Large-Scale Isolation And Molecular Level Characterization Of Marine DOM

The marine dissolved organic matter(DOM)is one of the largest activated carbon pools in the world and it is also an important part of the global carbon cycle.Although the research on the origin,composition and circulation of marine DOM has made great progress,the research on its chemical structure has been blocked,mainly due to the chemical complexity of DOM itself and the lack of suitable large-volume extraction methods.The quantity and purity of DOM samples are difficult to meet the needs of multiple characterization methods.In this paper,By applying the three methods to seawater samples,the efficiencies of XAD,PPL and RO/ED DOM isolation were compared.The main contents include:1.4 g DOM were obtained from 1307 L seawater by utilizing tandem columns of DAX-8 and XAD-4 resins.The extraction rate of DOM was about 10 mg/h.Four fractions,namely hydrophobic acidic component(HOA),a hydrophilic acidic component(HIA),a hydrophobic neutral component(HON),and a hydrophilic neutral component(HIN)were extracted.The recovery rate of the four fractions is equivalent,about 10-15%.They were characterized in macroscopic properties and molecular level by elemental analysis,three-dimensional fluorescence and Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS).The PPL solid phase extraction method(SPE)was optimized and its reuse performance was evaluated.4225 L seawater samples were processed successively,and a total of 3.6 g DOM solid samples were obtained with extraction rate about 25 mg/h,the chemical properties of the DOM sample are similar to the acidic components extracted by XAD method.At the same time,a semi-automatic DOM large volume enrichment device was established to increase the DOM extraction speed.In order to obtain a more complete marine solid DOM sample,the SPE series reverse osmosis coupled electrodialysis(RO/ED)extraction method was used,and 0.28g(SPE)and 0.21 g(RO/ED)DOM samples were extracted from 200 L of seawater in Yantai offshore.And elemental analysis,three-dimensional fluorescence,infrared spectroscopy and ultra-high resolution mass spectrometry were used to analyze the chemical composition of the two DOM components.In this paper,three sets of marine DOM large-volume extraction equipment based on resin method,SPE method and RO/ED method were successfully constructed.6.3 g DOM samples were extracted by processing 6312 L seawater in batches.The amount and purity of samples can meet the requirements of characterization methods.At the same time,detailed macroscopic properties and molecular composition analysis reveal the selective retention of DOM by different separation methods.