8-Hydroxyquinoline, selective extraction

Extraction techniques that involve a chemical reaction can be classified as nonselective extraction or concentration, when more than one analyte is extracted from the solution by using the organic collectors (e.g., 8-hydroxyquinoline and dithizone derivatives) and selective extraction or separation. The first step in such an extraction technique is the formation of the complex by adding the reagent(s) to the solution of analyte, and after the extraction of the complex in an organic solvent. The problem that can arise in a SIA system with these types of extraction is the precipitate that is formed, and this can contaminate the other sample and also can block the tubing. To avoid these problems, it is necessary either to dilute the sample in such a way that the precipitation equihbria will not be reached and that all the complex will remain dissolved in the solution, or by derivatization of the hgands to... 

Polymers containing 8-hydroxyquinoline appear to be selective adsorbents for tungsten in alkaline brines (95). In the presence of tartrate and citrate, quinaldic acid [93-10-7] allows the separation of zinc from gallium and indium (96). Either of these compounds can selectively separate lead and zinc from oxide ores as complexes (97). It is also possible to separate by extraction micro quantities of rhenium(VII), using quinoline in basic solution (98). The... 

Ke and Regier [71] have described a direct potentiometric determination of fluoride in seawater after extraction with 8-hydroxyquinoline. This procedure was applied to samples of seawater, fluoridated tap-water, well-water, and effluent from a phosphate reduction plant. Interfering metals, e.g., calcium, magnesium, iron, and aluminium were removed by extraction into a solution of 8-hydroxyquinoline in 2-butoxyethanol-chloroform after addition of glycine-sodium hydroxide buffer solution (pH 10.5 to 10.8). A buffer solution (sodium nitrate-l,2-diamino-cyclohexane-N,N,N. AT-tetra-acetic acid-acetic acid pH 5.5) was then added to adjust the total ionic strength and the fluoride ions were determined by means of a solid membrane fluoride-selective electrode (Orion, model 94-09). Results were in close agreement with and more reproducible than those obtained after distillation [72]. Omission of the extraction led to lower results. Four determinations can be made in one hour. 

The handling and disposal problems associated with the use of liquid solvent extractors have resulted in increased attention to the separation and preconcentration of organic compounds in water by collection in synthetic polymers followed by elution with an organic solvent (2). For example, selective collection and concentration of organic bases on methylacrylic ester resin from dilute water samples have been reported (3). Such collection techniques are especially well-suited to flow-injection measurement techniques. In this study, ionizable organic analytes such as salicylic acid and 8-hydroxyquinoline (oxine) were extracted into a polymer and then back extracted by an aqueous solution. Amperometric measurement using a flow-injection technique was employed to monitor the process. 

Selectivity. Several additional analytes were examined. Extraction efficiencies from 1 mM solutions for a 2-min extraction time were as follows glucose, 2 salicylic acid, 34 oxine, 75 phenol, 22 and p-cresol, 79. 8-Hydroxyquinoline and p-cresol are significantly more extractable than salicylic acid. 8-Hydroxyquinoline can be back extracted either by basic solution (pH >12) or acidic solution (pH <3) because of its amphiprotic behavior (pKi = 5.0 pK2 = 9.90). This experiment was performed by using either 0.1 M NaOH or 0.01 M HC1 with essentially the same results. The extraction step should be performed at pH 7-10. 

Hydroxyquinoline is a group reagent often applied to the precipitation or extraction of a large number of metals. The selectivity of metal reactions with oxine may be enhanced by masking agents such as EDTA, tartrate, oxalate, or cyanide. 

The extraction method using 8-hydroxyquinoline is not very sensitive, but it is highly selective. The really sensitive methods for spectrophotometric determination of aluminium are based on ternary systems, including triphenylmethane reagents (mainly Chrome Azurol S and Eriochrome Cyanine R) and some surfactants. 

Hydroxyquinoline has been used as a basis for low sensitivity extractive-spectrophotometric methods for magnesium [42,43]. The Mg oxinate is extracted into chloroform in the presence of 2-butoxyethanol [42], butylamine [8,42], or Zephiramine. The molar absorptivity with butylamine is 7.0 10 at 388 nm. A more selective method for determination of Mg, using CMAB-oxine — a derivative of 8-hydroxyquinoline — has been recommended [44]. 

Selectivity of solvent extraction may be improved by using masking agents such as fluoride or cyanide ions in connection with 8-hydroxyquinoline. 8-Hydroxyquinoline reagent solution is prepared in an organic solvent (chloroform, butanol, ethylacetate, MIBK). 

The reagent (e.g, diphenylthiocarbazone, diethyldithiocarbamic acid (2-thenoxy)-3,3.3-tri-fluoroacetone, 8-hydroxyquinoline) must be stable to decomposition, even at very low concentrations in acid and neutral media, and must form an extractable chelate with a sufficiently high value of K (for further useful ligands see [38], [40], [58], [83]). Optimum conditions for substoichiometric extraction are calculated from K, /Cha- and ha-Selectivity of the separation can be improved by use of additional masking reagents [54], [57],... 

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