Compelling Evidence for Lucky Survivor and Gas Phase Protonation: The Unified MALDI Analyte Protonation Mechanism
作者:Thorsten W. Jaskolla、Michael Karas
DOI:10.1007/s13361-011-0093-0
日期:2011.6.1
This work experimentally verifies and proves the two long since postulated matrix-assisted laser desorption/ionization (MALDI) analyte protonation pathways known as the Lucky Survivor and the gas phase protonation model. Experimental differentiation between the predicted mechanisms becomes possible by the use of deuterated matrix esters as MALDI matrices, which are stable under typical sample preparation conditions and generate deuteronated reagent ions, including the deuterated and deuteronated free matrix acid, only upon laser irradiation in the MALDI process. While the generation of deuteronated analyte ions proves the gas phase protonation model, the detection of protonated analytes by application of deuterated matrix compounds without acidic hydrogens proves the survival of analytes precharged from solution in accordance with the predictions from the Lucky Survivor model. The observed ratio of the two analyte ionization processes depends on the applied experimental parameters as well as the nature of analyte and matrix. Increasing laser fluences and lower matrix proton affinities favor gas phase protonation, whereas more quantitative analyte protonation in solution and intramolecular ion stabilization leads to more Lucky Survivors. The presented results allow for a deeper understanding of the fundamental processes causing analyte ionization in MALDI and may alleviate future efforts for increasing the analyte ion yield.
这项研究通过实验验证并证明了长期以来推测的两种基质辅助激光解吸/电离(MALDI)分析物质子化途径,即幸运幸存者和气相质子化模型。使用氚代基质酯作为 MALDI 基质可以在实验中区分这两种预测机制,氚代基质酯在典型的样品制备条件下是稳定的,只有在 MALDI 过程中受到激光照射时才会产生氚代试剂离子,包括氚代和氚代游离基质酸。氘化分析物离子的生成证明了气相质子化模型,而通过使用不含酸性氢的氘化基质化合物检测质子化分析物则证明了分析物从溶液中预充电后的存活,这与幸运生存者模型的预测相符。观察到的两种分析物电离过程的比例取决于应用的实验参数以及分析物和基质的性质。激光通量的增加和基质质子亲和力的降低有利于气相质子化,而溶液中更定量的分析物质子化和分子内离子稳定化则会导致更多的幸运幸存者。这些结果有助于加深对 MALDI 中分析物离子化基本过程的理解,并有助于今后提高分析物离子产率。