Marine fulvic acids

TABLE 1. Ash-Free Elemental Composition of a Marine Fulvic Acid and a Soil... 

TABLE 2. Concentrations of Dissolved Organic Carbon (DOC), Marine Humic Acid, and Marine Fulvic Acid in the Gulf of Mexico"... 

The mechanism of formation and class structure of marine humic substances presented here was first proposed by Harvey et al. (1983). Since that time the proposed pathway and structures of marine fulvic acid and marine humic acid have been tested and the predicted chemical and physical behaviors of marine humic substances have been supported in several experiments. 

The equivalent weight and molecular size data indicate that marine humic substances are approximately 900-1200 daltons and are composed of two to four fatty acid chains (Harvey and Boran, 1982b). The key to the pathway (Fig. 1) is in the NMR spectra in that all the marine fulvic acids and marine humic acids had 79-94% methyl and methylene protons and 2-24% protons on oxygenated carbon. The question then posed was What hydrocarbonlike class of compounds, present in all marine environments, is capable of... 

The natural marine fulvic acid and marine humic acid were removed from 10 L of seawater with XAD-2 resin (Harvey et al., 1983). After readjusting the pH to 8.2, 5 mg of one of the particular lipids was added to the column effluent every half hour, with stirring, up to a total of 5 mg/L. The solution was allowed to stir for 1, 2, or 7 days, depending on the starting material. The solution was then acidified to pH 2 and extracted as above with XAD-2. The yield of product was 50-100 mg. 

The isolated substances were similar to marine fulvic acids. Tripalmitin gave no product and in fact never dissolved. The products were pale yellow powders soluble in acid and base but insoluble in ether or methylene chlo-... 

FIGURE 5. Infrared spectra of (A) a natural marine fulvic acid isolated from the Gulf of lexico and (B) a synthetic fulvic prepared by the autoxidation of trilinolein. 

WGURE 9. Proton NMR of a marine fulvic acid showing the high amounts of methyl and methylene protons in the 0.9-2.5 ppm range. Note the small amount of aromatic protons at 7.1 ppm. 

RP-HPLC and online 3DEEM detection were recently combined to study fluorescence properties of HS fractions as a function of polarity.SRFA and Aldrich humic acid (AHA) can be separated by stepwise RP-HPLC into several fractions, a red-shifted fluorescence maximum pattern and an increase in molecular size were found when the fraction changing from hydrophilic to hydrophobic. In a similar smdy, Lombardi and Jardrm separated a soil and marine fulvic acid into several classes of fractions with different fluorophores, which were related to their distinct origins. 

The study of humic substances by nuclear magnetic resonance of the isotope and the proton suggests that aliphatic structures prevail over aromatic structures for the fulvic acids extracted from marine water, contrary to the case for soil fulvic acids. The high values of the H C ratio in marine fulvic acids also point to an aliphatic nature (Stuermer and Payne, 1976). 

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