Generation of multiply charged peptides and proteins from glycerol-based matrices using lasers with ultraviolet, visible and near-infrared wavelengths and an atmospheric pressure ion source
Generation of multiply charged peptides and proteins from glycerol-based matrices using lasers with ultraviolet, visible and near-infrared wavelengths and an atmospheric pressure ion source
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DOI：
10.1016/j.ijms.2016.11.007
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发表时间：
2017-05-01
影响因子：
1.8
通讯作者：
Dreisewerd, Klaus
中科院分区：
文献类型：
--
作者：
Koch, Annika;Schnapp, Andreas;Dreisewerd, Klaus
传统的基质辅助激光解吸/电离质谱法（MALDI-MS）的特点是主要产生单电荷的分析物离子。最近的研究表明，如果利用液体甘油基基质系统，并通过加热的离子入口管实现AP-真空转移，则常压MALDI离子源可以产生高电荷态的肽和小蛋白质[R]。克拉默，A.皮尔克尔，F.希伦坎普，K.德莱泽沃德，安德鲁。化学。Int。编辑，52(2013)2364-2367]。本文采用该AP离子源，利用光学参量振荡器（OPO）激光器研究了260 ~ 1080 nm范围内离子产生的波长依赖性。研究了三种具有不同光吸收特性的基质体系：三氟乙酸（TFA）混合无吸收甘油和2,4-或2,5-二羟基苯甲酸混合甘油作为两种经典紫外- maldi基质。在含有发色团的基质体系具有最低光吸收的激光波长下，多次带电肽的离子产率始终是最高的。使用1064 nm的Nd: yag激光器（或调谐到类似波长的OPO激光器），透明甘油/TFA混合物甚至达到了最佳灵敏度。用吸收和透明样品衬底的实验证明了衬底吸收的参与。与AP离子源获得的结果相反，使用相同的基质系统与标准oMALDI2Tm离子源，在毫巴的精细真空下工作，没有进气管，观察到相反的波长依赖性。或者换句话说，就像在标准UV-MALDI中一样，在这些条件下，激光激发波长对应于矩阵的高吸收率，获得了最高的分析物离子产率。因此，我们的研究结果指出了两种离子源几何形状和激光激发制度下完全不同的解吸/电离过程。我们假设，在AP情况下，材料烧蚀包括低能量激光散裂，热传递毛细管中小液滴的快速蒸发电离是电荷产生的原因。从分析的角度来看，对于被测分析物（质量范围从1到17 kDa），具有电荷态的多电荷肽和蛋白质离子的产生几乎完全类似于纳米电喷雾电离（ESI）产生的电荷态，可以促进基于激光的离子源与质量分析仪的耦合，例如正交提取飞行时间（QTOF）仪器或轨道阱，这些仪器仅具有有限的m/z范围。(C) 2016 Elsevier B.V.版权所有
Conventional matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is characterized by the predominant generation of singly charged analyte ions. Recent studies demonstrated that high charge states of peptides and small proteins can be produced with an atmospheric pressure (AP) MALDI ion source if liquid glycerol-based matrix systems are utilized and the AP-vacuum transfer is realized via a heated ion inlet tube [R. Cramer, A. Pirkl, F. Hillenkamp, K. Dreisewerd, Angew. Chem. Int. Ed. 52 (2013) 2364-2367]. Here, we used this AP ion source and employed an optical parametric oscillator (OPO) laser to study the wavelength dependence of the ion generation between 260 and 1080 nm. Three matrix systems with different optical absorption characteristics were investigated: non-absorbing glycerol mixed with trifluoroacetic acid (TFA) and glycerol mixed with either 2,4-or 2,5-dihydroxybenzoic acids as two classical UV-MALDI matrices. The highest ion yields of multiply charged peptides were consistently obtained at laser wavelengths for which the chromophore-containing matrix systems exhibited the lowest optical absorption. Best sensitivities were even achieved with the transparent glycerol/TFA mixture and by use of a Nd:YAG-laser operated at 1064 nm (or with the OPO laser tuned to a similar wavelength). Experiments with absorbing and transparent sample substrates demonstrated the involvement of substrate absorption. In contrast to the results obtained with the AP ion source, using the same matrix systems in combination with a standard oMALDI2Tm ion source, operated at a fine vacuum of mbar and without an inlet tube, the inverse wavelength dependence was observed. Or in other words, like in standard UV-MALDI under these conditions the highest analyte ion yields were obtained for laser excitation wavelengths corresponding to a high absorptivity of the matrix. Our findings thus point to completely different desorption/ionization processes with the two ion source geometries and laser excitation regimes. We hypothesize that for the AP case the material ablation comprises low-energy laser spallation and that rapid evaporative ionization of small droplets in the heated transfer capillary is responsible for charge production. From an analytical point of view, the production of multiply -charged peptide and protein ions with charge states that for the tested analytes (ranging by mass from 1 to 17 kDa) almost fully resembled those generated by nano-electrospray ionization (ESI) could facilitate the coupling of laser-based ion sources with mass analyzers, such as orthogonal-extracting time-of-flight (QTOF) instruments or orbitraps which exhibit only limited m/z ranges. (C) 2016 Elsevier B.V. All rights reserved.