E. Michael Perdue

Proton-binding study of standard and reference fulvic acids, humic acids, and natural organic matter

The acid–base properties of 14 standard and reference materials from the International Humic Substances Society (IHSS) were investigated by potentiometric titration. Titrations were conducted in 0.1 M NaCl under a nitrogen atmosphere, averaging 30 min from start to finish. Concentrations of carboxyl groups and phenolic groups were estimated directly from titration curves. Titration data were also fit to a modified Henderson-Hasselbalch model for two classes of proton-binding sites to obtain “best fit” parameters that describe proton-binding curves for the samples. The model was chosen for its simplicity, its ease of implementation in computer spreadsheets, and its excellent ability to describe the shapes of the titration curves. The carboxyl contents of the IHSS samples are in the general order: terrestrial fulvic acids > aquatic fulvic acids > Suwannee River natural organic matter (NOM) > aquatic humic acids > terrestrial humic acids. Overall, fulvic acids and humic acids have similar phenolic contents; however, all of the aquatically derived samples have higher phenolic contents than the terrestrially derived samples. The acid–base properties of reference Suwannee River NOM are surprisingly similar to those of standard Suwannee River humic acid. Results from titrations in this study were compared with other published results from both direct and indirect titrations. Typically, carboxyl contents for the IHSS samples were in agreement with the results from both methods of titration. Phenolic contents for the IHSS samples were comparable to those determined by direct titrations, but were significantly less than estimates of phenolic content that were based on indirect titrations with Ba(OH)2 and Ca(OAc)2. The average phenolic-to-carboxylic ratio of the IHSS samples is approximately 1:4. Models that assume a 1:2 ratio of phenolic-to-carboxylic groups may overestimate the relative contribution of phenolic groups to the acid–base chemistry of humic substances.

Isolation of dissolved organic matter from the suwannee river using reverse osmosis

Abstract A portable reverse osmosis (RO) system was constructed and used to concentrate dissolved organic matter (DOM) from the Suwannee River in southeastern Georgia. Using this RO system, 150–180 1/h of river water could be processed with 90% recovery of DOM. After further cation exchange and lyophilization of the concentrated river water samples, large quantities of low-ash freeze-dried products were isolated. We highly recommend this RO method for concentration of DOM in fresh waters because (1) a very high percentage of DOM is recovered, which indicates minimal fractionation of the original sample; and (2) the process is quite rapid, which permits large quantities of DOM to be concentrated in a reasonable length of time.

Low molecular weight species in humic and fulvic fractions

Fourier transform solution /sup 1/H nuclear magnetic resonance (NMR) spectrometry with homogated water peak irradiation is a useful method for detecting low molecular weight substances in humic extracts. Succinate, acetate, methanol, formate, lactate and some aryl methoxyl compounds have been detected in extracts from a wide range of sources. In view of the controversy over whether low molecular weight substances are contaminants in humic extracts introduced by the concentration procedure, the authors report that some of these materials are not contaminants since /sup 1/H-NMR can be used to follow their formation from higher molecular weight species.

Natural Organic Matter

Scientists and engineers specialized in geochemistry, chemistry, biology, and ecology of natural waters have collectively contributed thousands of published works dealing with natural organic matter (NOM). That body of scientific information is dispersed across a wide range of disciplinary journals and books, and it ranges in quality from the mundane to the exceptional. This review includes quantitative estimates of the global riverine transport of NOM from the continents to the oceans and the corresponding average concentration of total organic carbon in rivers, methods of isolation and characterization of NOM from inland waters, and simple statistical summaries of the most commonly reported chemical properties of NOM. The chemical properties of NOM are compared and contrasted with those of the major components of biomass to highlight the most distinctive traits of NOM – its high degree of oxidation, its high level of unsaturation, and its high concentration of carboxylic acid functional groups. An integrated analysis of the major chemical properties of NOM, based on the mean and median results of the statistical summaries, is used to demonstrate consistency (or the lack thereof) among reported properties of NOM.

Correcting errors in the thermodynamic database for the equilibrium speciation model MINTEQA2

The thermodynamic database distributed with the widely used equilibrium speciation model MINTEQA2 contains errors in reactions involving organic ligands. Users of this model should check the log equilibrium constants (log K) supplied with the models database against constants from critically reviewed compilations. The comparison of constants is not straightforward and may involve one or more data reduction steps, such as correcting the log K to zero ionic strength and to a temperature of 25°C. More importantly, it is necessary to reformulate the reaction from the literature in terms of the same components (reactants) used in MINTEQA2 before making the comparison. Use of the MINTEQA2 model without correcting errors in the database can lead to significantly erroneous results as is shown here for copper-EDTA speciation.

Impacts of diverted freshwater on dissolved organic matter and microbial communities in Barataria Bay, Louisiana, U.S.A.

