Spatial metabolomics using Surface Sampling Capillary Electrophoresis Mass Spectrometry  : New tool for direct surface sampling chemical analysis of biological samples

Sammanfattning: Analytical surface sampling tools enable direct chemical studies of solid biological samples, including morphologically diverse tissue, and provide both fast chemical analysis with minimum sample preparation and information about molecular spatial distribution. Spatially resolved investigations of tissue sections could help to reveal pathological mechanisms at specific tissue locations. Mass spectrometry imaging (MSI) is a valuable method for direct tissue analysis that can give a full molecular profile of heterogeneous biological in a short period of time. However, MSI is not always capable of identifying isomeric and isobaric species, especially for low-weight metabolites. Moreover, the complex chemical matrix of biological samples significantly influences the performance of MSI, including introducing artefacts such as ion suppression. Therefore, separation by liquid chromatography or capillary electrophoresis prior mass spectrometric detection is beneficial to mitigate such artefacts and increase sensitivity. Recently, the new setup for surface sampling capillary electrophoresis mass spectrometry (SS-CE-MS) was presented that enables direct sampling from a tissue location followed by separation and mass spectrometric detection. This thesis is aimed to show the developments and improvements of SS-CE-MS along with applications of quantitative spatial metabolomics.Paper I demonstrates SS-CE-MS using a sheath liquid interface to the MS and its robustness and reproducibility both for the injection process and the connection to mass spectrometer. Analysis of small polar molecules, lipids, and proteins in both tissue and blood samples is described in addition to an increased throughput using multisegmented electrokinetic injection.In Paper II five quantitative approaches for SS-CE-MS were developed and evaluated. Off-line one-point calibration was found to be optimal for tissue analysis and further used for mapping metabolites, including isomeric species, in four regions of rat brain. Specifically, aromatic amino acids were found decreased in cortex and the isomers valine and leucine were more abundant than their isomers betaine and isoleucine, respectively.Overall, this thesis shows SS-CE-MS as promising new quantitative method for future applications to healthy and pathological tissue investigation.