Nontargeted discovery of xenobiotics in human urine by MALDI-TOF/TOF-MS

• Online Access: http://hdl.handle.net/2047/D20285808

In this dissertation research, nontargeted analysis of the urine metabolome, including xenobiotics, was studied using LC (Liquid Chromatography)-MALDI (Matrix Assisted Laser Desorption Ionization) MS (Mass Spectrometry) techniques. MALDI is a sensitive soft ionization MS technique that has been mainly used to analyze large molecules such as peptides, proteins, and nucleic acids. Here, MALDI MS methods were employed for detection of urine metabolites. To increase the recovery of nonpolar metabolites, a novel porous extraction paddle (PEP) was validated with co-workers and used for urine extraction. A method for sample preparation including UHPLC (Ultra High-Performance Liquid Chromatography) was optimized to facilitate detection of nonpolar urine sulfate metabolites by MALDI MS. Using this approach, the detection coverage of such compounds was greatly expanded as compared to prior methods. Detection of 1129 MS precursor ions corresponding to putative sulfate and glucuronide metabolites was achieved. Combining MS and MS/MS experiments, a strategy was developed for tentative identification of the detected metabolites. This led to the first nontargeted analysis of environmental contaminants in urine. It was shown that the detection sensitivity of positive-mode MALDI MS can be enhanced using enzymatic deconjugation and cationic tagging methods. Also, an evaporative derivatization method was developed to increase the sensitivity of negative-mode MALDI MS for detection of phenolic compounds. Overall, through careful method development and optimization, the usefulness of LC-MALDI MS as an analytical platform for the measurement of the urine nonpolar metabolome, including urinary xenobiotics, has been extended.