Molecular Characterization Method And Application Of Complex Organic Mixture Based On Orbitrap Mass Spectrometry

Petroleum,aerosol,and various water bodies are collectively referred as complex organic mixtures due to the fact of highly mixed.The carbon element circulates among complex organic mixtures and is closely related to energy,climate and environment.Among them,dissolved organic matter(DOM)is widely present in various water environments such as oceans,lakes and groundwater.Its formation mechanism and environmental effects are not yet clear,which limits the treatment and development.The molecular composition of DOM is complex,so far the resolution obtained by chromatography and other separation methods is very limited.The qualitative information of molecular composition obtained by high-resolution mass spectrometry is also affected by ionization selectivity,and the quantitative information is even more lacking.Combining the separation ability of liquid chromatography and the molecular composition characterization ability of high-resolution mass spectrometry,more dimensional information of organic matter molecular characteristics can be obtained.Of course,it also brings challenges to analytical methods and data analysis.This work develops instrument analysis and data processing methods for DOM molecular composition analysis based on electric field orbital trap mass spectrometry(Orbitrap MS),and combines exclusion chromatography and liquid chromatography techniques to study the molecular morphology of DOM.Mainly includes:Study the technical feasibility of Orbitrap MS to analyze the molecular composition of DOM.The difference of analysis on DOM between Orbitrap MS and state-of-the-art Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)was studied.It was found that the resolution of Orbitrap MS is sufficient to analyze DOM,but the stability of low-intensity signals is poor.The influence of instrument parameter settings of Orbitrap MS components on the DOM analysis results was compared,and it was found that high-condensation compounds have stronger signal at high ionization voltages,while high ion transfer tube temperature could weaken the signal response of high-condensation molecules.Study high-resolution mass spectrometry data processing methods.Based on the machine learning method,a method for molecular formula characterization of highresolution mass spectrometry data is developed.The result suggests that molecular features are highly correlated with the correctness of molecular formula identification.The more heteroatoms,the lower the signal-to-noise ratio of the molecular formula,the easier to falsely identified.This method has good application effect in a batch of DOM extracted from inland water,with an accuracy rate of about 90%.Study the molecular composition and aggregation behavior of DOM.The size exclusion chromatography and Orbitrap MS were online hyphenated.It found that the "macromolecule compound" in size exclusion chromatography could not be detected by Orbitrap MS.Through three-dimensional fluorescence and tandem mass spectrometry,suggests the "macromolecule compound" is aggregation of small molecules and is easily decomposed during ionization.Online coupled with reversed-phase chromatography and Orbitrap MS,a chromatographic-MS data processing algorithm was developed to analyze the relationship between compound type and retention time at a high frame rate.It is found that the retention time of high oxygen molecules has an extension phenomenon,and it is speculated that there are multiple interaction forces in complex organic mixtures in reversed-phase chromatography,which affect the retention time of compounds.