High-Field FTICR-MS Data Evaluation of Natural Organic Matter: Are CHON₅S₂ Molecular Class Formulas Assigned to ¹³C Isotopic <i>m</i>/<i>z</i> and in Reality CHO Components?

The analysis of dissolved organic matter (DOM) using high-field Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) poses challenges in molecular formula assignment. The consideration of ¹³C isotopes provides new insights into the consistent elemental formula solutions. Modern software helps to overcome misinterpretation, but false assignments of molecular classes to mass peaks have rarely been elucidated until now. It will be demonstrated that this can be important with formula assignments comprising exactly five nitrogen and two sulfur atoms in DOM data sets: the molecular class CHON₅S₂. The existence of such components in DOM under tripeptide Met–His–Cys formed with the formula C₁₄H₂₃O₄N₅S₂ cannot be excluded; however, components containing 5 N and 2 S should be suspected to not be highly abundant. The true elemental compositions of such unusual “N₅S₂ moieties” were calculated using Suwannee River fulvic acid (SRFA) data from the literature and one data set from acidic pit lake pore water. The replacement of a H₃N₅S₂ moiety with a ¹³C₁¹²C₅O₄ moiety explained more than 95% of the questionable “N₅S₂ moieties”. This finding was proved by calculation of δ¹³C‰ values from relative peak intensities

Variations of DOM Quality in Inflows of a Drinking Water Reservoir: Linking of van Krevelen Diagrams with EEMF Spectra by Rank Correlation

Elevated concentrations of dissolved organic matter (DOM) such as humic substances in raw water pose significant challenges during the processing of the commercial drinking water supplies. This is a relevant issue in Saxony, Central East Germany, and many other regions worldwide, where drinking water is produced from raw waters with noticeable presence of chromophoric DOM (CDOM), which is assumed to originate from forested watersheds in spring regions of the catchment area. For improved comprehension of DOM molecular composition, the seasonal and spatial variations of humic-like fluorescence and elemental formulas in the catchment area of the Muldenberg reservoir were recorded by excitation emission matrix fluorescence (EEMF) and ultrahigh-resolution mass spectrometry (FT-ICR-MS). The Spearman rank correlation was applied to link the EEMF intensities with exact molecular formulas and their corresponding relative mass peak abundances. Thereby, humic-like fluorescence could be allocated to the pool of oxygen-rich and relatively unsaturated components with stoichiometries similar to those of tannic acids, which are suspected to have a comparatively high disinfection byproduct formation potential associated with the chlorination of raw water. Analogous relationships were established for UV absorption at 254 nm (UV₂₅₄) and dissolved organic carbon (DOC) and compared to the EEMF correlation

Variations of DOM Quality in Inflows of a Drinking Water Reservoir: Linking of van Krevelen Diagrams with EEMF Spectra by Rank Correlation

Elevated concentrations of dissolved organic matter (DOM) such as humic substances in raw water pose significant challenges during the processing of the commercial drinking water supplies. This is a relevant issue in Saxony, Central East Germany, and many other regions worldwide, where drinking water is produced from raw waters with noticeable presence of chromophoric DOM (CDOM), which is assumed to originate from forested watersheds in spring regions of the catchment area. For improved comprehension of DOM molecular composition, the seasonal and spatial variations of humic-like fluorescence and elemental formulas in the catchment area of the Muldenberg reservoir were recorded by excitation emission matrix fluorescence (EEMF) and ultrahigh-resolution mass spectrometry (FT-ICR-MS). The Spearman rank correlation was applied to link the EEMF intensities with exact molecular formulas and their corresponding relative mass peak abundances. Thereby, humic-like fluorescence could be allocated to the pool of oxygen-rich and relatively unsaturated components with stoichiometries similar to those of tannic acids, which are suspected to have a comparatively high disinfection byproduct formation potential associated with the chlorination of raw water. Analogous relationships were established for UV absorption at 254 nm (UV₂₅₄) and dissolved organic carbon (DOC) and compared to the EEMF correlation