Increasing the sensitivity and information content of multi-dimensional and hyphenated LC-MS systems

The aims of this thesis were to investigate the potential of multi-dimensional separation platforms and their applicability in the analysis of complex mixtures, and to explore routes toward tackling their major drawbacks.
Chapter 1 describes the effectiveness of one-dimensional liquid chromatography and limitations in applications addressed by this technique.
In Chapter 2 the possibilities and limitations of stationary-phase-assisted modulation as a post-column focusing approach (“1,5D-LC system”) are described. “1,5D-LC” has great potential for improving the detectability of pure-compound standards.
Chapter 3 describes the development of the online comprehensive two-dimensional LC×LC-MS separation of anabolic steroids in bovine-urine samples. The proposed strategy allowed to improve the detectability of trace-level anabolic residues and resulted in clear gains in signal intensities, increased signal-to-noise ratios for steroid compounds and in a greater number of detected compounds.
In Chapter 4 a novel trapped-ion-mobility spectrometer (TIMS) is discussed. This multi-dimensional separation platform (LC-TIMS-MS) was applied for untargeted separation of lipids in human-plasma samples and was shown to provide more-detailed information in comparison with traditional LC-MS technology.
Chapter 5 describes the results of the lipidomic mapping of the human-plasma samples performed by online comprehensive two-dimensional liquid chromatography (LC×LC-MS). A comparison of LC-TIMS-MS and LC×LC-MS techniques was made in terms of the main descriptors of separation power.
Chapter 6 discusses the main achievements and also features some reflections on the future directions for development and improvement of extremely effective and accessible multi-dimensional separations.