The objective of this proposal is to improve analytical performance of Desorption Electrospray Ionization (DESI) coupled to a high resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR-MS) and gain more insight into the DESI mechanism and underlying processes. DESI is a novel ionization method, that combines features of electrospray ionization (ESI) with those of the family of desorption ionization (DI) methods. The DESI experiment allows molecules present on surfaces to be analyzed by mass spectrometry without requiring the sample to be introduced into the vacuum system of the mass spectrometer. DESI differentiates itself from other DI methods in mass spectrometry because the sample can be analyzed outside the mass spectrometer in an open laboratory environment. There is virtually no sample handling in DESI and no ionization matrix needs to be added to the sample; the sample is sprayed with charged microdroplets of solvent (e.g. water, methanol etc.), delivered by a simply modified electrospray emitter (electrosonic electrospray or ESSI). DESI proved itself to be a useful tool in a very wide range of disciplines from traditional chemical and pharmaceutical process and quality control to more exotic applications including dactyloscopy and tissue imaging. Most of the interest in DESI inside mass spectrometry community is chiefly in the analytical applications area. There have only been handful reports focused on DESI theory and mechanism. Thus, the fundamental processes in DESI are not fully understood and despite many advantages DESI also suffers limitations, especially relatively poor Limit of Detection (LOD) compared to competing mass spectrometry techniques. The analytical figures of merit will play more significant role in the near future because two dimensional DESI imaging is currently being introduced. That is why this proposal is focused on investigation of fundamental surface processes in DESI and its overall improvement.