Separation techniques humics

The development of methods of analysis of tria2ines and thek hydroxy metabohtes in humic soil samples with combined chromatographic and ms techniques has been described (78). A two-way approach was used for separating interfering humic substances and for performing stmctural elucidation of the herbicide traces. Humic samples were extracted by supercritical fluid extraction and analy2ed by both hplc/particle beam ms and a new ms/ms method. The new ms /ms unit was of the tandem sector field-time-of-flight/ms type. 

Because of polydisperse nature of HS, the importance of separation methods increased as the science evolved. Various separation methods were widely used for conventional fractionation and characterization of components based on differences in component solubility, charge, molecular weight, and/or size, polarity, hydropho-bicity, and so on (Janos, 2003). More recent research focused on advanced molecular-level analyses of humic mixtures (Hertkorn and Schmitt-Kopplin, 2007), in which a combination of separation techniques, mostly, chromatography, or capillary electrophoresis) were coupled with high-resolution instrumental analysis [e.g., mass spectrometry (MS) or nuclear magnetic resonance (NMR) spectroscopy]. Several examples appeared in the literature, including those that used size exclusion chro-... 

Another technique widely used for size separation of humic materials is field-flow fractionation (FFF) (e.g., Baalousha et al., 2006 Boehme and Wells, 2006 Geckeis et al., 2003 Hassil ov et al., 2007 Siripinyanond et al., 2005 Suteerapataranon et al., 2006 Zanardi-Lamardo et al., 2002). This technique was developed and introduced in 1966 by Giddings (1966) as a method for the separation and characterization of materials ranging in size from macromolecules to particulates. Similar to SEC, FFF... 

The reviewed results showed that online coupling of separation techniques to multiple analytical detectors can provide the most powerful tools for exploring multidimensional chemical space of NOM and HS. The huge potential of applying this approach to unfolding molecular complexity of natural materials is best of all demonstrated by the results of offline characterization of the fractionated humic materials which are discussed below. 

Given considerations show that further studies on compositional space of humic system are needed to reveal the mechanisms controlling humic system evolution. The role of advanced separation technique and high-resolution analytics in disclosing this mystery of nature will be critical. 

Rottmann and Heumann [81] used this separation technique to examine interactions of humic substances with Co and Mo in water. After interaction, three Mo species and two Cu species were identified and the total species concentration corresponded with the total elemental levels. 

Hollow-fiber ultrafiltration can be a very usefiil tool in obtaining size-fractionated samples for chemical and physical analyses of humic and fulvic acids in surface and groundwaters. The technique is very reproducible because it is strictly a physical separation, it minimizes the potential artifacts associated with the more classical chemical separation techniques. The separation method assumes a spherical structure for the cutoffs and therefore is an empirical approach. Nevertheless, hollow fibers can be used much as 0.45 im filters are used to separate particulate versus dissolved material with a great deal of success. 

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. 

Techniques used to separate humic substances from either a dissolved or sedimentary matrix rely on their acid-base solubility properties. In some of the separation techniques, it is likely that some nonhumic material accompanies the humic substances during the purification processes—to an extent... 

Most concentration and isolation techniques, except for evaporative and freeze-concentration techniques, are also the first steps in chemicfd and physical fractionation of aquatic humic substances. This chapter will concentrate primarily on techniques used to subfractionate and chromatographi-cally separate aquatic humic substances previously isolated as crude fractions. 

A number of studies have been made on the occurrence of N in the various humic substances and the distribution between them. In many studies soil organic matter is separated into humic (HA) and fulvic (FA) acids by the traditional technique of alkaline extraction followed by acidification. 

This technique is based on the same separation mechanisms as found in liquid chromatography (LC). In LC, the solubility and the functional group interaction of sample, sorbent, and solvent are optimized to effect separation. In SPE, these interactions are optimized to effect retention or elution. Polar stationary phases, such as silica gel, Florisil and alumina, retain compounds with polar functional group (e.g., phenols, humic acids, and amines). A nonpolar organic solvent (e.g. hexane, dichloromethane) is used to remove nonpolar inferences where the target analyte is a polar compound. Conversely, the same nonpolar solvent may be used to elute a nonpolar analyte, leaving polar inferences adsorbed on the column. 

A method [62] has been described for the determination of down to 2.5pg kg-1 alkylmercury compounds and inorganic mercury in river sediments. This method uses steam distillation to separate methylmercury in the distillate and inorganic mercury in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet digestion with nitric acid and potassium permanganate [63]. The well known adsorptive properties of clays for alkylmercury compounds does not cause a problem in the above method. The presence of humic acid in the sediment did not depress the recovery of alkylmercury compounds by more than 20%. In the presence of metallic sulphides in the sediment sample the recovery of alkylmercury compounds decreased when more than lmg of sulphur was present in the distillate. The addition of 4M hydrochloric acid, instead of 2M hydrochloric acid before distillation completely, eliminated this effect giving a recovery of 90-100%. 

Environmental applications of FIFFF have been carefully collected in a review by Gimbert et al. [35]. Separations of nanoparticles belong to the FIFFF tradition and this sector has recently found new, fully deserved impulse for microparticle separations. The FIFFF technique has been applied to analyze humic material and submicron Fe colloids. Coupled with ICP-MS, FIFFF has been applied to detect the major and trace element chemistry of aquatic colloids in groundwaters and to determine the trace element distribution in soil and compost-derived humic and colloidal fractions in municipal wastewater. Recently, the ICP-AES has also been proposed as a specific detector for FIFFF to analyze inorganic nanoparticles (Figure 12.12). 

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