Study On Analysis Method Of Dissolved Organic Matter In Groundwater

Dissolved Organic Matter（DOM）exists widely in groundwater,and its compositions are complex,which is affected by the biogeochemical environment of groundwater and human pollution.At present,total dissolved organic matter is generally detected,but the molecular compositon is unable to characterize.The analysis of DOM is of great significance to the ecological environment and human health.However,there hasn’t had a perfect analytical method yet for the molecular composition and content of DOM in groundwater.In this paper,an analytical method of DOM in groundwater was established using solid phase extraction and ultrahigh performance liquid chromatography combined with quadrupole-Orbitrap high resolution mass spectrometry（UPLC-Q OrbitrapHRMS）technology.Furthermore,the molecular composition characteristics of DOM in typical regional groundwater were studied.The main conclusion are as follows:1.An ultrahigh performance liquid chromatography combined with quadrupole-Orbitrap high resolution mass spectrometry（UPLC-Q OrbitrapHRMS）method was established for the analysis of DOM in groundwater.Phenomenex Kinete×（?） Polar C18（150 × 2.1 mm,2.6 μm）column was used for gradient elution using 0.15% formic acid-0.02% ammonia buffer solution（pH=2.72）and acetonitrile as mobile phases.High resolution mass spectrometry（HRMS）was performed by using an electrospray ionization（ESI）source and a full scan mode.Furthermore,DOM formula assignment program was developed based on high resolution molecular mass detection results,and the molecular fingerprint of DOM was drawn.The overall analysis time was 30 mins.The method showed good reproducibility,with the intra-day Bray-Curtis dissimilarity between 17.98% and 33.04%,and the inter-day Bray-Curtis dissimilarity between19.72% and 39.08%.2.A pretreatment analytical method of DOM in groundwater was established and optimized.The solid phase extraction method was used for groundwater sample prepareation by automatic solid phase extraction instrument and PPL solid phase extraction column.The method showed good reproducability and recovery effect.The intra-day Bray-Curtis dissimilarity was 23.68%～35.58%,the inter-day Bray-Curtis dissimilarity was 15.93%～38.78%,and the Bray-Curtis dissimilarity of simulation samples before and after recovery was23.24%～38.48%.3.The molecular composition of DOM in 12 groundwater samples from 6 towns in Greater Khingan Mountains area,Hei Longjiang Province were analyzed,the molecular fingerprints of DOM were poltted,and the molecular composition characteristics of DOM in different wells were statistically analyzed.The DOM in groundwater in Greater Khingan Mountains area is mainly composed of O-contained and S-contained heteroatomic compounds,and lignin and protein organic matters occupy a large proportion.The number of molecular formula and the accumulative response intensity of DOM in different wells were significantly different,while the distribution differences of heteroatomic types and organic matter types were relatively small.Among them,the DOM molecular composition characteristics in Hongwei Town have high outliers,and the proportion of S-contained heteratomic compounds and protein organic matter is higher than that in other water source.