Development of Novel Methods for Characterization of Complex Organic Mixtures By Liquid Chromatography and Raman Spectroscopy

Abstract

ABSTRACT DEVELOPMENT OF NOVEL METHODS FOR CHARACTERIZATION OF COMPLEX ORGANIC MIXTURES BY LIQUID CHROMATOGRAPHY AND RAMAN SPECTROSCOPY by Veronica Marco Alvarez The University of Wisconsin-Milwaukee, 2014 Under the Supervision of Professor Joseph H. Aldstadt III The development of methods for the study of Humic Acids (HAs) and related substances is described. In the first part, a reversed-phase liquid chromatography (RP-LC) instrument was designed, fabricated, and a method for the separation of HAs was optimized for application as the second dimension in a two-dimensional LC (LCxLC) system. The optimized method for the RP-LC was used in the study of amino acid mixtures and HA standard solutions. The RP-LC used a monolithic disk in which the stationary phase was composed of butyl (C4) functional groups. The method had the following conditions: 100 µL injection volume, 1.0 mL/min flow rate, 30:70 acetonitrile:water (pH = 7.00) mobile phase, and fluorescence detection (λex = 257 nm, λex = 310 nm). Several HA fractions from solid-phase extraction separations were examined as a means to simplify the HA standard and their spectra were compared to the characteristic peaks found for HAs in the literature. The next step in this work is to integrate the RP-LC method into the LCxLC system. In the second part of this thesis, the characterization of two natural varnishes -- Linseed Oil and Chinawood Oil-- was studied by accelerated ageing experiments and Fourier Transform Raman Spectroscopy (FT Raman). An ageing chamber designed in our group for a previous investigation was modified to perform the ageing experiments. Two factors were studied over a range of time periods: heat and ultraviolet light. Thermal studies were conducted from 25ᵒC to 210ᵒC while the time periods ranged from 2 to 170 hr. A direct correlation was found between the changes in the vibrational bands that were observed in the FT Raman spectra and the observation of overt physical changes in the samples. Based upon these data, several reaction mechanisms for the decomposition of the varnishes were proposed. The FT Raman method may also be applied in the future to fractions collected from the LCxLC system for a more detailed off-line characterization of the molecular structures that are present.