Ross AR, Ikonomou MG, Orians KJ
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1.
J Mass Spectrom. 2000 Aug;35(8):981-9. doi: 10.1002/1096-9888(200008)35:8<981::AID-JMS26>3.0.CO;2-P.
The utility of electrospray ionization mass spectrometry (ESI-MS) for characterizing dissolved metal species has generated considerable interest in the use of this technique for metal speciation. However, the development of accurate speciation methods based on ESI-MS requires a detailed understanding of the mechanisms by which dissolved metal species are ionized during electrospray. We report how the analysis of alkali and alkaline earth metal species provides new information about some of the processes that affect electrospray ion yield. Selected metal ions and organic ligands were combined in 50 : 50 water-acetonitrile buffered with acetic acid or ammonium acetate and analyzed by flow injection ESI-MS using mild electrospray conditions. Species formed by alkali metal ions with thiol and oxygen-donating ligands were detected in acidic and neutral pH solutions. Electrochemical oxidation of N, N-diethyldithiocarbamate and glutathione during electrospray was indicated by detection of the corresponding disulfides as protonated or alkali metal species. The extent of ligand oxidation depended on solution pH and the dissociation constant of the thiol group. Tandem mass spectrometric experiments suggested that radical cations such as NaL (where L=N,N-diethyldithiocarbamate) can be generated by in-source fragmentation of disulfide species. Greater complexation of alkali metals at neutral pH was indicated by a corresponding decrease in the relative abundance of the free metal ion. The number of alkali metal ions bound by glutathione and phthalic acid also increased with increasing pH, in accordance with thermodynamic equilibrium theory. Alkaline earth metal species were detected only in acidic solutions, the absence of 8-hydroxyquinoline complexes being attributed to their relative instability and subsequent dissociation during electrospray. Hence, accurate speciation by ESI-MS depends on experimental conditions and the intrinsic properties of each analyte. Copyright 2000 John Wiley & Sons, Ltd.
电喷雾电离质谱法（ESI-MS）在表征溶解态金属物种方面的实用性，引发了人们对将该技术用于金属形态分析的浓厚兴趣。然而，基于ESI-MS开发准确的形态分析方法需要详细了解溶解态金属物种在电喷雾过程中被电离的机制。我们报告了碱金属和碱土金属物种的分析如何为影响电喷雾离子产率的一些过程提供新信息。将选定的金属离子和有机配体在由乙酸或乙酸铵缓冲的50:50水 - 乙腈中混合，并使用温和的电喷雾条件通过流动注射ESI-MS进行分析。在酸性和中性pH溶液中检测到了由碱金属离子与硫醇和供氧化合物形成的物种。通过检测相应的二硫化物作为质子化或碱金属物种，表明了电喷雾过程中N，N - 二乙基二硫代氨基甲酸盐和谷胱甘肽的电化学氧化。配体氧化程度取决于溶液pH值和硫醇基团的解离常数。串联质谱实验表明，诸如NaL（其中L = N，N - 二乙基二硫代氨基甲酸盐）之类的自由基阳离子可通过二硫化物物种的源内裂解产生。中性pH下碱金属的络合作用增强，这表现为游离金属离子相对丰度相应降低。根据热力学平衡理论，谷胱甘肽和邻苯二甲酸结合的碱金属离子数量也随pH值升高而增加。仅在酸性溶液中检测到碱土金属物种，8 - 羟基喹啉配合物的缺失归因于它们相对不稳定以及在电喷雾过程中随后的解离。因此，通过ESI-MS进行准确的形态分析取决于实验条件和每种分析物的固有特性。版权所有2000 John Wiley & Sons, Ltd.
