Online Counter Gradient LC-FT-ICR-MS Enables Detection of Highly Polar Natural Organic Matter Fractions

Abstract

Natural organic matter (NOM) is a highly complex mixture of natural organic molecules. The recent developments in NOM molecular characterization methods have shown that ESI-FT-ICR hyphenated with liquid chromatography (LC) is a promising approach to also obtain chemical information (such as polarity and molecular size) about NOM molecules. However, due to changing solvent composition during gradient elution in LC-FT-ICR-MS, ionization conditions also change throughout the chromatographic separation process. In this study, we applied a post-LC column counter gradient (CG) to ensure stable solvent conditions for transient ESI-MS signals. Suwanee River Fulvic Acid (SRFA) standard and a peat pore water were used as representative dissolved NOM samples for method development and validation. Our results show that in polar NOM fractions (which elute with <50% methanol) the TIC intensity and number of assigned molecular formulas were increased by 48% and 20%, as compared to the standard gradient (SG) method. Further application of a Q-isolation and selective ion accumulation for low abundance fractions revealed over 3 times more molecular formulas (especially for CHNO, CHOS, CHNOS formula classes) than in full scan mode. The number of detected highly polar NOM compounds (with elemental ratios H/C < 1, O/C > 0.6) were more than 20 times larger for CG-LC mode as compared to direct infusion (DI) (5715 vs 266 MF). We conclude that the application of a postcolumn counter gradient in LC-FT-ICR-MS analyses of NOM offers novel insight into the most polar fractions of NOM which are inaccessible in conventional DI measurements.

Delineating Source Contributions to Stream Dissolved Organic Matter Composition Under Baseflow Conditions in Forested Headwater Catchments

“…The RI also allow the comparison of peak intensities across samples, with an increase in RI indicating an enrichment of the respective compounds contributing to the overall DOM. Throughout the manuscript, we refer to an assigned DOM molecular formula as compound, although a DOM molecular formula potentially represents multiple isomers (Han et al., 2021).…”

Probing the impact of a phytoplankton bloom on the chemistry of nascent sea spray aerosol using high-resolution mass spectrometry

“…Analysis of DOM by coupling of mass spectrometry with liquid chromatography has been performed with Orbitrap [57,58] and more recently also with FT-ICR-MS [e.g. 59,60].…”

Identification of Unknown Substances in Ambient Air (PM10), Profiles and Differences between Rural, Urban and Industrial Areas

“…In the literature, there are few studies related to non-target analysis in ambient air using liquid chromatographic techniques coupled to high-resolution mass spectrometry [ 34 , 35 , 36 , 37 , 38 ], but in some cases, only MS 2 fragmentation data were employed. The other published studies in the literature employed gas chromatography [ 39 , 40 , 41 ].…”