Abstract
This chapter provides an insight into the humic molecular structure. Humic substances are those materials produced in soils that are either yellow or brown-to-black colored, acidic, polydisperse substances of relatively high molecular weight. Curtain electrophoresis is the most appropriate method for fractionating humic substances. The molecular weights of soil humic substances range from 2,000–3,000 for the alkali-soluble, acid-soluble fractions to well over 300,000 for the fractions insoluble in both alkali and acid. Many kinds of degradative procedures have been applied to humus fractions. These procedures include acid hydrolysis, alkaline hydrolysis, oxidation, reduction, pyrolysis, and thermogravimetry. The chapter discusses several chemical methods of functional group (for e.g., total acidity, carboxyl groups, hydroxyl groups, and carbonyl groups) analysis. The results obtained by chemical methods of functional group analysis are difficult to interpret and often contradictory. Spectrographic methods such as ultraviolet spectroscopy, infrared spectroscopy, and magnetic resonance spectroscopy are among the most useful of the nondestructive methods of examining unknown chemical compounds. Several techniques that may have applications to humic substances in soils are also discussed in the chapter. These techniques include halogenation, acid hydrolysis, hydrogenolysis, spectroscopy, and estimation of aromaticity. Finally, the chapter suggests several hypotheses on structure of humic substances.
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