Vienna University of Technology, Institute of Chemical Technologies and Analytics, Vienna, Austria.
Rapid Commun Mass Spectrom. 2009 Dec;23(24):3917-27. doi: 10.1002/rcm.4326.
The aim of this study was to investigate the utility of ion trap mass spectrometry (ITMS) in combination with the two desorption/ionization methods, electrospray (ESI) and atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI), for the detection of antioxidants which are applied in lubricants. These experiments should form the base for future investigations of antioxidants in tribologically formed thin layers on the surface of frictional systems. Seventeen different antioxidants were selected out of the group of hindered phenolic and aromatic aminic compounds. Practically all antioxidants could be characterized by positive ion ESI- and AP-MALDI-ITMS, forming various types/species of molecular ions (e.g. [M]+*, [M+H]+, [M+Na]+ or [M-2H+H]+). A few compounds could be analyzed by negative ion ESI-MS, too, but none by negative ion AP-MALDI-MS. The influence of target materials in AP-MALDI-MS (gold- and titanium nitride (TiN)-covered stainless steel, micro-diamond-covered hard metal, hand-polished and sand-blasted stainless steel targets) with respect to the molecular ion intensity and type of molecular ion of two selected antioxidants was evaluated. The surface properties are of particular interest because in friction tests different materials with different surface characteristics are used. However, the MS results indicate that optimal target surfaces have to be found for individual antioxidants in AP-MALDI-MS but in general smooth surfaces were superior to rough surfaces. Finally the gold-covered stainless steel MALDI target provided the best mass spectra and was selected for all the antioxidants investigated.
本研究旨在探讨离子阱质谱（ITMS）与两种解吸/电离方法（电喷雾（ESI）和大气压基质辅助激光解吸/电离（AP-MALDI））相结合，用于检测应用于润滑剂中的抗氧化剂的实用性。这些实验将为未来在摩擦系统表面的摩擦形成的薄层中研究抗氧化剂奠定基础。从受阻酚和芳香胺化合物组中选择了 17 种不同的抗氧化剂。实际上，所有的抗氧化剂都可以通过正离子 ESI 和 AP-MALDI-ITMS 来表征，形成各种类型/种类的分子离子（例如 [M]+*、[M+H]+、[M+Na]+或[M-2H+H]+）。少数化合物也可以通过负离子 ESI-MS 进行分析，但没有一种可以通过负离子 AP-MALDI-MS 进行分析。评估了 AP-MALDI-MS 中目标材料（镀金和氮化钛（TiN）覆盖的不锈钢、微金刚石覆盖的硬质合金、手工抛光和喷砂不锈钢靶材）对两种选定抗氧化剂的分子离子强度和分子离子类型的影响。表面性质特别重要，因为在摩擦试验中使用了具有不同表面特性的不同材料。然而，MS 结果表明，在 AP-MALDI-MS 中，需要为每种抗氧化剂找到最佳的目标表面，但通常来说，光滑表面优于粗糙表面。最后，镀金不锈钢 MALDI 靶材提供了最佳的质谱图，并被选为所有研究的抗氧化剂。
