Molecular Characterizaiton Of Dissolved Organic Matter By Fourier Transform Ion Cyclotron Resonance Mass Spectrometry:Methodology And Application

Dissolved organic matter?DOM?is one of the most complex naturally occurring mixtures in aqueous systems and is the main organic contaminants in various wastewaters.However,the molecular composition of DOM is still not clear.The present dissertation establishes a standard method to characterize the chemical composition of various DOMs on molecular level by using Fourier transform ion cyclotron resonance mass spectrometry?FT-ICR MS?.Ionization process,ion transportation process,and ICR cell detection were regulated.After quantitative constraints on peak shapes,molecular weight range of FT-ICR mass spectrum,a standard method was developed for molecular characterization of DOM for negative-ion ESI FT-ICR MS.The method has good repeatability and reproducibility,and could be applied to characterize molecular composition of various DOM with different sources and times,which provide a methodological support for the research in environmental science and geochemistry and the technology development in environmental engineering.Systematic comparison on eight typical DOMs was performed through molecular compositional characterization.CHO,CHON,CHOS,and CHONS class species which can be categorized into totally 127 types of heteroatom species were identified in all samples.Natural DOM was dominant with CHO class species,including O₂-O₂₃,while the center of the normal distribution was about O₉-O₁₂.The molecular oxidation degree orders of DOMs were:forest soil>paddy soil>river water>lake water>seawater>ground water.CHON compounds generally contain 1-5 nitrogen atoms.The paddy soil DOM has the highest nitrogen content.The relative abundance of nitrogen compounds in the seawater and the lake water was higher than that in the river water.CHOS compounds generally contain one sulfur atom.The sulfur content in domestic wastewater DOM is higher than that in natural DOMs.The composition of DOM from refinery wastewater is most complex.The content of sulfur and nitrogen compounds in the refinery wastewater was higher than that of the environmental water,while the oxygen content and molecular condensation degree of the compounds in the refinery wastewaters was lower.DOMs in Pearl River Estuary along environmental gradient were analyzed,and molecular composition and spatial distribution were revealed.Terrigenous organic matter is gradually diluted and degraded during the migration from the river to the sea.The carboxylic-rich alicyclic molecules?CRAM?were accumulated in the marine DOM pool.The composition of the DOM shows a gradual variation with the salinity/spatial changes.However,the mass spectral distributions of DOM from the Pearl River Estuary are slightly different from the DOM of other estuaries with unaffected natural environment.Mass spectrometry results show that the detailed molecular composition of DOM is crucial for its origin and fate in the estuary area.Various ionization techniques were coupled with FT-ICR MS to characterize the molecular composition of DOM in refinery wastewater.The compounds in wastewater DOM are hydrocarbons,naphthenic acids,phenols,esters,ketones,basic nitrogen,non-basic nitrogen,and sulfur compounds.No class species have been completely removed during water treatment,while compounds with lower fewer oxygen atoms are preferentially removed.