Natural organic matter and humic substances (HS) in soils and sediments participate in numerous biogeochemical processes. Sorption to redox-inert aluminum oxide (Al2O3) was recently found to affect the redox properties of HS both in sorbed and dissolved state. With this study, we aim to decipher the molecular basis for these observations by applying Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS) and mediated electrochemical analysis to Elliott soil, Pahokee peat, and Suwannee river humic acid (HA) samples before and after sorption to polar Al2O3 and a nonpolar sorbent (DAX-8 resin). The FT-ICRMS data provided evidence of preferential sorption of specific HA fractions, primarily tannin-like compounds, to Al2O3. These oxygen-rich compounds bear a high density of redox-active functional groups, and their adsorption leads to a depletion of electron exchange capacity in dissolved HAs and enrichment of HAs adsorbed at Al2O3. Sorption of HAs to DAX-8 was less selective and caused only slight changes in electron exchange capacities of dissolved and sorbed HA fractions. By combining FT-ICRMS and electrochemical approaches, our findings suggest that a selective sorption of oxygen-rich compounds in HA fractions to mineral oxides is a decisive factor for the different redox properties of dissolved and sorbed HA fractions.

中文翻译：

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单宁在氧化铝上的优先吸附会影响腐殖酸级分溶解和吸附后的电子交换能力。

土壤和沉积物中的天然有机物和腐殖质（HS）参与了许多生物地球化学过程。最近发现，对氧化还原惰性氧化铝（Al2O3）的吸附会影响HS在吸附和溶解状态下的氧化还原性能。通过这项研究，我们旨在通过对之前和之后对Elliott土壤，Pahokee泥炭和Suwannee河腐殖酸（HA）样品进行傅里叶变换离子回旋共振质谱（FT-ICRMS）以及介导的电化学分析，来破译这些观测结果的分子基础。吸附到极性Al2O3和非极性吸附剂（DAX-8树脂）之后。FT-ICRMS数据提供了特定HA组分（主要是单宁样化合物）优先吸附到Al2O3的证据。这些富含氧的化合物具有高密度的氧化还原活性官能团，它们的吸附导致溶解的HA中电子交换能力的耗尽，并吸附在Al2O3上的HA富集。HAs对DAX-8的吸附选择性较低，并且仅导致溶解和吸附的HA馏分的电子交换容量发生轻微变化。通过结合FT-ICRMS和电化学方法，我们的发现表明HA馏分中富氧化合物对矿物氧化物的选择性吸附是溶解和吸附的HA馏分的不同氧化还原特性的决定性因素。