ESI ion trap-HPLC combines the considerable selectivity and sensitivity of electrospray ionization (ESI) mass spectrometry with fine analytical separations that can serve the research purposes of organic and bioorganic chemists. The four named investigators at the Department of Chemistry at UC Davis manage research that encompasses analytical, synthetic organic and bioorganic chemistry which are critically dependent upon access to MS. In recent years, the evolution of individual faculty research programs has brought demands for analytical methods that have outpaced available instrumentation. In order to meet the needs of four major users and various minor users in the Department of Chemistry, UC Davis, we request an HPLC -ESI ion trap mass spectrometer which will accommodate a range of research experiments involving small molecules (MW <2,000) to small proteins (MW<20,000) and provide new capabilities in soft ionization techniques in line with analytical chromatography. The critical need and common research theme for each major user is a need for real-time MS measurements of time-dependent phenomena (kinetics, liability studies, or analysis of separation & isolation of natural products that cannot be effectively accommodated by submission to routine MS services. The four major users manage a total of 6 major NIH RO1 or PO1 grants. Carlito Lebrilla studies the structures of sulfated and non-sulfated branched oligosaccharides using ESI MS/MS spectrometry. Claude Meares characterizes the structure of peptides chemically conjugated to metal chelating groups. Three natural products chemistry programs will be supported. Tadeusz F. Molinski studies the isolation and structure elucidation of biologically active small molecule components of marine invertebrates and the consensus binding site of the Ca2+ channel agonist, bastadin-5 with the RyR1 channel. Ben Shen investigates the molecular genetics, enzymology and temporal aspects of modular polyketide biosynthesis. The proportion of proposed instrument time allocated to the four major users will be 80% with the balance of the time made available to identified minor users within the department of chemistry.