Fractionation dissolved organic matter isolation

Once a sample of dissolved organic matter has been isolated, it is still seldom in a form that permits simple analysis. In most cases, there are far too many compounds present and some form of fractionation must take place to remove interferences and simplify analytical procedures. 

R.A. Kerr and J.G. Quinn, Chemical studies on the dissolved organic matter in seawater isolation and fractionation, Deep-Sea Res. 22 (1975) 107-116. 

Ma, H., Allen, H., and Yin, Y. (2001). Characterization of isolated fractions of dissolved organic matter from natural waters and a wastewater effluent. Water Res. 35, 985-996. 

Although original water samples can apply for some techniques, the isolation procedure is essential for better HS characterization with most analytical techniques. The traditional HS isolation method probably is XAD adsorption, which has been widely used for decades in the HS isolation from waters, soils, and organisms. This method can not only isolate HS, but also further separate HS into two fractions (humic acid and fulvic acid). Detailed isolation procedures have been reviewed in previous articles.XAD resins are styrene-divinylbenzene or methyl methacrylate polymer with various hydrophobicities and cross linkages. The resins adsorb dissolved organic matter mainly by hydrophobic binding or weak interactions such as Van Der Waals force, but the exact mechanism of adsorption is still unknown. 

The MinteqA2 database contains dissolved organic matter (DOM) as a component (number 145). The DOM was isolated from the Suwannee River by Serki2 and Perdue (1990) by reverse osmosis. It was not fractionated into humic and fulvic fractions and is thus not identical to the IHSS Suwannee River FA and HA used in this study. 

Beiin C., Quellec C., Lamotte M., Ewald M., Simon Ph. (1993), Characterization by fluorescence of the dissolved organic matter in natural water. Application to fractions obtained by tangential nltrafiltration andXAD resin isolation. Environmental Technology, 14,1131-1144. 

Leenheer J.A. (1996), Fractionation, isolation and characterisation of hydrophilic constituents of dissolved organic matter in water. Natural Organic Matter Workshop, Poitiers, France, September 96, 4. 

Humic substances can be isolated from waters by using column adsorption techniques and concentrated by methods such as vacuum distillation, lyophilization, freezing concentration, ultraflltration, reverse osmosis. The IHSS has adopted the XAD-8 resin adsorption method to isolate humic and fulvic acids from natural waters. In this method, after filtration through a 0.45 pm silver or polymer membrane Alter, the dissolved organic matter (DOM) is fractionated initially into hydrophobic and hydrophilic fractions through preferential adsorption of the hydrophobic fraction on the XAD-8 resin (water sample preacidifled at pH 2... 

Figure 7.6. Differing effects of ionic strength measured as conductivity for (A) DOM collected from Alkali Lake, North Dakota and (B) hydrophilic and hydrophobic acids isolated from soils sampled in the west coast of Sicily. (Adapted from Provenzano et al. Spectroscopic investigation on hydro-phobic and hydrophilic fractions of dissolved organic matter extracted from soils at different salinity. Clean 36(9), 748-753, 2008. Used with permission of John Wiley Sons.) DOM fluorescence of the Int peak increases fivefold as conductivity increased from 8.5 to 20 mS cm h By contrast, both hydrophilic and hydrophobic acid isolates of DOM from salinized soils showed dramatic reductions in fluorescence in similar regions of fluorescence.

Hydrophilic acids represent about 30% of NOM and are sometimes called " hydrophilic HSs This part of NOM is the least characterised and is more difficult to isolate and purify. Volatile fatty acids or sugar acids could be part of this component (Thurman (1983)). To study the impact of these hydrophilic HSs on water treatment processes, both complete NOM samples and fractions such as HS need to be considered. It is therefore important not to concentrate on HSs only, but also compare to NOM. Organic matter also occurs in natural waters as dissolved molecules, as suspended sediments in the form of coated particles and on coated bottom sediments (Thurman (1983)). This colloid-organic interaction will be addressed specifically in a later section (2.9). 

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