Elucidating Dissolved Organic Sulfur in the Coastal Environment by Improved Online Liquid Chromatography Coupled to FT‐ICR Mass Spectrometry

Dissolved organic sulfur (DOS) is an important component of dissolved organic matter (DOM) and widely exists at the land‐atmosphere interface. However, the characterization of DOS at the molecular level among different environmental samples in coastal regions has not been sufficiently focused. Here, we investigated DOS in aerosol, rainwater, and river water samples in Shanghai using an improved method–online liquid chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry (LC‐FT‐ICR MS). This system is utilized to separate DOS from complicated environmental matrices. The results showed that the average relative abundance of DOS in three different environmental media (aerosol, rainwater, and river water samples) accounted for 16.8%, 21.9% and 13.1%, respectively. The common molecules of the three mediums in coastal Shanghai contain an abundance of aromatic and aliphatic DOS of anthropogenic origin in addition to the natural sources of sea spray. Notably, results from a new structural classification scheme for DOS demonstrate that anthropogenic sulfonates and their derivatives are widely spread, although their molecular diversity in different medium was recorded due to complex environmental conditions and diverse sources. Plain Language Summary Ion suppression of abundant non‐sulfur containing species hinders the detection of dissolved organic sulfur species by direct infusion electrospray ionization mass spectrometry. A newly developed method is proposed to evaluate organic sulfur‐containing compounds at the molecular level using an online liquid chromatography coupled to ultrahigh resolution mass spectrometry, which was applied to aerosol, rainwater, and river water samples in Shanghai. Our study suggests that the novel method allows a detailed investigation of organic sulfur‐containing compounds and provides molecular evidence of the ubiquitous presence of anthropogenic DOS in the ambient environment. Key Points The ubiquity of natural and anthropogenic dissolved organic sulfur was observed at the water‐atmosphere interface Natural dissolved organic sulfur at the coastal water‐atmosphere interface is mainly from sea spray‐based biological sources Online liquid chromatography coupled to FT‐ICR Mass Spectrometry is an ideal system to separate dissolved organic sulfur