Application of Sequential Solid Phase Extraction to Dissolved Organic Matter for Unknown Screening Analysis with an Orbitrap Mass Spectrometer

摘要

Isolation of complex dissolved organic matter (DOM) from environmental water is a major challenge for unknown screening analysis with a high resolution mass spectrometer. A technique with high dissolved organic carbon (DOC) recovery is imperative to reveal the composition of DOM. In this study, DOM in river water was fractionated sequentially by three solid phase extraction (SPE) cartridges based on the polarity and charge of DOM molecules. The sequential SPE achieved 80-95% of DOC recovery which was double of DOC recovered by single SPE with functionalized styrene divinylbenzene polymer. Orbitrap mass spectrometry revealed approximately five thousands of molecular formulae for the SPE extracts. Based on the number of assigned formulae, hydrophobic neutral (HPON) fraction was the most abundant followed by hydrophobic acid (HPOA), hydrophilic acid (HPIA) and base (HPIB) fractions. Hydrophobic base (HPOB) and hydrophilic neutral (HPIN) fractions were barely detected in all the samples. Molecules in HPON fraction were the most unsaturated (high (DBE-0)/C) and least oxidized (low carbon oxidation state) among all fractions. Kendrick mass analysis indicated that the HPON molecules had unique long CH_2 chain and low oxygenated characters while those molecules in HPOA and HPIA fractions had shorter CH_2 chain and were more oxygenated.