Humic materials isolation

Estimates of true MW variations in HS of different genesis can be derived from results reported by Perminova et al. (2003). Here a large suite of humic materials, isolated from different aquatic and terrestrial environments, were analyzed using standardized SEC conditions the same column packing (Toyopearl F1W50S) and mobile phase (0.028 mol liter-1 phosphate buffer at pH 6.8). Figure 13.4 summarizes results. 

Many researchers have attempted to unravel the mystery of the structure of humus. One approach has been to isolate fractions by extracting humus using various extraction procedures. These procedures result in the isolation of three or more fractions humic acid, fulvic acid, and humin. Humic material is isolated from soil by treating it with alkali. The insoluble material remaining after this treatment is called humin. The alkali solution is acidified to a pH of 1.0 and the precipitate is called humic acid, while the soluble... 

Experiments to identify disinfection by-products (DBFs) have been carried out using two different procedures. In the first, natural waters (e.g., river, lake) are reacted with the disinfectant, either in a pilot plant, an actual treatment plant, or in a controlled laboratory smdy. fii the second type of procedure, aquatic humic material is isolated and reacted with the disinfectant in purified water in a controlled laboratory study. This latter type of study is relevant because humic material is an important precursor of THMs and other DBFs. Aquatic humic material is present in nearly all natural waters, and isolated humic material reacts with disinfectants to produce most of the same DBFs found from natural waters. Because DBFs are typically formed at low levels (ng/L-pg/L), samples are usually concentrated to allow for DBF detection. Concentration methods that are commonly used include solid phase extraction (SFE), solid phase microextraction (SFME), liquid-liquid extraction, and XAD resin extraction (for larger quantities of water) [9]. 

An extraction method for isolating humic substances from water by using XAD-8 has been proposed by Thurman and Malcolm (9) (see box). Humic substances in natural waters represent almost the entire hydrophobic acid fraction. This method has been used to isolate 4.25 g of humic substances from 24,500 L of ground water from the Fox-hills-Laramie aquifer and to obtain 500 g of humic material from 10,400 L of the Suwannee River (Table II). The sample from the Suwannee River was collected as a reference sample of aquatic humic substances by the International Humic Substances Society. In both of the examples cited, a fc cutoff of 100 was used. 

Other potential DOP isolation methods are based on sorption using anion-exchange resins or nonionic resins. Extensive research in concentrating humic material has employed these methods (55). For isolation and concentration of DOP, these techniques have several disadvantages, such as possible irreversible sorption onto the resins and the concentration of all anionic species present in the sample. Another major drawback is the need to use a strong base to remove the sorbed material from the resin. For sorption to occur with nonionic resins requires the protonation of all weak acids, thus exposing the sample to low pH. 

Soil polysaccharides can amount to as much as 20% of the humic fractions isolated in aqueous media, and identification of the classes of components in humin materials in associations with the soil clays indicates that carbohydrates contribute significantly to those isolated in the DMS0/H2S04 medium (see Sections 1.4.7 and... 

Figure 4.9. Electron spin resonance spectra of humic acids isolated from unamended soil (a) and soil amended with 90, 225, and 630tha-1 of sewage sludge (b, c, and d, respectively). Reprinted from Senesi, N. (1989). Composted materials as organic fertilizers. Sci. Total Environ. 81/82, 521-542, with permission from Elsevier.

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 photodegradation of an aqueous solution of terbuthylazine was not only accelerated, but was also more extensive in the presence of humic acids isolated from soil (Mansour et al., 1997). In the absence of humic acids, only hydroxyterbuthylazine (OBET) was formed (Sanlaville et al., 1996), whereas in the presence of humic acids, dealkylated products (CBAT, CBDT, CEAT, CAAT, OAAT) were formed (Table 23.2) (Sanlaville et al., 1996 Mansour et al., 1997). In contrast, fulvic acids isolated from stream water slowed the photolysis of terbuthylazine, most likely reflecting differences in structure between the soil- and stream-derived materials. The photodegradation of atrazine and its initial photoproduct OEIT (Table 23.2) in artificial sea water containing humic acids was also accelerated compared to photolysis in distilled water (Durand et al., 1990,1991). 

Molecular fluorescence has been shown to be a valuable tool for studying the binding of certain metal ions to both isolated humic materials (1-4) and natural organic matter present in samples collected from lakes, rivers and other bodies of water (5,6). Paramagnetic metal ions tend to reduce or quench fluorescence which has been demonstrated for Cu " (1-5), Co " (4,6), Mn " (4), Ni (1), Fe " and Fe " (7) with various samples of humic materials. Diamagnetic metal ions, on the other hand, may quench, show no effect or even enhance humic material fluorescence depending on the metal, the source of the humic material and other experimental factors (1,8-13)... 

Humic substances isolated from stream samples from each site fell within these common ranges, with Como Creek humic substances accounting for 55% of the DOC whereas the Suwannee River humic substances accounted for 81 % of the DOC. In contrast, foam humic substances accounted for 93% of the DOC from Como Creek foam and for 89% of the DOC from the Suwannee River foam. Organic carbon determinations were not made on the foam-extract fraction, and the percentage contribution by weight of humic substances to this material could not be determined. 

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