水溶有机质难萃取组分组成分析

Composition characterization of difficult-to-extract components of dissolved organic matter

为表征水溶有机质(dissolved organic matter,DOM)在传统固相萃取(solid phase extraction,SPE)中难萃取组分的分子组成,采用轻度催化加氢的方法对一河流支流水样的原水、SPE洗脱液和萃余液DOM进行加氢脱氧反应,在保留分子主体碳骨架不发生破坏的前提下降低化合物极性。应用气相色谱质谱联用(gas chromatography-mass spectrometry,GC-MS)和负离子电喷雾电离源(electrospray ionization,ESI)结合静电场轨道离子阱质谱(Orbitrap mass spectrometry,Orbitrap MS)分析产物分子结构和组成。结果表明,SPE难萃取组分的分子组成与洗脱液相比具有明显差异。SPE洗脱液主要富集中等极性化合物,而残留在萃取柱上未被有效洗脱的主要是游离态正构烷烃和烷基环己烷、烷基苯等非极性和弱极性化合物,SPE萃余液组分主要包括结合态酯类和包含氮杂环、多环芳香族碳骨架的强极性化合物。

For the purpose of characterizing the molecular composition of the difficult-to-extract components of dissolved organic matter(DOM)in traditional solid phase extraction(SPE),a mild catalytic hydrogenation method was employed to reduce the polarity of DOM in raw water,SPE eluate and raffinate of a river tributary while preserving the main carbon skeleton of molecules.The molecular composition and structure of hydrogenation products were analyzed using gas chromatography-mass spectrometry(GC-MS)and negative-ion electrospray ionization(ESI)coupled with Orbitrap mass spectrometry(Orbitrap MS).The results indicate that the difficult-to-extract components exhibit significant differences in structure and composition compared to the SPE eluate.The SPE eluate mainly consists of moderately polar compounds,while the weakly polar compounds such as free n-alkanes,alkylcyclohexanes,and alkylbenzenes have not been effectively eluted by the elution solvent on the SPE cartridge.The raffinate component that is not extracted from SPE mainly contains bound esters and strongly polar compounds with nitrogen-containing heterocyclic and polycyclic aromatic skeletons.