Solid-phase extraction (SPE) is a traditional pretreatment procedure widely used for dissolved organic matter (DOM) desalination and enrichment prior to the Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis, and the extracts are usually acidified to pH = 2 with hydrochloric acid (HCl) before passing through the cartridge. However, little is known about the effects of acidification on the integrity and molecular composition of DOM. Here, the differences in the molecular compositions in acidified and nonacidified DOM samples of soil, seawater and atmospheric aerosol were performed by FT-ICR MS. The results showed that the quantity and intensity of aromatic compounds with high oxygen content (e.g., polyphenols, tannin-like and highly oxygenated organic compounds) were greatly enhanced after acidification, while highly saturated compounds (lipid-like and aliphatic/peptide-like) were absent. The underlying reason is the variation of solubility and hydrolysis of DOM under acidic conditions. Meanwhile, the effect of acidification on the molecular composition of DOM was also dependent on their original environmental media. Based on these results, we suggest that the extracts of soil samples are selectively acidified according to the focus of research, while the extract is acidified for seawater samples and the pH of the extract can be unadjusted for aerosol samples before the SPE procedure. These findings provide a reference for the selection of suitable pretreatment methods for different experimental purposes and for the comprehensive characterization of samples with different properties.

固相萃取 (SPE) 是一种传统的预处理程序，广泛用于傅立叶变换离子回旋共振质谱 (FT-ICR MS) 分析之前的溶解有机物 (DOM) 脱盐和富集，并且提取物通常被酸化至在通过小柱之前，用盐酸 (HCl) 使 pH = 2。然而，关于酸化对 DOM 的完整性和分子组成的影响知之甚少。在这里，土壤、海水和大气气溶胶的酸化和非酸化 DOM 样品中分子组成的差异是通过 FT-ICR MS 进行的。结果表明，酸化后含氧量高的芳香族化合物（如多酚、类单宁和高含氧有机化合物）的数量和强度大大增强，而高度饱和的化合物（脂质样和脂肪族/肽样）不存在。其根本原因在于酸性条件下DOM溶解度和水解度的变化。同时，酸化对DOM分子组成的影响也取决于其原始环境介质。基于这些结果，我们建议根据研究重点对土壤样品的提取物进行选择性酸化，而对海水样品的提取物进行酸化，并且在 SPE 程序之前可以不调整气溶胶样品的提取物的 pH 值。这些发现为不同实验目的选择合适的预处理方法和不同性质样品的综合表征提供了参考。