Browsing by Author "Aalto, Henni"

Lipids are fat soluble compounds that are derived from living tissues. Lipids have many important physiological functions. Developing methods for efficient lipid analysis is important since lipids can function as biomarkers in diseases. Additionally these methods can be used for the discovery of the biological processes of disease development. Lipids comprise of molecules with different polarity and structure. Several mass spectrometric ionization methods have been used in the analysis of lipids but they usually require sample preparation prior to the analysis. Desorption electrospray ionization-mass spectrometry (DESI-MS) and desorption photoionization-mass spectrometry (DAPPI-MS) are novel ionization methods that allow sample analysis straight from the matrix, such as tissue, usually without any sample preparation. DESI-MS has already been used in the analysis of different lipids, but DAPPI-MS has only been used in the analysis of steroids. The ionization of a range of lipid compounds (phospholipids, triglycerides, fat soluble vitamins, fatty acids, and steroids) by DAPPI-MS and DESI-MS was studied. Analysis conditions were optimized for all the different lipid classes with both DAPPI and DESI using standard samples. Some lipids were also analysed straight from pharmaceutical preparations. There were differences in the suitabilities of DAPPI-MS and DESI-MS for the ionization of different lipid classes. DAPPI-MS worked well for the ionization of nonpolar lipids like triglycerides, vitamins and fatty acids, but the phospholipids fragmented in the DAPPI-MS process and showed no molecular ion. Previous studies have shown that DESI-MS works well in the ionization of phospholipids, and this study showed that it works reasonably well for other lipid groups as well, with the exception of some of the nonpolar lipids. New knowledge was acquired especially about the suitability of DAPPI-MS for the analysis of different lipids. Based on the results it can be said that DAPPI-MS works equally well or better than DESI-MS in the ionization of most lipid classes. The DAPPI method should still be further developed so that phospholipids, which are very important lipids in human physiology, could be analysed by DAPPI-MS. As lipids were not analysed straight from a tissue sample, there are no conclusions about the suitability of DAPPI-MS for the analysis of lipids straight from tissue samples.