Ion association extraction

In the ion-association extraction systems, hydrophobic and interfacially adsorbable ions are encountered very often. Complexes of Fe(II), Cu(II), and Zn(II) with 1,10-phenanthro-line (phen) and its hydrophobic derivatives exhibited remarkable interfacial adsorptivity, although the ligands themselves can hardly adsorb at the interface, except for protonated species [19-21]. Solvent extraction photometry of Fe(II) with phen is widely used for the determination of trace amounts of Fe(II). The extraction rate profiles of Fe(II) with phen and its dimethyl (DMP) and diphenyl (DPP) derivatives into chloroform are shown in Fig.9. In the presence of 0.1 M NaC104, the interfacial adsorption of phen complex is most remarkable. The adsorption of the extractable complex must be considered in the analysis of the extraction kinetic mechanism of these systems. The observed initial rate r° shows the relation... 

FIG. 9 Extraction rate profiles of the ion-association extraction of Fe(II) with phen and its dimethyl (DMP) and diphenyl (DPP) derivatives into chloroform in the presence of 0.1 M NaC104. Effect of stirring (4700 rpm) indicates the interfacial adsorption of the complexes. 

SCHEME 3 Interfacial mechanism in the ion-association extraction of Fe(II) with phen or its derivatives (L) including an anion X. 

From the fundamental knowledge concerning the interfacial complexation mechanism obtained from the kinetic studies on chelate extraction, ion-association extraction, and synergistic extraction, one can design the interfacial catalysis. The main strategy is to raise the concentration of the reactant or intermediate at the interface. 

TABLE 3 Extraction Parameters in the Ion-Association Extraction of Fe(II) with Phen and Its Derivatives... 

Table 4.4 Typical ion-association extraction systems System...

The so-called "trapped sites" of classical mobile-site, liquid ion exchanger electrodes belong to a category of compounds known as ion association extractants. Examples are long-chain diesters of phosphoric acid and tricaprylylmethylammonium (Aliquat) ions. The latter cation was studied extensively by Freiser and co-workers (1-3 ) in the design of anion sensors. 

The analysis of brines perhaps deserves special mention as the high sodium chloride concentrations are extremely unfavourable for electrothermal atomisation and most troublesome in flame analysis. The preferred approach is probably solvent extraction with either oxine or APDC to remove the trace metals into a small volume of MIBK for flame atomisation or chloroform for electrothermal cells. Care must be taken to avoid interference from chloro-complexes in the extraction, and if this is suspected an ion-association extraction of these complexes might be preferable. 

Oxygen-containing organic solvents extract the charged forms of the reagent as ion-pairs. Some metals (Ni, Zn, U) form anionic oxine complexes, which form with basic dyes ion-associates, extractable into benzene [109]. 

Mercury(II) forms anionic complexes with F, Br, and CF ions, which react with basic dyes to give ion-associates extractable into organic solvents. Sensitive extractive spectro-photometric methods for determining mercury are based on such reactions with the following dyes Crystal Violet (e = O-IO -IO-IO ) [43 6], Malachite Green and Methyl... 

The methods of determining Te with the use of basic dyes are very sensitive. The tellurium bromide complex has been extracted as the ion-associate with Butylrhodamine B [44,45] or Victoria Blue 4R (e = 8.0-10 ) [46]. The halide complexes give also ion-associates, extractable into toluene (e = 3.75-10 ) with Violet Red [47 9]. The TeBr associate with Rhodamine 6G can be floated with benzene, and the separated compound is then dissolved in a mixture of benzene with ethanol (e = 1.7-10 ) [50]. The ion-associate of the iodide complex of Te(IV) with Nile Blue A has been floated with cyclohexane, and the separated compound dissolved in methanol (e = 1.4-10 at 640 nm) [51]. High sensitivity has... 

Group 1, Ion formation extractant Group 2, Ion association extractant Group 3, Solvating extractant. 

Benzalkonium, cetylpyridinium (quaternary ammonium salts) Pharmaceutical formulations 1,2-dichloroethane UV—Vis 5.0 x 1CU7—2.0 x 10 6 mol L 1 C-FIA membrane for phase separation ion association extraction and thermochromism of the ion associates [453]... 

Similarly, the uranyl ion is extracted from aqueous nitrate solution into isobutanol by associating with two nitrate ions (U02 , 2N03 ), with the uranium probably being solvated by the solvent to make it solventlike. Permanganate forms an ion pair with tetraphenylarsonium ion [(C6H5)4As , Mn04"], which makes it organiclike, and it is extracted into methylene chloride. There are numerous other examples of ion-association extractions. 

As with chelate systems, ion-association extraction equilibria involve a number of reactions. An example is the extraction of Fe " from HCl solutions into ether. 

Substoichiometric separation is performed by ordinary chemical separation methods such as solvent extraction, ion exchange, precipitation, and electrochemical methods. In recent years, however, the ion exchange and electrochemical methods have not been used very much in substoichiometric separation. The precipitation technique is often used due to its simplicity, while solvent extraction is most widely employed. This is because the procedure for solvent extraction is very simple and an appropriate extraction system can usually be selected from the great number of research papers dealing with solvent extraction of many different elements. Two extraction systems are commonly used chelate extraction of metal ions with chelating agents and ion-association extraction of metal ions with simple negative or positive ions. 

H. Frieser, Relevance of Solubility Parameter in Ion Association Extraction Systems, Anal Chem. 41(10), 1354 (1969). 

H. Watarai, Effect of stirring on the ion-association extraction of copper and zinc 4,7-diphenyl-l,10-phenanthroline complexes, Talanta, 32, 817-820 (1985). 

H. Watarai and Y. Shibuya, Interfacial adsorption of iron(II)-4,7-diphenyl-l,10-phen-anthroline complex in ion-association extraction systems. Bull. Chem. Soc. Jpn., 62, 3446-3450 (1989). 

Figure 8 shows this relationship for sorption of Cd(II) and Zn(II). Both plots gave a straight line with a slope of 2, indicating that the reaction depicted in equation 8 indeed took place. Although the n-value was not determined due to difficulty in varying the [RC1]r value in equation 9, the n-value of 1 or 2 may be reasonable in comparison with the ion-association extraction behavior (13). 

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