Natural organic matter (NOM) adsorption on nanoparticle (NP) surfaces in natural waters forms a corona that can alter NP properties and its environmental fate. Anthropogenic NPs are usually coated with an organic capping agent that may, in turn, influence the extent and molecular composition of the corona. Up-to-now, the molecular composition of the NOM corona can only be analyzed in controlled experiments due to a lack of appropriate direct surface analysis methods. Here, we introduce laser desorption ionization Fourier-transform ion cyclotron resonance mass spectrometry (LDI-FT-ICR-MS) to directly analyze Suwannee River Fulvic Acid (SRFA) after adsorption and sequential desorption on gold (Au) NPs capped with small molecules (citric acid (CA), tannic acid (TA), lipoic acid (LA)) and large polymers (polyvinylpyrrolidone (PVP), branched polyethylenimine (BPEI), methoxy polyethylene glycol sulfhydryl (m-PEG-SH)). LDI-FT-ICR-MS revealed differences in the molecular composition of the NP corona depending on the capping agents' chemistry. Positively charged BPEI efficiently adsorbed larger oxygen-rich aromatics whereas negatively charged CA and LA adsorbed oxygen-containing aromatics. The weak negative PVP adsorbed oxygen-containing aliphatics and non-charged m-PEG-SH small oxygen-depleted aliphatics, both with lower efficiency. However, TA preferentially adsorbed polyphenolic compounds from SRFA due to its similar chemistry. Further comparison of the Au-CA corona with the conventional indirect electrospray ionization (ESI)-FT-ICR-MS analysis largely confirmed the results of the new direct LDI analysis. Due to the higher sensitivity of the direct method, LDI-FT-ICR-MS can be applied to environmentally relevant NOM : NP ratios which was not possible before. LDI-FT-ICR-MS is a promising method to study the extent and molecular composition of NP coronas and suitable to better elucidate NP fate in the environment.

中文翻译：

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通过激光解吸电离傅里叶变换离子回旋共振质谱法直接分析吸附在封端的金纳米颗粒上的富里酸

天然水中纳米颗粒 (NP) 表面上的天然有机物 (NOM) 吸附形成了一个电晕，可以改变 NP 的特性及其环境命运。人为 NPs 通常涂有有机封端剂，这反过来可能会影响电晕的范围和分子组成。迄今为止，由于缺乏适当的直接表面分析方法，只能在受控实验中分析 NOM 电晕的分子组成。在这里，我们引入了激光解吸电离傅里叶变换离子回旋共振质谱 (LDI-FT-ICR-MS) 来直接分析 Suwannee River Fulvic Acid (SRFA) 在被小分子覆盖的金 (Au) NPs 上吸附和顺序解吸后的情况。柠檬酸 (CA)、单宁酸 (TA)、硫辛酸 (LA)) 和大聚合物（聚乙烯吡咯烷酮 (PVP)、支化聚乙烯亚胺 (BPEI)、甲氧基聚乙二醇巯基 (m-PEG-SH))。LDI-FT-ICR-MS 揭示了 NP 电晕的分子组成的差异，这取决于封端剂的化学性质。带正电的 BPEI 有效吸附较大的富氧芳烃，而带负电的 CA 和 LA 吸附含氧芳烃。弱负性 PVP 吸附含氧脂肪族化合物和不带电荷的 m-PEG-SH 小耗氧脂肪族化合物，两者的效率较低。然而，由于其相似的化学性质，TA 优先吸附 SRFA 中的多酚化合物。Au-CA 电晕与传统的间接电喷雾电离 (ESI)-FT-ICR-MS 分析的进一步比较在很大程度上证实了新的直接 LDI 分析的结果。由于直接法的灵敏度较高，LDI-FT-ICR-MS 可以应用于环境相关的 NOM : NP 比率，这在以前是不可能的。LDI-FT-ICR-MS 是一种研究 NP 电晕范围和分子组成的有前途的方法，适用于更好地阐明环境中的 NP 归宿。