Here we present results of an initial assessment of the impacts of a water diversion event on the concentrations and chemical composition of dissolved organic matter (DOM) and bacterioplankton community composition in Barataria Bay, Louisiana U.S.A, an important estuary within the Mississippi River Delta complex. Concentrations and spectral properties of DOM, as reflected by UV/visible absorbance and fluorescence, were strikingly similar at 26 sites sampled along transects near two western and two eastern areas of Barataria Bay in July and September 2010. In September 2010, dissolved organic carbon (DOC) was significantly higher (568.1-1043 μM C, x=755.6+/-117.7 μM C, n=14) than in July 2010 (249.1-577.1 μM C, x=383.7+/-98.31 μM C, n=14); conversely, Abs254 was consistently higher at every site in July (0.105-0.314) than in September (0.080-0.221), averaging 0.24±0.06 in July and 0.15±0.04 in September. Fluorescence data via the fluorescence index (FI450/500) revealed that only 30% (8 of 26) of the July samples had an FI450/500 above 1.36, compared to 96% (25 of 26) for the September samples. This indicates a more terrestrial origin for the July DOM. Bacterioplankton from eastern sites differed in composition from bacterioplankon in western sites in July. These differences appeared to result from reduced salinities caused by the freshwater diversion. Bacterioplankton communities in September differed from those in July, but no spatial structure was observed. Thus, the trends in bacterioplankton and DOM were likely due to changes in water masses (e.g., input of Mississippi River water in July and a return to estuarine waters in September). Discharge of water from the Davis Pond Freshwater Diversion (DPFD) through Barataria Bay may have partially mitigated some adverse effects of the oil spill, inasmuch as DOM is concerned.

Advanced Solid-State NMR Characterization of Marine Dissolved Organic Matter Isolated Using the Coupled Reverse Osmosis/Electrodialysis Method

Advanced (13)C solid-state techniques were employed to investigate the major structural characteristics of two surface-seawater dissolved organic matter (DOM) samples isolated using the novel coupled reverse osmosis/electrodialysis method. The NMR techniques included quantitative (13)C direct polarization/magic angle spinning (DP/MAS) and DP/MAS with recoupled dipolar dephasing, (13)C cross-polarization/total sideband suppression (CP/TOSS), (13)C chemical shift anisotropy filter, CH, CH(2), and CH(n) selection, two-dimensional (1)H-(13)C heteronuclear correlation NMR (2D HETCOR), 2D HETCOR combined with dipolar dephasing, and (15)N cross-polarization/magic angle spinning (CP/MAS). The two samples (Coastal and Marine DOM) were collected at the mouth of the Ogeechee River and in the Gulf Stream, respectively. The NMR results indicated that they were structurally distinct. Coastal DOM contained significantly more aromatic and carbonyl carbons whereas Marine DOM was markedly enriched in alkoxy carbon (e.g., carbohydrate-like moieties). Both samples contained significant amide N, but Coastal DOM had nitrogen bonded to aromatic carbons. Our dipolar-dephased spectra indicated that a large fraction of alkoxy carbons were not protonated. For Coastal DOM, our NMR results were consistent with the presence of the major structural units of (1) carbohydrate-like moieties, (2) lignin residues, (3) peptides or amino sugars, and (4) COO-bonded alkyls. For Marine DOM, they were (1) carbohydrate-like moieties, (2) peptides or amino sugars, and (3) COO-bonded alkyls. In addition, both samples contained significant amounts of nonpolar alkyl groups. The potential sources of the major structural units of DOM were discussed in detail. Nonprotonated O-alkyl carbon content was proposed as a possible index of humification.

A mechanistic study of the high-temperature oxidation of organic matter in a carbon analyzer

Abstract This study examines the mechanism of oxidation of dissolved organic matter (DOM) in a high-temperature combustion (HTC) carbon analyzer. The HTC analyzer, which is commonly used to measure the concentration of dissolved organic carbon (DOC) in seawater, is still largely empirical in its operation, and little information is yet available on the chemical and physical mechanisms responsible for oxidation of DOM. To examine the role of water, which has been hypothesized to be a source of reactive oxidants in HTC analyzers, several experiments were conducted using gaseous hexane samples and several wet/dry carrier gases. Because the quantity of O 2 (g) needed to oxidize an injected sample of DOM is quite small, a substantial effort has been made to exclude O 2 (g) from the combustion furnace of the HTC instrument. In this modified, “air-tight” instrument, the efficiency of conversion of hexane into CO 2 was greatest in dry O 2 and slightly lower in moist O 2 . Hexane was only slightly oxidized in dry N 2 , but it was largely converted into CO 2 when moist N 2 was used as the carrier gas. These experiments confirm that water provides reactive oxidizing species (perhaps hydroxyl radical) that rapidly convert hexane into CO 2 in the combustion tube of a carbon analyzer. Additional experiments with aqueous solutions of potassium hydrogen phthalate and a variety of carrier gases support this basic hypothesis.

Fast Graphically Inspired Algorithm for Assignment of Molecular Formulae in Ultrahigh Resolution Mass Spectrometry

This study focuses on the deterministic task of assigning molecular formulae to exact masses that are generated by ultrahigh resolution mass spectrometry. A new algorithm based on low-mass moieties (LMMs) such as CH4O(-1) and C4O(-3) completely replaces conventional computational loops that explore a user-defined range of C, H, and O when searching for molecular formulae that have a given exact mass. The LMM-based algorithm has been coupled with a combinatorial algorithm that uses nested loops for N, P, S, and (13)C to assign molecular formulae. The resulting program is more than 1700 times faster than its brute-force counterpart that uses nested loops for all elements, and both programs yield identical output files. The new LMM-based program is 1050 times faster than the open-source program HR2, 60 times faster than Molecular Formula Calculator, and 3.6 times faster than MassCalc/FormCalc.