The analysis of aqueous mixtures using liquid chromatography: electrospray mass spectrometry

Johnson, Steven
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The focus of this dissertation is the use of chromatographic methods coupled with electrospray mass spectrometry (ES-MS) for the determination of both organic and inorganic compounds in aqueous solutions;The combination of liquid chromatography (LC) methods and ES-MS offers one of the foremost methods for determining compounds in complex aqueous solutions. In this work, LC-ES-MS methods are devised using ion exclusion chromatography, reversed phase chromatography, and ion exchange chromatography, as well as capillary electrophoresis (CE). For an aqueous sample, these LC-ES-MS and CE-ES-MS techniques require no sample preparation or analyte derivitization, which makes it possible to observe a wide variety of analytes as they exist in solution. The majority of this work focuses on the use of LC-ES-MS for the determination of unknown products and intermediates formed during electrochemical incineration (ECI), an experimental waste remediation process;Ion exclusion chromatography (IEC) was used to study small carboxylic acids. The effect of pH, solvent composition, sheath gas make-up, and presence of concentrated matrix was observed. Detection limits were found to range from 40 to 200 ppb for the direct infusion of most carboxylic acids and from 2 to 8 ppm for IEC-ES-MS;The ECI of benzoquinone is studied using IEC-ES-MS. Unknown intermediates and products are identified and observed as a function of ECI time. The ECI procedure is described in detail and electrode efficiency is evaluated. Mechanisms are also proposed for the production of maleic, succinic, malonic, and acetic acids;The ECI of 4-chlorophenol is observed using reversed phase liquid chromatography--ES-MS to study aromatic compounds, and ion exchange chromatography--ES-MS for organic and inorganic ions. The majority of this work is accomplished with ion exchange chromatography--ES-MS, which requires a suppressor to remove sodium ions from the mobile phase. The system has proven effective in the identification of a wide range of unknown compounds in complex aqueous solutions. Detection limits range from 50 ppb to 4 ppm;Capillary electrophoresis was also studied as a possible separation method coupled to an ES-MS. Different mobile phases are examined and tested with CE-ES-MS for the determination of carboxylic acids. Detection limits range between 1 and 10 ppm.

Chemistry, Analytical chemistry