Selective extraction experiments

Selective extraction experiments were then performed to see transference of some transition elements (Cu ", Ni ", Co ", and Fe " ) from the aqueous phase to the organic phase by the synthesized polymeric calixarenes. Phase-transfer studies in water-chloroform confirmed that polymer 2b and 3b were Fe ion-selective as was its monomer (1). Extraction of Fe " cation with 2b and 3b was observed to be maximum at pH 5.4. Only trace amounts of other metal cations such as Cu, Ni ", and Co " were transferred from the aqueous to the organic phase (Table 3). Furthermore, the extracted quantities of these cations remained unaffected with increasing pH. The effect of pH on the extraction of 3b was lower and 56% extraction was accomplished even at pH 2.2. The extraction experiments were also performed with calix[4]arene (1) the ratio was 8.4% at pH 2.2. The polymeric calix[4]arenes were selective to extract Fe " from an aqueous solution, which contained Cu +, Ni, Co ", and Fe " cations, and it was observed that the... 

For the selective extraction experiments, surface coatings were collected in a freshwater lake (Cayuga Lake, New York) on glass slides and Pb and Cd adsorption was measured under controlled conditions before and after extractions to determine by difference the adsorptive properties of the extracted component(s). 0.01 M... 

Laboratory experiments, transport modeling, field data, and engineering cost analysis provide complementary information to be used in an assessment of the viability of an MNA approach for a site. Information from kinetic sorption/ desorption experiments, selective extraction experiments, reactive transport modeling, and historical case analyses of plumes at several UMTRA sites can be used to establish a framework for evaluation of MNA for uranium contamination (Brady et al, 1998, 2002 Bryan and Siegel, 1998 Jove-Colon et al, 2001). The results of a recent project conducted at the Hanford 100-N site provided information for evaluation of MNA for a °Sr plume that has reached the Columbia River (Kelley et al, 2002). The study included strontium sorption-desorption studies, strontium transport and hydrologic modeling of the near-river system, and evaluation of the comparative costs and predicted effectiveness of alternative remediation strategies. 

In Pedersen s early experiments, the relative binding of cations by crown ethers was assessed by extraction of alkali metal picrates into an organic phase. In these experiments, the crown ether served to draw into the organic phase a colored molecule which was ordinarily insoluble in this medium. An extension and elaboration of this notion has been developed by Dix and Vdgtle and Nakamura, Takagi, and Ueno In efforts by both of these groups, crown ether molecules were appended to chromophoric or colored residues. Ion-selective extraction and interaction with the crown and/or chromophore could produce changes in the absorption spectrum. Examples of molecules so constructed are illustrated below as 7 7 and 18 from refs. 32 and 131, respectively. 

Between pH values of ca. 6 and 12 aqueous solutions hold very little dissolved beryllium because of the low solubility of Be(OH)2. When the pH is raised above 12, the hydroxide begins to dissolve with the formation of, first, Be(OH)3 and then, at even higher pH values, Be(OH) (52). The presence of these species in strongly alkaline solutions was confirmed by means of solvent extraction experiments (90) and infrared spectroscopy (31). A speciation diagram is shown in Fig. 7, which was constructed using the values of log /33 = 18.8 and log /34 = 18.6 critically selected from Table III. The diagram illustrates clearly the precipitation and dissolution of Be(OH)2. 

The cation selectivity in extraction experiments is dependent on differences in both the distribution constants KD and the binding constants Klf) in the water-saturated organic solvent (3). The extractability of alkali cations into... 

The individual lines of the doublet signals relax with different rates due to the phenomenon of cross-correlated dipole-CSA relaxation. The CCR-rate can be extracted from the ratio of the intensity of the peaks /dipoie-csA = l/2tln (fhighfieldAowfieid)> where t is the time the selected coherences experience relaxation, and I denotes the signal intensities of the spin states. 

Propylene carbonate is a good solvent of the rhodium precursor [Rh(acac) (00)2] and the phosphite ligand BIPHEPHOS and can thus be used as the catalyst phase in the investigation of the isomerizing hydroformylation of trans-4-octene to n-nonanal in a biphasic system [24]. As already mentioned, the reaction products can be extracted with the hydrocarbon dodecane. Instead of an additional extraction after the catalytic reaction, we carried out in-situ extraction experiments, where the products are separated from the catalytic propylene carbonate phase while the reaction is still in progress. Conversion of 96% and selectivity of 72% was achieved under comparably mild conditions (p(CO/H2) = 10 bar, T = 125 °C, 4 h, substrate/Rh = 200 1). 

Receptor models 71a and 71b for dinucleotides (dinucleoside monophosphates) have been developed out of 69 by replacing the naphthoyl residue, which is not involved in any host-guest interactions in the complexes, by a second carbazolyl cleft. The adenine selectivity of the two pincers was reflected in single extraction experiments dissolved in CH2CI2,71a removes one full equivalent of both adenylyl(3 -+ 5 )adenosine (ApA) and 2 -deoxyadenylyl(3 ->5 )-2 -deoxyadenosine [d(ApA)] 72 out of aqueous solutions of guest (8-fold excess) but only half the amount of d(ApG) [103]. 

