Chemistry and Chemical Biology ETDs

Yurong Deng

Publication Date

8-27-2009

Abstract

The goal of this work is to evaluate new methods of extracting and fractionating dissolved organic matter (DOM) using liquid-liquid and solid-phase extraction (SPE), monitored by optical spectroscopy. DOM in aquatic systems from different sources was characterized by three-dimension excitation-emission matrix fluorescence spectroscopy (3DEEMS) and UV absorbance spectroscopy. UV and visible humic-like fluorescence were observed in all water samples -- humic acids (HA), fulvic acids (FA), river water, wastewater, and their fractionations. Their fluorescence centers varied with environment in the range of λex/ λem = 220-250 nm/390-460 nm for UV humic-like fluorescence (peak A) and λex/ λem = 300-340 nm/390-460 nm for visible humic-like fluorescence (peak C). pH change didnt shift maximum excitation and emission wavelengths but did change the emission intensities of peaks A and C. Peaks A and C always occur together, although relative intensities may change. Protein-like fluorescence peaks were observed in pairs with higher emission intensity at shorter wavelengths than at longer wavelengths. Tryptophan-like fluorescence (peaks T1 and T2) was observed at λex/ λem = 230 nm/356 nm and λex/ λem = 280 nm/356 nm in river water and wastewater. Tyrosine-like fluorescence (peaks S1 and S2) was observed at λex/ λem = 220 nm/309 nm and λex/ λem = 280 nm/309 nm only in a wastewater sample without extensive biological pretreatment. A new peak was observed at λex/ λem = 250-260 nm/460 nm (peak B), and overlapped with peaks A and C in all water samples and their isolates. Another peak specific to one river water sample was observed at λex/ λem =260 nm/340 (peak D) which could be mis-identified as peak T2. Partitioning of NOM into organic solvents was investigated with and without ion-pairing reagent. No extraction of either peak A or C occurred without ion-pairing reagent. Alteration of the partitioning of these two fluorophores by ion-pairing reagent and non-polar solvents enriched peak A in the aqueous phase and peak C in the organic phase. Maximum excitation and emission wavelengths shifted with the addition of ion-pairing reagent due to enhanced peak overlapping and solvent effects. Peak A is the sum of several superposed peaks rather than a simple one. Liquid-liquid extraction could separate different fluorophores but it's not easy to use. Rio Grande river water was isolated and fractionated using Solid-phase Extraction (SPE). Humic-like fluorophores (peaks A and C) could be retained by and eluted from the apolar Sep-pak C18 cartridge, Empore C18 Disk, polymeric Oasis HLB and MAX cartridges. Both humic-like fluorophores are negatively charged and visible humic-like fluorophores (peak C) are more hydrophobic than UV humic-like fluorophores (peak A). Tryptophan-like fluorophores were excluded from those sorbents and occur as neutral or positively charged hydrophilic molecules. Based on the extraction recovery, Empore C18 Disk has the highest recovery (90%) for humic-like fluorophores and Oasis HLB is good for isolating protein-like fluorophores. Oasis MAX discriminates most strongly against protein-like fluorophores, producing only humic-like fluorophores. Although protein-like fluorescence was expected to correlate with protein content of wastewater samples, protein concentration correlates strongly with SUVA and less strongly with fluorescence intensity of peak T1 and peak T2 in sewage-derived wastewater. RO membranes concentrate both humic-like and protein-like fluorophores, but protein-like fluorophores go through RO membrane more easily than humic-like fluorophores.

Language

English

Keywords

Dissolved organic matter, fluorophores, separation

Document Type

Dissertation

Degree Name

Chemistry and Chemical Biology

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

Howe, Kerry

Second Committee Member

Keller, David

Third Committee Member

Wang, wei

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