释为微粒以高超音速移动到固体表面的碰撞。计算表明，在这种碰撞过程中释放的热能接近于传统MALDI中的顶部基质层吸收的热能。包含基质和分析物的微粒可以在样品烧蚀期间从入口毛细管内产生的膜上分离，并通过流过毛细管的流动加速。这些观测为激光和无激光基质辅助电离中离子的形成提供了新的视角。一个AP-MALDI离子源与三级高压离子漏斗系统联用用于肽质量分析。关闭激光器并取出MALDI样品后，在第一个漏斗中背景压力逐渐降低的过程中检测到离子。恒定速率的压力降低导致不同的单电荷和双电荷的肽峰在质谱中的再现性外观采取了几秒钟后结束的MALDI分析的干液滴斑点。在完成主要MALDI分析后，观察到的离子产率以及离子的质量范围显著延迟，主要取决于第一漏斗内的背景压力。在该后电离步骤中的离子的产生在压降期间专门观察到。一个较低的基质背景和显着增加双质子化离子的相对产率的报告。这些观测结果部分符合从入口毛细管加速分离粒子到适合于基质辅助高超音速碰撞电离的动能的超音速射流模型。
Understanding the mechanisms of MALDI promises improvements in the sensitivity and specificity of many established applications in the field of mass spectrometry. This paper reports a serendipitous observation of a significant ion yield in a post-ionization experiment conducted after the sample has been removed from a standard atmospheric pressure (AP)-MALDI source. This post-ionization is interpreted in terms of collisions of microparticles moving with a hypersonic velocity into a solid surface. Calculations show that the thermal energy released during such collisions is close to that absorbed by the top matrix layer in traditional MALDI. The microparticles, containing both the matrix and analytes, could be detached from a film produced inside the inlet capillary during the sample ablation and accelerated by the flow rushing through the capillary. These observations contribute some new perspective to ion formation in both laser and laserless matrix-assisted ionization. An AP-MALDI ion source hyphenated with a three-stage high-pressure ion funnel system was utilized for peptide mass analysis. After the laser was turned off and MALDI sample was removed, ions were detected during a gradual reduction of the background pressure in the first funnel. The constant-rate pressure reduction led to the reproducible appearance of different singly- and doubly-charged peptide peaks in mass spectra taken a few seconds after the end of the MALDI analysis of a dried-droplet spot. The ion yield as well as the mass range of ions observed with a significant delay after a completion of the primary MALDI analysis depended primarily on the background pressure inside the first funnel. The production of ions in this post-ionization step was exclusively observed during the pressure drop. A lower matrix background and significant increase in relative yield of double-protonated ions are reported. The observations were partially consistent with a model of the supersonic jet from the inlet capillary accelerating detached particles to kinetic energies suitable for matrix-assisted hypersonic-velocity impact ionization.