Raeke Julia, Lechtenfeld Oliver J, Wagner Martin, Herzsprung Peter, Reemtsma Thorsten
Helmholtz Centre for Environmental Research - UFZ, Department of Analytical Chemistry, Permoserstrasse 15, 04318 Leipzig, Germany.
TZW: DVGW Water Technology Center, Wasserwerkstrasse 2, 01326 Dresden, Germany.
Environ Sci Process Impacts. 2016 Jul 13;18(7):918-27. doi: 10.1039/c6em00200e.
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.
在通过电喷雾电离（ESI）与超高分辨率傅里叶变换离子回旋共振质谱（FT-ICR MS）联用分析溶解有机物（DOM）之前，固相萃取（SPE）常用于富集和净化。一般认为，就碳浓度而言，SPE萃取并非定量的。然而，关于不同SPE吸附剂的选择性以及对所获得的DOM质谱的影响，现有信息较少。使用广泛的PPL、HLB和C18吸附剂对淡水样品进行萃取，并将萃取物和渗透物中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%至65%之间。尺寸排阻色谱与有机碳检测联用（SEC-OCD）表明，PPL和HLB回收率有限主要是由于固相中有一部分表观高分子量物质洗脱不完全。相比之下，主要在C18柱上观察到的固相上的不完全保留归因于一部分低分子量物质。原始样品和SPE萃取物的FT-ICR质谱在分子量分布上没有显著差异，但在氧化程度和饱和度方面显示出吸附剂特异性差异。我们得出结论，SPE对淡水DOM的选择性富集对后续的FT-ICR MS分析不太关键，因为那些未充分回收的部分对质谱的影响相对较小。这通过模型化合物的萃取得到证实，表明极性很强的小分子萃取效果不佳，而且在ESI-MS中的响应也很低。在三种测试的SPE柱中，PPL材料为后续的FT-ICR MS分析提供了最佳的DOM富集性能，因为它将过强和过弱的DOM-吸附剂相互作用降至最低。
