Comparing the Spectroscopic and Molecular Characteristics of Different Dissolved Organic Matter Fractions Isolated by Hydrophobic and Anionic Exchange Resins Using Fluorescence Spectroscopy and FT-ICR-MS

Abstract

Despite the environmental significance of dissolved organic matter (DOM), characterizing DOM is still challenging due to its structural complexity and heterogeneity. In this study, three different chemical fractions, including hydrophobic acid (HPOA), transphilic acid (TPIA), and hydrophilic neutral and base (HPIN/B) fractions, were separated from bulk aquatic DOM samples, and their spectral features and the chemical composition at the molecular level were compared using both fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The HPIN/B fraction was distinguished from the two acidic fractions (i.e., HPOA and TPIA) by the EEM-PARAFAC, while the TPIA fraction was discriminated by using the molecular parameters derived from the FT-ICR MS analyses. Statistical comparison suggests that the spectral dissimilarity among the three chemical fractions might result from the acido-basic properties of DOM samples, while the differences in molecular composition were more likely to be affected by the hydrophobicity of the DOM fractions. The non-metric multidimensional scaling map further revealed that the HPOA was the most heterogeneous among the three fractions. The number of overlapping formulas among the three chemical fractions constituted only <5% of all identified formulas, and those between two different fractions ranged from 2.0% to 24.1%, implying relatively homogeneous properties of the individual chemical fractions with respect to molecular composition. Although employing chemical fractionation achieved a lowering of the DOM heterogeneity, prevalent signatures of either acido-basic property or the hydrophobic nature of DOM on the characteristics of three chemical isolated fractions were not found for this study.

Molecular-Level Chemical Characterization of Dissolved Organic Matter in the Ice Shelf Systems of King George Island, Antarctica

“…Numerous studies have been conducted in various regions of the hydrosphere on the molecular composition of DOM by HRMS, and different dominant formulae have been identified. For example, unsaturated compounds (70.4 ± 0.6%) were highly dominant in the Mediterranean Sea (Martínez-Pérez et al, 2017), and lipid and lignin were the most abundant in river waters (Sleighter and Hatcher, 2008;Derrien et al, 2017). Particularly, Sleighter and Hatcher (2008) reported a decrease of aromaticity toward offshore from inshore using Fourier-transform ion cyclotron resonance MS.…”

Molecular Size Distribution of Fluorophores in Aquatic Natural Organic Matter: Application of HPSEC with Multi-Wavelength Absorption and Fluorescence Detection Following LPSEC-PAGE Fractionation

“…Coupled with reversed-phase liquid chromatography and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) fluorescence was used for NOM investigations. 8,9 The first coupling allowed to determine the efficiency of marine NOM separation 8 and the second one explored the differences among three different chemical fractions separated from bulk aquatic DOM samples. 9 However, until now, the localization and chemical structure of fluorophores of aquatic NOM still remains unclear.…”

“…8,9 The first coupling allowed to determine the efficiency of marine NOM separation 8 and the second one explored the differences among three different chemical fractions separated from bulk aquatic DOM samples. 9 However, until now, the localization and chemical structure of fluorophores of aquatic NOM still remains unclear. Yet determining the localization of fluorescent species between different molecular size compounds should be very useful for understanding the chemical structure and fluorescence origin of aquatic NOM.…”

“…Fluorescence is one of the main properties of aquatic NOM that allows fast and sensitive analysis of NOM. − This method provides essential information on the chemical structure of aqueous NOM and requires a very small quantity of sample. Coupled with reversed-phase liquid chromatography and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) fluorescence was used for NOM investigations. , The first coupling allowed to determine the efficiency of marine NOM separation and the second one explored the differences among three different chemical fractions separated from bulk aquatic DOM samples . However, until now, the localization and chemical structure of fluorophores of aquatic NOM still remains unclear.…”

“…Conventional low pressure size-exclusion chromatography (LPSEC) − and high-performance size-exclusion liquid chromatography (HPSEC) ,− are often used to characterize aquatic and terrestrial NOM due to their high fractionation efficiency. To improve information provided by SEC, researchers frequently employed several techniques (UV–visible absorption, carbon content, 2D- and 3D-fluorescence, 1 H- and 13 C NMR, FT-ICR-MS, Pyr-GC-MS) hyphenated in a single analytical chromatographic run ,, or conducted offline. ,,,,,,, For the separation of aquatic and terrestrial humic substances (HS) we have developed a combination of preparative LPSEC and analytical polyacrylamide gel electrophoresis (PAGE), called LPSEC-PAGE, which was for the first time applied to aquatic NOM extracted from rivers and lakes of the U.S. and Finland. , Protein-like fluorescence was found in the highest and medium molecular size fractions, while humic-like fluorescence was detected mostly in the low molecular size fraction.…”