Infrared spectroscopy humic substance analysis

In order to investigate the properties of individual fractions of humic substances, various modes of high performance liquid chromatography (HPLC) have been employed. Hydrophobic interaction chromatography (5) has proved to be an effective separation technique, resulting in five distinct humic fractions from one sample. Structural analysis of these fractions was subsequently performed by infrared and nuclear magnetic resonance spectroscopy, and molecular weight distribution was also measured. 

Insofar as humin is an insoluble macromolecular residue, it has mostly been examined by techniques amenable to solid materials (i.e., elemental analysis, infrared, solid-state NMR, and ESR spectroscopy). Degradative techniques such as oxidation, reduction, and pyrolysis have also been employed. All these methods have been used for the study of humic substances and excellent reviews of the various methods are provided by Schnitzer and Khan (1972, 1978) as well as by Stevenson (1982). 

In common with the other humic substances, many of the properties of HA are due to the nature of its functional groups. These include carboxyl, aliphatic and aromatic hydroxyl, carbonyl and amide groups which can be readily detected by infrared spectroscopy. The results obtained by chemical methods of functional group analysis are often difficult to interpret and may be contradictory. This in part is due to the presence of similar functional groups in the non-humic components ("impurities ) which are extracted along with the humic substances. 

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