Fulvic functional groups

Table 1 Range of Di.stribution of Oxygen-Containing Functional Groups in Humic and Fulvic Acids Isolated from Soils of Widely Different Climatic Zones (in mEq/lOO g)...

In spite of this variation in molecular weights and solubilities humic acid and fulvic acid have a very similar chemical composition. These acids consist of aromatic moieties such as phenols, benzenepolycarboxylic acids, hydroxybenzenepolycarbo-xylic acids, 1,2-dihydroxybenzene carboxylic acids, together with more complex condensed structures and polycylic compounds. It is conjectured that these various units are joined together by aliphatic chains (45, 54) the distribution of functional groups is presented in Table 5. 

Functional Group Quantity m equivalents g fulvic acid... 

The concentrations of HS fractions, i. e., fulvic acids, humic acids, and humin expressed as mol Cl kg of SPH s in terms of various functional groups such as carboxyl, phenolic OH, alcoholic OH, and carbonyl are shown in Fig. 10. 

Functional groups constitute about 20-30% of the humic molecules About 25% of soil humic acids and about 50-60% of a fulvic acid molecule consist of functional groups... 

Table 8.19 Oxygen-based functional groups in 1982). Concentrations expressed in mEq/100 g. humic and fulvic acids (from Stevenson, ...

Figure 8.26 (A) Functional groups of humic substances. (B) Complexing schemes for fulvic substances. Reprinted from Stevenson (1983), with kind permission of Theophrastus Publishing and Proprietary Co.

Table 2 Typical Compositions of Oxygen Functional Groups in Fulvic and Humic Acids (mmolg-1)166...

A problem for both humic- and yellow substances is that for these groups of experimentally defined components of different sources, each analysis will be ambiguous in terms of relative composition and molecular weight distribution. Additionally it appears that almost every scientist working in this field has developed his own extraction procedure (Weber and Wilson, 1975 Mantoura and Riley, 1975 a Schnitzer, 1976 Stuermer and Harvey, 1977). Different extraction times and -procedures result in different compositions of the organic constituents (Laane and Kramer, 1984). Soil humic-and fulvic acids, often used for studies on the interaction with trace elements, and those derived from water have certainly not the same composition and contain not the same distribution of functional groups. Therefore, results should be compared with care (Buffle, 1980 Buffle et al., 1984). 

Soil- and sediment-derived fulvic acid is also composed of aromatic, aliphatic, and carbohydrate carbon components, though it is generally believed to be more aromatic than the humic acid from that same environment. A typical fulvic acid s elemental composition is 46.2% C, 4.9% H, 2.5% N, 45.6% O, and 1.2% S (Rice and MacCarthy, 1991). The carboxyl group is the predominant functional group in... 

Ephraim, J. H., Alegret, S., Mathuthu, A., Bicking, M., Malcom, R.L., and Marinsky, J. A. (1986). A unified physicochemical description of the protonationandmetal ion complex-ation equilibria of natural organic acids (humic and fulvic acids). 2. Influence of polyelectrolyte properties and functional group heterogeneity on the protonation equilibria of fulvic acid. Environ. Sci. Technol. 20, 354-366. 

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