Development Of Pretreatment Methods For Molecular Characterization Of Chemical Sewage Dissolved Organic Matter

The category and content of dissolved organic matter(DOM)in chemical sewage are the key indicators to determine its treatment process.However,the understanding of the composition of DOM in chemical sewage is not comprehensive yet.It is of great significance to establish a pretreatment method oriented to molecular characterization for its comprehensive measurement.In this paper,a mixed extraction method based on polar extraction and ion exchange extraction was established by investigating the solid phase extraction(SPE)method.A pretreatment method for molecular analysis of Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)was developed.The molecular composition of strong polar dissolved organic matter in natural water and chemical wastewater was characterized.The main contents include:The separation of DOM from water and the information of the molecular composition of each component were investigated by segmented elution and series solid phase extraction.It was found that the traditional one-step elution could result in a considerable amount of organic matter not effectively retained or inhibited by ionization during mass spectrometry analysis because it could not be separated.The main types of compounds that missed were NO and NOS,which were mainly lipids and tannins.Segmented elution could effectively avoid the loss of this part of organic matter.A series of solid phase extraction methods were studied and it was found that SPE cartridges of the same type and different sorbent still retained DOM specificity due to the difference of functional groups.C18 tended to retain low O/C,high H/C and weak polarity lipid substances,while HLB tended to retain high O/C,low H/C and strong polarity tannic acid substances.Series solid phase extraction can supplement the retention of these substances lost from PPL.Based on the mechanism of anion-cation exchange separation,the strong polar components in DOM which are difficult to extract and retain can be retained and separated.Combined with FT-ICR MS and 3DEEM,the strong polar DOM can be effectively analyzed and identified.The results of separation and analysis of DOM in natural water show that the strong polar acid-base components have certain specificity in the type of compounds and molecular composition.Among them,the hydrophilic acidic substances are mainly tannic acid.In view of the higher O/C and lower H/C distribution,it is speculated that this part contains more carboxylic hydrophilic groups,which makes it more hydrophilic.Hydrophilic alkaline substances mainly consist of amides,and more amino functional groups may give them stronger hydrophilicity.Combining with three-dimensional fluorescence spectroscopy analysis,it can be found that,unlike the hydrophobic components,the main hydrophilic acids and alkaline substances are tryptophan and tyrosine,which of both are hydrophobic Amino Acids.Mixed solid phase extraction(SPE)was applied to the chemical sewage system.The hydrophobic and hydrophilic properties of SPE were characterized.It was found that the hydrophilic content of organic matter in chemical wastewater was higher than that of natural organic matter,which might be due to the refractory substances in chemical wastewater.Although the distribution of its main components is similar to that of natural organic matter,tannins with high O/C ratio and lipids with high H/C ratio are dominant.However,its overall distribution shows lower O/C and higher H/C.At the same time,more unsaturated hydrocarbons and carbohydrates are found,which indicates that the molecular structure and composition of DOM in chemical wastewater are different from that in natural water.The hydrocarbons and carbohydrates in DOM may come from sewage itself and belong to dissolved organic matter which is difficult to extract.In this paper,the molecular composition of dissolved organic matter in chemical sewage is more comprehensively understood.By comparing with natural organic matter,it can be used as a method to trace the source of pollutants and provide data support for water quality analysis and water treatment process development.The separation and analysis method can also be used in the study of other chemical wastewater,which provides a methodological basis and theoretical basis for environmental risk assessment and treatment process design of chemical wastewater.