Operational definitions dissolved matter

Various separation methods have been used to isolate, fractionate, and characterize humic materials. Originally it was fractionation, based on solubility differences of humic components in diluted alkalis and acids, which laid the ground work for the first classifications of humic substances (HS) in the 19th century (Mulder, 1861 Sprengel, 1837) and provided for operational definition of HS (Kononova, 1966). And now, alkali extraction is the method of choice for isolating HS from solid humus-containing substrates like soil, peat, coal, and so on (Swift, 1996), while hydrophobic resins (e.g., Amberlite XAD resins) are typically used to extract HS dissolved in natural waters (Aiken, 1985). Initial research on HS began with the used simple separation methods to prove, examine, and define characteristics of components of humic matter (Oden, 1919).Today, however, advances in HS research require ever more sophisticated techniques of separation combined with structural analysis (Orlov, 1990 Stevenson, 1994). 

The following are operation definitions of various types of particulate organic matter (POM) and dissolved organic matter (DOM) ... 

Humin s insolubility obviates its presence in a dissolved organic matter aquatic sample. In aquatic systems, the operational definitions of humic and fulvic acids are stated somewhat differently [4]. Humic acid and fulvic acid are defined by the aqueous solution pH necessary to desorb them from XAD-8 resin fulvic acid can be desorbed with water humic acid is desorbed with an alkaline aqueous solution. However, the defining operational characteristic, solubility in an aqueous solution as a function of pH, is consistent in both operations. Thus, the use of the term fulvic acid in this paper refers to the humic substance fraction soluble in aqueous solution at any pH value, and the term humic acid refers to the humic substance fraction soluble in alkaline aqueous solution but insoluble under acidic conditions. 

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