Relative importance of basicity in the gas phase and in solution for determining selectivity in electrospray ionization mass spectrometry
Relative importance of basicity in the gas phase and in solution for determining selectivity in electrospray ionization mass spectrometry
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DOI：
10.1016/j.jasms.2008.01.003
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发表时间：
2008-05-01
影响因子：
3.2
通讯作者：
Cech, Nadja B.
中科院分区：
文献类型：
--
作者：
Ehrmann, Brandie M.;Henriksen, Trine;Cech, Nadja B.
电喷雾电离质谱法是测定小分子的一项极其重要的技术，但其在这一目的上的应用因其选择性而变得复杂。对于碱性分析物的正离子 EST-MS 分析，一些研究人员指出了分析物碱度作为选择性来源的重要性。然而，目前尚不清楚气相中的碱性还是溶液中的碱性对于确定响应性最终最重要。这些研究的目的是调查溶液和气相中碱度作为预测正离子 EST-MS 分析选择性的因素的相对重要性。比较了多种可质子化分析物在两种不同溶剂（纯甲醇和含 0.5% 乙酸的甲醇）中的 EST-MS 响应。观察到分析物 pK(b) 和电喷雾响应之间存在相关性。然而，具有非常高 pK(b) 值的分析物的响应显着高于基于质子化形式或溶液中分析物浓度的预期，并且这种较高的响应似乎不是由气体普适质子转移反应引起的。尽管所有研究的分析物都具有比溶剂更高的气相碱度，但它们的相对响应并不由气相碱度决定。与纯甲醇相比，在酸化甲醇中研究的所有分析物均观察到更高的响应，并且这种更高的响应对于弱碱性分析物最为明显。这些发现支持使用分析物 pKb 来开发小分子 ESI-MS 分析的合理方法。
Electrospray ionization mass spectrometry is a critically important technique for the determination of small molecules, but its application for this purpose is complicated by its selectivity. For positive ion EST-MS analysis of basic analytes, several investigators have pointed to the importance of analyte basicity as a source of selectivity. Currently, however, it is not known whether basicity in the gas phase or in solution is ultimately most important in determining responsiveness. The objective of these studies was to investigate the relative importance of basicity in solution and in the gas phase as factors that predict selectivity in positive ion EST-MS analysis. EST-MS response was compared for a diverse series of protonatable analytes in two different solvents, neat methanol and methanol with 0.5% acetic acid. A correlation was observed between analyte pK(b) and electrospray response. However, the response for the analytes with very high pK(b) values was significantly higher than would be expected based on concentration of the protonated form or the analyte in solution, and this higher response did not appear to result from gas-pliase proton transfer reactions. Although all of the analytes investigated had higher gas-phase basicities than the solvent, their relative responses were not dictated by gas-phase basicity. Higher response was observed for all of the analytes studied in acidified methanol compared with neat methanol, and this higher response was most pronounced for weakly basic analytes. These findings support the use of analyte pKb for rational method development in ESI-MS analysis of small molecules.