Fulvic acid class structure

The designation of certain classes of organic materials as humic and fulvic acids unfortunately implies a certainty and regularity of structure which... 

Recall from Chapter 23.2.4 that humic substances are isolated from seawater by adsorption on a hydrophobic resin followed by elution using solvents of varying pH. The desorbed compounds are fractionated into two classes, humic acids fulvic acids based on their solubility behavior. A model structure for a humic acid is illustrated in Figure 23.10a in which fragments of biomolecules, such as sugars, oligosaccharides. 

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 classical definition of fulvic acids is not very specific. Many biochemical substances such as proteins, sugars, and fatty acids would fall under this classification. These substances, in many instances, can hardly be considered "humic" in nature. But, if one uses the classical definition of fulvic acids these substances are included. No doubt the observations made above that polysaccharidelike substances constitute the major components of sedimentary fulvic acids is partly attributable to the fact that the operational definition classes polyuronides as fulvic acids. It is not the intent of this paper to discuss the merits of using the classical operational definition for fulvic acids as opposed to one s perception of what true fulvic acids are. He know far too little about the composition of humic isolates and about their origin to begin discussions of whether they are humified or not. He therefore chose to use operational definition with recognition that well defined structural entities can sometimes be a part of what is isolated. 

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