Conditions of recovery of the polymer from the latex must be controlled strictly to avoid modifying the copolymer structure (mainly crosslinking and consequent gel formation by oxidation). A partially soluble polymer can be studied by selective extraction, but experience shows that extraction conditions favor crosslinking and/or degradation. Thus results obtained by extraction must be accepted very cautiously. 

In the course of Ln(III) extraction experiments, a new extraction mechanism was discovered the uptake of two different metal cations by calix[4]arene CAc5 in the cone conformation. This positive allostericity renders the calix[4]arene more selective in mutual Ln(III) extraction than the analogous calix[6]arene CAcl at a similar level of extraction power.202-203 A similar effect was observed for Am3+ in the extraction by CAc5 (+Na+) and by CAc8 (+K+).204... 

In considering the differential or selective binding of one anion or another, the intrinsic properties of anions mean that we are not on a level playing field it is considerably easier to bind some anions than others. In general, in the absence of specific chemical recognition between anion and host, anion binding selectivity, particularly in solvent extraction experiments or in the detection of anions by membrane-based ion selective electrodes, follows the order of anion hydrophobicity. This order is termed the Hofmeister series, or lyotropic series and was first outlined in 1888 from experiments based on the... 

Competitive (seven-metal) solvent extraction experiments (water/chloroform) and related bulk membrane transport (water/chloroform/water) experiments have been performed in which each of the four tri-branched ligands as well as their single ring analogues were employed as the extractant/ionophore in the respective chloroform phases [37], In both sets of experiments the aqueous source phases contained an equimolar mixture of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ag(I) and Pb(II) nitrates and were buffered at pH 4.9. For membrane transport the aqueous receiving phase was buffered at pH 3 under these conditions any transport will be driven by the back transfer of protons. Under the conditions employed, the results from the solvent extraction and the bulk membrane transport experiments clearly paralleled each other -for each ligand system high extraction/transport selectivity for Ag(I) was observed over the other six metal ions present in the respective source phases. 

The residual activity in the cells after the dynamic experiment was selectively extracted using techniques previously described. The extracted activity, expressed as a percentage of starting inventory, is compared in Table VI to inventories predicted by the DFO model, which was fitted to tracer concentrations in the groundwater. Also shown in Table VI are the static... 

Selective Chemical Extraction, minerals, the interpretation of selective extraction data requires knowledge of the sorptive capacity of those minerals and their susceptibility to alteration during the course of experiments ... 

Correlation of total surface inventories, obtained by selective extraction of the mixing-cell, to thg degree granite alteration and to temperature, indicates that Co and DSe show a positive correlation with both alteration and temperature. Cobalt-60 and Se inventories for the experiments conducted with fresh granite at 20°C and at 60°C (Reference No. 37 and 34, Table III) indicate about a factor of two increase at 60 C, as would be expected from the production of oxyhydroxides baggd on th alter-ation rate data. Other residual inventories for Co and Se (Table III) follow a pattern consistent with increased oxyhydr-oxide inventories due to both alteration and elevated temperature. 

In the coupon experiment, 60 to 75% of the sorbed Ce was found to be associated with oxyhydroxides and "fixed" by lattice substitution (Figure 4). However, selective extraction data from the mixing-cell tests is ambiguous with respect to the relative importance of exchangeable inventory and that potentially associated with oxyhydroxides. Total surface inventories show a decreasing trend with increasing alteration. No clear trend with temperature is evident. 

Model Fitting to Mixing-Cell Data Multiple-site kinetic models have been used to describe pesticide and herbicide movement in soils (15,16,17), cesium migration in columns (18), and strontium migration in a sandy aquifer over a twenty-year time period (1L). The results of the selective extraction procedures in all experiments discussed here suggest that a multi-site model should provide a better fit of the data than a single-site model. This hypothesis is supported by the variances in Table I, with the possible exception of selenium. 

Although selenium is observed in the geologic setting in association with iron, and the DFO model provides a good fit to the groundwater solution data from the dynamic experiments, the selective extraction inventories do not agree well with the model predictions, and the chemistry of selenium is complicated by redox effects (11) It is likely that the DFO model is still too simple to adequately describe selenium migration ... 

Sequential extraction experiments have been shown to provide a convenient means to determine the metals associated with the principal accumulative phases in sedimentary deposits, to elucidate the mechanisms of their diagenetic transformation, and to elucidate release processes upon changing environmental conditions (Kersten and Forstner, 1989). A general goal of all studies involving selective chemical extraction is the accurate determination of partitioning of elements of environmental concern among different discrete phases of a sample. 

Extraction experiments were performed to evaluate the antioxidant capacity of selected energy crops. Table 1 presents the total phenolics con-... 

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