Dissolved organic matter molecular composition data of exemplary marine water masses resolved by online LC-MS@en

The unique chromatographic behaviour of DOM was investigated on three exemplary water samples representing coastal DOM, oceanic surface DOM and oceanic refractory DOM. Weddell Sea surface (30 m depth, oceanic surface DOM) and deep water (1356 m depth, refractory DOM) was sampled with a rosette sampler on RV Polarstern during ANT XXII/2 (station PS67/006-130, latitude -67.5633, longitude -55.3448) and are described elsewhere (El Naggar et al., 2007; Koch et al., 2008). 160 L sea water was filtered with 0.2 µm filter cartridges, acidified to pH 2 and pumped through 60 mL solid phase extraction cartridges (PPL, 5 g). DOM was eluted with 40 mL MeOH and stored at -18 °C. Coastal DOM is routinely extracted from southern North Sea (latitude 54.1447, longitude 7.8711) and used as an in-house laboratory standard. Sea water was filtered over 0.2 µm PTFE (Whatman), acidified to pH 2 and extracted with PPL cartridges. After elution with methanol, extracts are stored at -18 °C until measurement to minimize esterification (Flerus et al., 2011). The molecular composition was obtained by two mass spectrometric platforms with negative electrospray ionisation: 1) Fourier Transform Orbitrap mass spectrometer (FT-Orbitrap-MS; Q-Exactive Plus, Thermo Fisher Scientific, Bremen, Germany) coupled to ultra-high performance liquid chromatography (UPLC, Vanquish, Thermo Fisher Scientific, Bremen, Germany); 2) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS; 7 Tesla scimaX MRMS system, Bruker Daltonics GmbH & Co. KG, Bremen, Germany) coupled to UPLC (Elute LC, Bruker Daltonics GmbH & Co. KG, Bremen, Germany). Reversed phase chromatography was done with a C18 column (Waters AQUITY 2 x 100 mm, 1.7 µm) column at 0.3 mL min 1 and a linear gradient: A (ultrapure water, 4 mmol L 1 ammonium formate) 2 min: 99 %, 11 min: 0 %, 14.9 min: 99 %; B (MeOH, 4 mmol L 1 ammonium formate) 2 min: 1 %, 11 min: 100 %, 14.5 min 100 %, 14.9 min 1 %.本研究针对三类典型水体样品——沿岸溶解性有机质（Dissolved Organic Matter, DOM）、海洋表层溶解性有机质以及海洋难降解溶解性有机质，探究了溶解性有机质独特的色谱行为。威德尔海表层海水（水深30 m，对应海洋表层DOM）与深层海水（水深1356 m，对应难降解DOM）由“极地号”科考船（RV Polarstern）在ANT XXII/2航次（站位PS67/006-130，纬度-67.5633，经度-55.3448）中采用罗塞塔采样器（rosette sampler）采集，相关采样细节已在既往研究中报道（El Naggar等，2007；Koch等，2008）。取160 L海水，使用0.2 μm滤筒过滤，酸化至pH 2后，以泵流方式通过60 mL固相萃取柱（PPL材质，装填量5 g）。溶解性有机质以40 mL甲醇（MeOH）洗脱，随后保存于-18 ℃环境中。沿岸溶解性有机质常规采自北海南部（纬度54.1447，经度7.8711），作为实验室内部标准品使用。海水经0.2 μm聚四氟乙烯（PTFE，Whatman）滤膜过滤后，酸化至pH 2，再通过PPL固相萃取柱完成萃取。以甲醇洗脱后，萃取物保存于-18 ℃直至上机检测，以最大限度抑制酯化反应（Flerus等，2011）。本研究采用两台搭载电喷雾电离负离子模式的质谱平台完成样品分子组成分析：1）傅里叶变换轨道阱质谱（Fourier Transform Orbitrap mass spectrometer, FT-Orbitrap-MS；Q-Exactive Plus，赛默飞世尔科技，德国不来梅），联用超高效液相色谱（Ultra High Performance Liquid Chromatography, UPLC；Vanquish，赛默飞世尔科技，德国不来梅）；2）傅里叶变换离子回旋共振质谱（Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS；7 Tesla scimaX MRMS系统，布鲁克 Daltonics GmbH & Co. KG，德国不来梅），联用超高效液相色谱（UPLC；Elute LC，布鲁克 Daltonics GmbH & Co. KG，德国不来梅）。反相色谱分离采用C18色谱柱（Waters AQUITY 2 × 100 mm，1.7 μm），流速设为0.3 mL·min⁻¹，洗脱梯度如下：流动相A（超纯水，含4 mmol·L⁻¹甲酸铵）：0~2 min为99%，2~11 min线性降至0%，11~14.9 min维持99%；流动相B（甲醇（MeOH），含4 mmol·L⁻¹甲酸铵）：0~2 min为1%，2~11 min线性升至100%，11~14.5 min维持100%，14.5~14.9 min线性降至1%。