A Comparative Study Performed on Two Ambient Ionization Techniques: Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) and Easy Ambient Sonic Spray Ionization Mass Spectrometry (EASI-MS)

Main project of my master’s thesis involved comparison between two sister methods: desorption electrospray ionization mass spectrometry (DESI−MS) and easy ambient ionization mass spectrometry (EASI−MS). These methods are compared in terms of spatial resolution, limits of detection and imaging capabilities. Their applicability in forensic science was further explored by comparing the MS/MS imaging capabilities. Under the same experimental conditions, we found that both DESI and EASI−MS have similar spray spot size resulting in similar spatial resolution. For the limits of detection (LOD) experiment, the LOD of DESI−MS was found to be lower than EASI−MS by an order of magnitude. When we compared the mass spectra and the chemical images of DESI and EASI, we found that both methods produce similar chemical specificity. When the spectra were carefully inspected, a reduction in signal intensity was observed for EASI−MS compared to DESI−MS demonstrating that the sensitivity of DESI−MS is higher than EASI−MS. Other projects involved characterization of zebra fish tissue system made up of bile salts, phospholipids and fatty acids. By mapping the spatial distribution of these ions, 2D chemical images of organs such as the stomach, the nervous system and the whole body zebra fish were created. I also studied if matrix can impact ionization of proteins by DESI−MS. The aim was to improve the poor desorption of proteins from the surface of DESI−MS. We concluded that the matrix neither increase nor decreases the ionization efficiency of proteins by DESI−MS.