Analysis of Oxidized Phospholipids by MALDI Mass Spectrometry Using 6-Aza-2-thiothymine Together with Matrix Additives and Disposable Target Surfaces

6-Aza-2-thiothymine (An) is introduced as novel matrix system for the analysis of oxidized phospholipids (OxPLs) by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). A systematic evaluation comparing different established and novel matrix substances, especially 2,4,6-THAP matrix (Stubiger, G.; Belgacem O. Anal. Chem. 2007, 79, 3206-3213) as reference compound for phospholipid analysis, and specific matrix additives was performed. Thereby, ATT turned out to be the reagent of choice for MALDI analysis of major biologically relevant OxPL classes (e.g., OxPC, OxPE, and OxPS) in positive and negative ionization mode. ATT used together with specific chaotropic reagents at low concentration (0.5-2 mM) acting as OxPL ionization enhancers revealed an excellent comatrix system for application with MALDI instrument types employing UV- and Nd:YAG laser systems (337 and 355 nm). Moreover, disposable MALDI targets surfaces with specific physicochemical properties (e.g., metallized glass or polymeric substrates) were revealed as superior over stainless steel in terms of reduced chemical background noise (similar to 10-fold better S/N ratios), increased mass spectral reproducibility, and enhanced sensitivity (LOD similar to 250-500 fg on target). The combination of these parameters offers a significant advantage for highly sensitive OxPL profiling by MALDI-MS of biological samples (e.g., human plasma) at trace levels.