Comparison of Sample Preparation Techniques for the (−)ESI-FT-ICR-MS Analysis of Humic and Fulvic Acids

Abstract

Soil organic matter (SOM) plays a key role in the global carbon and nitrogen cycles. Soil biogeochemistry is regularly studied by extracting the base-soluble fractions of SOM: acid-insoluble humic acid (HA) and acid-soluble fulvic acid (FA). Electrospray ionization–Fourier transform–ion cyclotron resonance–mass spectrometry (ESI-FT-ICR-MS) is commonly utilized for molecularly characterizing these fractions. Different sample preparation techniques exist for the analysis of HA and FA though questions remain regarding data comparability following different preparations. Comparisons of different sample preparation techniques here revealed that the negative-mode ESI-FT-ICR-MS analytical window can be skewed to detect different groups of molecules, with primary differences in oxygenation, aromaticity, and molecular weight. It was also observed that HA and FA from soils versus an aquatic matrix behaved very differently. Thus, we conclude that sample preparation techniques determined to be “most optimal” in our study are in no way universal. We recommend that future studies of HA and FA involve similar comparative studies for determining the most suitable sample preparation technique for their particular type of HA or FA matrices. This will enhance data comparability among different studies and environmental systems and ultimately allow us to better understand the complex composition of environmental matrices.

TEnvR: MATLAB-based toolbox for environmental research

“…Once assigned and rened, formula catalogs are highly comparable to those obtained by other soware products. This entire process of molecular formula assignment using TEnvR was validated in a recent publication 53 by comparing data (from numerous acquisitions) obtained on Suwannee River fulvic acid to the formulas published by Hawkes et al 54 In addition, TEnvR was utilized on data published by Yi et al, 55 and the obtained molecular catalogs were very consistent with those obtained from other soware products such as ICBM-OCEAN. 8 A comprehensive description of these comparisons is provided in the tutorial within the ESI.…”

“…41 The codes also evaluate the spectral magnitude changes of formulas common for the samples of interest, which has been determined to be superior to just presence/absence of unique formulas. 5 The comparison codes output a variety of useful gures 53,62,63 and Excel le reports, allowing custom data analysis of the unique and common pools of formulas.…”

Carbon Fate, Iron Dissolution, and Molecular Characterization of Dissolved Organic Matter in Thawed Yedoma Permafrost under Varying Redox Conditions

“…While procedural blanks covering the entire incubation experiments were not prepared, the mass spectra did not contain any unusual “spike” peaks that could be attributed to contaminants. Thus, any extraneous carbon originating from the experimental methodology (e.g., the polypropylene reaction vessels) would have had negligible contributions and been outcompeted by the much higher loadings of permafrost DOM as previously observed for soil extracts …”

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Effects of burning and photochemical degradation of Macondo surrogate oil on its composition and toxicity

“…Samples were directly injected into an Apollo II ESI source operated in negative mode. The instrument was tuned with a polyethylene glycol standard, 37 and the Suwannee River FA (SRFA) standard from the International Humic Substances Society was used to validate the tune and ensure data reproducibility following the recommendations by Hawkes et al (2020). 38 A representative methanolic eluent diluted ×2 was compared to a water-spiked sample (1 : 1 MeOH : H 2 O) to determine the most optimal analysis conditions.…”