Selectivity of solid phase extraction of freshwater dissolved organic matter and its effect on ultrahigh resolution mass spectra
Selectivity of solid phase extraction of freshwater dissolved organic matter and its effect on ultrahigh resolution mass spectra
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DOI：
10.1039/c6em00200e
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发表时间：
2016-01-01
影响因子：
5.5
通讯作者：
Reemtsma, Thorsten
中科院分区：
文献类型：
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作者：
Raeke, Julia;Lechtenfeld, Oliver J.;Reemtsma, Thorsten
固相萃取 (SPE) 通常用于在通过电喷雾电离 (ESI) 结合超高分辨率傅里叶变换离子回旋共振质谱 (FT-ICR MS) 分析溶解有机物 (DOM) 之前进行富集和净化。人们普遍认为，SPE 萃取对于碳浓度而言不是定量的。然而，关于不同 SPE 吸附剂的选择性以及对获得的 DOM 质谱的影响的信息很少。使用广泛使用的 PPL、HLB 和 C18 吸附剂提取淡水样品，并将提取物和渗透物中 DOM 的分子组成和尺寸分布与原始样品进行比较。三种测试的 SPE 吸附剂的溶解有机碳 (DOC) 回收率在 20% 到 65% 之间。尺寸排阻色谱法与有机碳检测 (SEC-OCD) 结合显示，PPL 和 HLB 的回收率有限主要是由于固相中表观高分子量部分的洗脱不完全。相比之下，主要在 C18 柱上观察到的固相不完全保留归因于低分子量部分。原始样品和 SPE 提取物的 FT-ICR 质谱在分子量分布上没有显着差异，但它们在氧合和饱和度方面显示出吸附剂特定的差异。我们得出的结论是，通过 SPE 选择性富集淡水 DOM 对于后续 FT-ICR MS 分析来说不太重要，因为那些未充分回收的馏分对质谱的影响相对较小。模型化合物的提取证实了这一点，表明极极性和小分子的提取效果较差，而且在 ESI-MS 中的响应也较低。在三个测试的 SPE 小柱中，PPL 材料为随后的 FT-ICR MS 分析提供了 DOM 富集的最佳特性，因为它最大限度地减少了过强和过弱的 DOM-吸附剂相互作用。
Solid phase extraction (SPE) is often used for enrichment and clean-up prior to analysis of dissolved organic matter (DOM) by electrospray ionization (ESI) coupled to ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It is generally accepted that extraction by SPE is not quantitative with respect to carbon concentration. However, little information is available on the selectivity of different SPE sorbents and the resulting effect for the acquired DOM mass spectra. Freshwater samples were extracted by the widely used PPL, HLB and C18 sorbents and the molecular composition and size distribution of the DOM in the extracts and in the permeates was compared to the original sample. Dissolved organic carbon (DOC) recoveries ranged between 20% and 65% for the three tested SPE sorbents. Size-exclusion chromatography coupled to organic carbon detection (SEC-OCD) revealed that limited recovery by PPL and HLB was primarily due to incomplete elution of a fraction of apparent high molecular weight from the solid phase. In contrast, incomplete retention on the solid phase, mainly observed for the C18 cartridge, was attributed to a fraction of low molecular weight. The FT-ICR mass spectra of the original sample and the SPE extracts did not differ significantly in their molecular weight distribution, but they showed sorbent specific differences in the degree of oxygenation and saturation. We concluded that the selective enrichment of freshwater DOM by SPE is less critical for subsequent FT-ICR MS analysis, because those fractions that are not sufficiently recovered have comparatively small effects on the mass spectra. This was confirmed by the extraction of model compounds, showing that very polar and small molecules are poorly extracted, but also have a low response in ESI-MS. Of the three tested SPE cartridges the PPL material offered the best properties for DOM enrichment for subsequent FT-ICR MS analysis as it minimizes too strong and too weak DOM-sorbent interactions.