Fraction bound

In this one reaction both PQ and P Q are generated simultaneously. These complexes can be referred to as either the bound fraction of P or P. However in radioassay and radioimmunoassay techniques, the concern is with the bound fraction of P (i.e., P Q), since it is this complex that is measured. 

Four types of techniques for separating the bound fraction P Q from the reagent mixture are in common usage, loosely termed double antibody, solid phase, charcoal adsorption and solution precipitation. The first type is used with radioimmunoassay methods specifically, while the other three types can be used with both radioassay and radioimmunoassay methods. 

Since both of these compounds are very large they cannot enter the pores, thus the pores are still free to hold small molecules. When the coated charcoal is added to the assay reagent mixture, the free (unbound) material is adsorbed while the larger bound fraction is not. Final separation is accomplished by centrifugation and decantation of the supernatant. 

Calcium ion-selective electrodes have recently been commercialized for the measurement of either total or ionized calcium Approximately 45 % of the calcium present in serum is bound to proteins, 5% is complexed to simple anions and 50% exists as the free ion. Traditionally, total calcium measurements have been made by releasing the protein bound fraction. An ion-selective electrode has now allowed the free (ionized) calcium to be measured directly. There has been much debate on the clinical significance of these measurements. The dependence of ionized calcium on pH must be considered. Samples must be either treated anaerobically, tonometered to a constant pH or have a correction factor applied. 

Thorium is a highly insoluble element, mainly carried in the particulate form in river waters. This is well shown by Th data for the MacKenzie river (Vigier et al. 2001) and for the Kalix river (Andersson et al. 1995 Porcelli et al. 2001) in both cases, more than 95% of Th is carried by >0.45 pm particles. An important part of this Th is included within detrital material. This is illustrated by sequential extractions performed on sediments from the Witham river (Plater et al. 1992), which show the very low amount of Th in ion-exchangeable and organic-bound fractions compared to Th in Fe-Mn oxides... 

Ferric ion was immobilized on a Chelating Sepharose Fast Flow column preparatory to the separation of seven enkephalin-related phosphopep-tides.17 Non-phosphorylated peptides flowed through the column, and the bound fraction contained the product. The capacity of the column was found to be 23 pmol/mL by frontal elution analysis. Cupric ion was immobilized on Chelating Superose for the isolation of bovine serum albumin.18 Cupric ion was immobilized on a Pharmacia HiTrap column for the separation of Protein C from prothrombin, a separation that was used to model the subsequent apparently successful separation of Factor IX from prothrombin Factor IX activity of the eluate was, however, not checked.19 Imidazole was used as the displacement agent to recover p-galactosidase from unclarified homogenates injected onto a nickel-loaded IMAC column.20 Pretreatment with nucleases and cleaning in place between injections were required procedures. A sixfold purification factor was observed. 

If this binding does occur, then one would expect very strongly bound compounds to show an unusual affinity for the aqueous phase. This could increase the mobility of these compounds in the environment. It is likely that the bound fraction will undergo phase transfers and degradation at different rates than the free truly dissolved fraction of a dissolved pollutant. If this is the case, then an observed equilibrium between a pollutant in the free and bound states could significantly affect its environmental behavior. 

In a dialysis experiment, a dialysis bag containing the dissolved humic materials is placed in a solution of a pollutant (preferably radiolabeled). The dialysis tubing is chosen so the pollutant is free to diffuse through the bag while the humic materials are retained inside the bag. The solution is shaken at constant temperature until it comes to an equilibrium point. At equilibrium, the pollutant inside the dialysis bag consists of two fractions that truly dissolved and the bound to the humic materials. The concentration of pollutant on the outside of the dialysis bag consists only of the free, truly dissolved fraction. Any increase of the pollutant concentration on the inside of the dialysis bag is due to binding by dissolved humic materials. A series of dialysis experiments, therefore, can measure the bound fraction concentration as a function of the free concentration. 

In a solubility experiment the solubility of the compound of interest is measured in the presence and absence of dissolved humic materials. Two techniques were used to measure solubility a shake and filter method similar to that used by Yalkowsky, and a flow through column technique similar to that used by May et al. 9 The measured solubilities of a number of compounds in our experiments were always higher in the presence of humic materials. This increase in the solubility is due to the binding of the compound by humic materials. In the presence of humic materials the measured solubility consists of two fractions free and bound. The free concentration should be the same in the presence or absence of humic materials. The difference between the solubilities of the compound in the presence and absence of humic materials is therefore a measurement of the bound fraction. 

The cumulative sums of selected major and trace metals extracted by the two SSD procedures from representative arid-zone soils are shown in Fig. 4.6. As can be seen from the figure, the Rehovot procedure is stronger in attacking desired fractions, such as the carbonate bound, Mn oxide bound and organically bound fractions. Extraction of certain major elements, indicating selectivity, specificity and completeness of extraction of given soil components, was found to differ between the two procedures. Calcium and Mg were more completely extracted from the carbonate fraction in arid zone soils by the Rehovot procedure. Calcium and relevant trace elements bound in the carbonate fraction, which were not completely dissolved by the Bonn procedure at this step, were released at the following steps, such as the ERO, OM or RO fractions. 

Figure 5.3. Effects of soil pH on the Zn amount bound to the Fe oxide fraction (amorphous/crystalline Fe oxide and overall Fe oxide bound fractions) in soils from China with pH 3.73-8.1 and 0-14.7% CaC03 (after Han et al., 1995. Reprinted from Geoderma, 66, Han F.X., Hu A.T., Qi H.Y., Transformation and distribution of forms of zinc in acid, neutral and calcareous soils of China, p 128, Copyright (1995), with permission from Elsevier)...

Trace elements can be adsorbed on the surface of calcite, influencing their solubility in calcareous soils of arid and semi-arid zones. The carbonate bound fraction is the major solid-phase component for many trace elements (Cd, Pb, Zn, Ni and Cu) in arid and semi-arid soils, especially in newly contaminated soils (Table 5.3). In Israeli arid soils treated with metal nitrates, the carbonate bound fraction is the largest solid-phase component (60-80%, 50-60%, 40-60%, 30-40%, and 25-36% for Cd, Pb, Zn, Ni, and Cu respectively). Divalent metallic cations at low aqueous concentrations first associate with calcite via adsorption reactions. Then they may be incorporated into the calcite lattice as a co-precipitate by recrystallization (Franklin and Morse, 1983 Komicker et al., 1985 Davis et al., 1987 Zachara et al., 1988 Reeder and Prosky, 1986 Pingitore and... 

Cadmium in native arid soils predominates in the carbonate fraction. In 45 uncontaminated Israeli soils, Cd is mainly present in the carbonate bound fraction (43.5% 22.3%), followed by the easily reducible oxide bound fraction (22% 19.5%) (Table 5.4) (Banin et al., 1997a). The... 

Lead has been found to reside mainly in the carbonate and the residual fractions in arid soils. In Californian soils, most of the Pb is in the carbonate fraction (55%), compared to 20% in the residual fraction (Sposito et al., 1982). In Israeli arid soils, Pb is predominately in the residual and the crystalline Fe oxide bound fractions (Han and Banin, 1999). In the delta of the Guadalquiver River of Southwestern Spain, Pb is primarily present in the Fe-Mn oxide bound fraction, followed by the carbonate fraction, while the organic and the exchangeable fractions are small (Ramos et al., 1994). In uncontaminated arid soils of China, Pb is mainly in the residual fraction, followed by the carbonate and the oxide bound fractions (Jin et al., 1996). 

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