DAX-8和XAD-4串联树脂法大体积提取海水溶解有机质及其分子组成分析

采用DAX-8和XAD-4串联树脂技术（DAX-8/XAD-4法）对青岛近海表层海水的溶解有机质（dissolved organic matter，DOM）进行了大体积的提取制备，获得DOM中的疏水酸性组分（hydrophobic acid，HOA）、亲水酸性组分（hydrophilic acid，HIA）、疏水中性组分（hydrophobic neutral，HON）和亲水中性组分（hydrophilic neutral，HIN）共4个组分。从200 L海水中共提取海洋DOM固体样品0.3 g，总有机碳提取效率为48%。应用傅立叶变换离子回旋共振质谱（Fourier transform ion cyclotron resonance mass spectrometry, FT-ICR MS）对得到的4个组分进行分子组成表征。结果表明，酸性组分（HOA和HIA）可鉴别出4000余个分子，具有相对较高的O/C值，其氧化降解程度较高；中性组分鉴别出1000余个分子，其H/C值较高，具有较低的缩合度。含氮类化合物在亲水组分（HIA和HIN）中相对富集。富羧基脂环化合物（carboxylic-rich alicyclic molecules，CRAM）在酸性组分中相对富集。DAX-8/XAD-4树脂串联法能用于含盐高、DOM含量低的海水，适用于分离提取大体积海水样品中不同极性的DOM亚组分，其样品量及较低的灰分能满足分析表征和模拟实验等应用需求。

Large volume marine DOM isolation and fractionation by DAX-8 and XAD-4 resins-in-tandem and their molecular level characterization by FT-ICR MS

Dissolved organic matter (DOM) was separated from a large volume of surface sweater in offshore Qingdao by DAX-8 and XAD-4 resins used in tandem. Four fractions, namely hydrophobic acid (HOA), hydrophilic acid (HIA), hydrophobic neutral (HON), and hydrophilic neutral (HIN) were obtained. A total of 0.3 g of marine DOM was isolated from 200 L seawater with the total dissolved organic carbon (DOC) extraction recovery of 48%. The four DOM fractions were characterized in molecular level by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).More than 4,000 individual molecules were assigned from HOA and HIA fractions, which have relatively greater O/C ratios and greater degrees of oxidative degradation.More than 1,000 individual formulas were assigned from the neutral fractions which have greater H/C ratios and lower degree of condensation. The nitrogen-containing compounds were relatively enriched in hydrophilic fractions (HIA and HIN). The resins-in-tandem method is capable for seawaters with high salinity and low DOM concentration, and can be used to isolated and fractionate DOM fractions with different polarities from a large volume of seawater. The amount and low ash content of samples can meet the requirements of characterization and biological culture experiments.