The Department of Chemistry and Biochemistry at the University of Oklahoma proposes the acquisition of a tandem mass spectrometer with an atmospheric pressure ionization (API) source capable of both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). The instrument will become a part of the established Analytical Services Center in the Chemistry and Biochemistry Department. This new instrument will support the activities of a growing number of bioinorganic bioorganic and biochemical research groups at the University of Oklahoma. Primary use of this instrument will be by the NIH-supported user group included in this proposal, although other users may submit samples for analysis of a time-available basis. This mass spectrometer will fill the mass analysis needs for a variety of projects including investigations into the roles of unusual oxidative metabolites of biogenic amine neurotransmitters in aberrant brain chemistry, identification of bacterial siderophores, determination of physical binding donors to metalloporphyrins containing Ru or Os, determination of the binding site for interaction of protein and RNA nucleotide, and the determination of the mechanism and stoichiometry of suicide inactivation of enzymes.