Identification of next-generation International Humic Substances Society reference materials for advancing the understanding of the role of natural organic matter in the Anthropocene

Abstract

Many challenges remain before we can fully understand the multifaceted role that natural organic matter (NOM) plays in soil and aquatic systems. These challenges remain despite the considerable progress that has been made in understanding NOM’s properties and reactivity using the latest analytical techniques. For nearly 4 decades, the International Humic Substances Society (IHSS, which is a non-profit scientific society) has distributed standard substances that adhere to strict isolation protocols and reference materials that are collected in bulk and originate from clearly defined sites. These NOM standard and reference samples offer relatively uniform materials for designing experiments and developing new analytical methods. The protocols for isolating NOM, and humic and fulvic acid fractions of NOM utilize well-established preparative scale column chromatography and reverse osmosis methods. These standard and reference NOM samples are used by the international scientific community to study NOM across a range of disciplines from engineered to natural systems, thereby seeding the transfer of knowledge across research fields. Recently, powerful new analytical techniques used to characterize NOM have revealed complexities in its composition that transcend the “microbial” vs. “terrestrial” precursor paradigm. To continue to advance NOM research in the Anthropocene epoch, a workshop was convened to identify potential new sites for NOM samples that would encompass a range of sources and precursor materials and would be relevant for studying NOM’s role in mediating environmental and biogeochemical processes. We anticipate that expanding the portfolio of IHSS reference and standard NOM samples available to the research community will enable this diverse group of scientists and engineers to better understand the role that NOM plays globally under the influence of anthropogenic mediated changes.

Characterization of a Newly Available Coastal Marine Dissolved Organic Matter Reference Material (TRM-0522)

“…Nuclear Magnetic Resonance. NMR spectra were acquired at 298 K on a Bruker 500 MHz spectrometer using a TXO CRPHe TR- 13 C/ 15 N/ 1 H 5 mm-Z CryoProbe. The samples were dissolved in D 2 O and referenced to the residual solvent peak at 4.79 ppm in the 1 H NMR spectrum or to MeOH at 49.50 ppm which was added as an external reference for the 13 C NMR spectrum.…”

“…This also corresponds well to our finding of very low SUVA 254 (1.52 L −1 g cm −1 ). In the 13 C NMR spectrum (Figure 4), seven separate regions are presented, according to definitions used in previous reports. 52 −56 Region A covers 0−45 ppm and contains signals corresponding to alkyl chains that are not functionalized with heteroatoms.…”

“…In agreement with the 1 H NMR spectrum analysis, a strong band corresponding to the alcoholic carbons in sugar compounds (95−75 ppm) is observed. While the anomeric signals are obscured by the residual water peak in the 1 H NMR spectrum, a peak attributable to the anomeric carbons of carbohydrates is observed in the 13 C NMR spectrum (∼105− 95 ppm). The remaining two regions contain strong aliphatic signals, with the signal reducing in intensity outside the 55−15 ppm range, consistent with the presence of cyclic and linear terpenoid-derived material, with cyclic material tending toward the higher chemical shift range, and linear material tending toward the lower chemical shift range.…”

“…500 transients were collected and averaged, and a wash solution of 50% methanol: water (LCMS grade) was infused between samples until the blank signal stabilized. Formulas were assigned allowing 4−50 C, 4−100 H, 2−40 O, 0−2 N, 0−1 S, and 0−1 13 C. Combinations of N, S, and 13 C were not allowed nor were double-bond equivalence minus O greater than 10. A 5th order polynomial calibration was performed using a series of expected ions, as given in a previous paper, 25 and formulas were assigned if the mass offset was less than 1.5 ppm.…”

“…1 H NMR spectra were gathered over 330 scans, with a 3.28 s acquisition time and a 15.3 s relaxation delay. 13 C NMR spectra were gathered over 9600 scans, with a 0.92 s acquisition time and an 8 s relaxation delay.…”