Fractionation ultrafiltration techniques

This simplified calculation is used to illustrate basic computational techniques. It assumes that all of the Fe(OH)3(aq) is a true solute. The quality of this assumption is a matter of debate as at pH 8, Fe(OH)3(aq), tends to form colloids. Thus, laboratory measurements of ferrihydrite solubility yield results highly dependent on the method by which [Fe(lll)]jQ(gj is isolated. Ultrafiltration techniques that exclude colloids from the [Fe(lll)]jQjgj pool produce very low equilibrium solubility concentrations, on the order of 0.01 nM. This is an important issue because a significant fraction of the iron in seawater is likely colloidal, some of which is inorganic and some organic. In oxic... 

Leonard, K.S., Harvey, B.R., Woodhead, R.J., Brooks, T. and McCubbin, D. (1994) Assessment of an ultrafiltration technique for the fractionation of radionuclides associated with humic material./. Radioanal. Nucl. Chem. Articles, 181, 309-320. 

In order to clarify the solution properties of poly(VAd) in more detail, poly(VAd) was fractionated by ultrafiltration techniques. The observed molar extinction coefficient of poly(VAd) apparently decreases with an increase in the average molecular weight (Table 13). This suggests that the possibility of an inter-... 

The word flow implies fluid moving through (or across) a rigid framework or conduit (a container, tube, or packed bed) and not being carried with it as in the case of mechanical transfer. Flow is an integral part of many separation techniques, including chromatography, field-flow fractionation, ultrafiltration, and elutriation. The flow process is not itself selective, but it enables one to multiply by many times the benefits of separations attempted without flow. This point is explained in Chapter 7. 

For this study, humic and fulvic materials obtained from a small glaciated bog were separated into five size fractions by using hollow-fiber ultrafiltration techniques. The major cations associated with these organics are reported as a measure of the natural binding capacity of each size range. The structural characteristics and carboxylate content of each group were studied by CIR spectroscopy the results are compared with those obtained by traditional Fourier transform infrared techniques. To aid in spectral interpretation, results were compared to those for selected model polyelectrolytes and simple acids. 

Using ultrafiltration techniques, several investigators have reported protein-bound and nonprotein-bound fractions of plasma aluminium. Lundin et al. (1978) studied the partition of aluminium in the plasma of 10 normal individuals using ultrafiltration with membranes having a cutoff of 6,000-8,000 daltons. The results obtained showed that the protein binding averaged 59% of total serum aluminium. 

Purification of poloxamers has been extensively investigated due to their use in medical applications, the intention often being to remove potentially toxic components. Supercritical fluid fractionation and liquid fractionation have been used successfully to remove low-molecular weight impurities and antioxidants from poloxamers. Gel filtration, high-performance liquid chromatography (HPLC), and ultrafiltration through membranes are among the other techniques examined [5]. 

Buesseler KO, Bauer JE, Chen RF, Eglinton TI, Gustafsson O, Landing W, Mopper K, Moran SB, Santschi PH, Vernon Clark R, Wells ML (1996) An intercomparison of cross-flow filtration techniques used for sampling marine colloids overview and organic carbon results. Marine Chem 55 1-31 Buffle J, Perret D, Newman M (1992) The use of filtration and ultrafiltration for size fractionation of aquatic particles, colloids, and macromolecules. In Enviroiunental particles. Buffle J, van Leeuwen HP (eds) Lewis Publishers, Boca Raton FL, pl71-230... 

The same advantages are exhibited by LC in comparison with techniques such as fractional crystallisation, liquid extraction, ultrafiltration and adsorption. It has already been pointed out (Section 19.6) that LC now plays a major part in bioseparations, where the technique needs to be integrated into the process train as part of a systems approach. 

There are several other techniques that can be used to perform group fractionation. These include dialysis, ultrafiltration, ultracentrifugation, tangential... 

To aid in the characterization of the DOM pool, marine organic chemists have developed techniques fiar separating compounds into size fractions. Tangential flow ultrafiltration is used to isolate a high-molecular-weight (HMW) fraction from a low-molecular-weight (LMW) fraction. The size cutoff between these is approximately 1 tun, which equates... 

Among the fractionation techniques that have been used to study the speciation of trace element containing species include liquid chromatography, gas chromatography, ultrafiltration, dialysis, protein precipitation, electrophoresis and others. In the following sections the application of the above techniques will be discussed. 

Because NMR spectroscopy is a nuclei-specific technique and has the ability to distinguish between similar compounds, it is an excellent method for identifying similar species in complex matrices. Thus, 31P FT-NMR spectroscopy is ideal for the identification and characterization of the hydrosphere DOP. Even so, NMR spectroscopy is fairly insensitive and requires high sample concentrations. Low DOP concentrations are increased to 31P FT-NMR detection limits by using ultrafiltration and reverse osmosis membranes. Not only is the DOP concentrated, but it is fractionated according to its molecular size. Compared to other concentration and molecular size fractionation techniques for DOP, ultrafiltration and reverse osmosis are relatively rapid and easy. 

Because the chapter is about DOM, detailed information about the role of colloids and the analytical techniques are given elsewhere (e.g., Buffle and Leppard, 1995 Kretzschmar et al., 1999 Frimmel et al., 2007). Different separation techniques, like ultrafiltration, size exclusion chromatography, and flow field-flow fractionation can be coupled with UV-vis absorption and ICP-MS to show the interaction of metals and colloids. Elements like Ni, Cu, Cr, and Co are associated mainly with smaller-size DOM fractions whereas Al, Fe, lanthanides, Sn, and Th are associated with larger-size DOM fractions (Bolea et al., 2006). The laser-induced breakdown detection (LIBD) is a new, sensitive method for the quantification of aquatic colloids of lower-range nanometer size in very low concentration, which cannot be... 

The follow-up section will deal with separation methods based upon (a) molecular size and related to it hydrodynamic volume (size-exclusion chromatography and ultrafiltration), (b) molecular size and related to it molecular diffusivity (field-flow fractionation), and (c) charge/size ratio and related to it molecular polarity (electrophoresis and mass spectrometry). Also reviewed will be hyphenated techniques or those that combine separation by chromatography or electrophoresis with spectral detection. 

Ultrafiltration (UF) is a technique that has been widely used for fractionation of HS on the basis of molecular size differences (Janos, 2003). Its application to quantify size and molecular weight characteristics of aquatic humic materials is reviewed in detail by Burba et al. (1998) and Guo and Santchi (2007). 

Techniques can be classified into two main categories those that detect total metal concentrations and those that detect some operationally defined fraction of the total. Methods which detect total concentrations such as inductively coupled plasma spectrometry, neutron activation analysis, atomic absorption spectrometry and atomic emission spectrometry have no inherent speciation capabilities and must be combined with some other separation technique(s) to allow different species to be detected (approach A in Fig. 8.2). Such separation methods normally fractionate a sample on the basis of size, e.g. filtration/ultrafiltration, gel filtration, or a combination of size and charge, e.g. dialysis, ion exchange and solvent extraction (De Vitre et al., 1987 Badey, 1989b Berggren, 1989 1990 Buffle et al., 1992). In all instances the complexes studied must be relatively inert so that their concentrations are not appreciably modified during the fractionation procedure. 

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