The anion-exchange extraction of thiocyanate, chloride and iodide cadmium complexes by solutions of quaternary ammonium salts chlorides in organic solvents (toluene, carbon tetrachloride, ethyl acetate, isobutyl alcohol, nitrobenzene) was studied. Extraction involves solutions of alkyl dimethylbenzylammonium chlorides (R-N+(CH3)2-CH2C6H5-Cl-) and alkyl dimethylethyl-benzylammonium (R-N+(CH3)2-CH2-CH2C6H5-Cl-), where R is a straight alkyl chain, mainly C12 - C14. The composition of the cadmium anionic complexes was established by the analysis of the calibration curves E = f (pCCd (II)) constructed from cadmium sulfate solutions against the background of various contents of thiocyanate, chloride and iodide ions (ndicator electrode - ion-selective electrode with a membrane, which based on a nitrobenzene solution of tetradecylammonium bromide). The extraction process is estimated quantitatively using a distribution coefficient (D). The value of D is calculated taking into account the cadmium concentration in the aqueous phase before and after extraction. The dependence of the distribution coefficient on the organic solvent dielectric constant, the concentration and stability of the anionic complexes of cadmium is shown. So, for the indicated cadmium acidocomplexes, the minimum D values were obtained using low-polar toluene and carbon tetrachloride, and the maximum values were obtained using highly polar isobutyl alcohol and nitrobenzene. If the concentration of cadmium (II) is reduced by a factor of 100 for the cadmium rhodanide and iodide complexes, the value of D decreases by 1.6-1.9 times, for the chloride complex, by 1.2 times in the case of polar isobutyl alcohol and nitrobenzene, and 2.9-3.5 times in the case of low-polar solvents. It was experimentally established that in the series [Cd(SCN)4]2- - [CdI4]2-- [CdCl4]2- the value of D decreases for all the studied systems. The observed regularity is related both to the stability of the corresponding cadmium (II) complexes in aqueous solutions and to their hydrophobicity.
The anion-exchange extraction of salicylate, thiosulphate and thiocyanate iron (III) complexes by solutions of chlorides of quaternary ammonium salts (QAS) in organic solvents (toluene, carbon tetrachloride, ethyl acetate, isobutyl alcohol, nitrobenzene) was studied. The composition of the iron (III) anionic complexes was established by the analysis of the calibration curves E = f(pCFe (III)) constructed from iron (III) solutions against the background of various contents of thiocyanate, thiosulphate and salicylate ions and the steepness of the electrode function. As an indicator electrode the ion-selective electrode was used with a membrane, which based on a nitrobenzene solution of tetradecylammonium bromide. The solution containing of alkyldimethylbenzylammonium chloride and alkyldimethylethylbenzylammonium chloride and the corresponding organic solvent were mixed in a ratio of 1:1. An organic layer containing the QAS was selected. The anion-exchange extraction was provided in contact with aqueoses solutions of Fe(III) anionic complexes. The extraction process is estimated quantitatively using a distribution coefficient (D). The value of D is calculated taking into account the iron (III) concentration in the aqueous phase before and after extraction. The content of iron (III) in solutions is determined spectrophotometrically (λ = 440 nm). It is established that the value of the distribution coefficient depends on the permittivity (ε) of the organic solvent. In the row toluene - carbon tetrachloride - ethyl acetate - isobutyl alcohol - nitrobenzene, the permittivity increases. In the same sequence, D increases for all studied complex iron(III) ions. Moreover, a decrease in the concentration of the extracted particle leads to an insignificant decrease in the value of the distribution coefficient. The composition and stability of the complex iron (III) ion have a significant effect on the extraction activity.
The possibility of ionometric determination of zinc in the rhodanide complex form in milk is represented. The indicator electrode was ion-selective electrode (ISE) with solution of tetradecylammonium bromide in nitrobenzene as a membrane. As a complexing agent the potassium thiocyanate with 1.0 mol/l optimal concentration in investigated solutions was selected. The calibration dependence E = f(pCZn(II)) were typical anionic functions. The steepness of the electrode function (29±2 mV/pC), close to the theoretical value for the doubly−charged ions, suggests that the electrochemically active anions are [Zn(NCS)4]2-. The interval of linearity of calibration curves is 1.0 to 5.7 pC, the detection limit is equal to 1∙10-6 mol/l. The selectivity of determination of zinc in the rhodanide complex form was investigated with “The mixed solutions” method in the presence of potassium, calcium, aluminum, iron (III), manganese (II), copper (II) chlorides potassium iodide and nitric acid solutions. The background concentration of extraneous (j) substances in investigated solutions was calculated with usage of published data and corresponds to their maximum content in milk. It was founded that the ionometric determination of zinc is possible in range from 1.0 to 5.0 pC for all investigated j-ions. The technique for different types of milk was developed including preliminary sample preparation, used in special certified laboratories and based on dry mineralization of sample and dissolving in nitric acid solution. The concentrations of zinc-ions in analyzed samples were determined with “limiting solutions” method. The correctness of obtained data was confirmed with “entered-found” scheme. The relative standard deviation was not higher then 0.08.
The ability of iron (III) ionometric determination in a form of its thiosulfate complex was shown. Conditions of analysis were optimized. The obtained anionic electrode function E=f(pCFe(III) obeys to the Nernst equation in the range of 2.0 to 5.0 unit of MS and has a slope equals to 56±2 mV/pC. The determination selectivity in the presence of a number of cations and anions was studied by the “mixed” solutions method. The method was applied for the analysis of iron (III) content in some fruit and vegetables.
The anion-exchange extraction of salicylate, thiosulphate and thiocyanate iron (III) complexes by solutions of quaternary ammonium salts (QAS) chlorides in organic solvents (toluene, carbon tetrachloride, ethyl acetate, isobutyl alcohol, nitrobenzene) was studied. The composition of the iron (III) anionic complexes was established by the analysis of the calibration curves E = f (pCFe (III)) constructed from iron (III) solutions against the background of various contents of thiocyanate, thiosulphate and salicylate ions and the steepness of the electrode function. As an indicator electrode was used the ion-selective electrode with a membrane, which based on a nitrobenzene solution of tetradecylammonium bromide. The solution containing of alkyldimethylbenzylammonium chloride and alkyldimethylethylbenzylammonium chloride and the corresponding organic solvent were mixed in a ratio 1: 1. An organic layer containing the QAS was selected. The anion-exchange extraction was provided in contact with aqueoses solutions of Fe(III) anionic complexes. The extraction process is estimated quantitatively using a distribution coefficient (D), the value of D is calculated taking into account the iron (III) concentration in the aqueous phase before and after extraction. The content of iron (III) in solutions is determined spectrophotometrically (λ = 440 nm). It is established that the value of the distribution coefficient depends on the permittivity (ε) of the organic solvent. In the row toluene - carbon tetrachloride - ethyl acetate - isobutyl alcohol - nitrobenzene, the permittivity increases. In the same sequence, D increases for all studied complex iron(III) ions. Moreover, a decrease in the concentration of the extracted particle leads to an insignificant decrease the value of the distribution coefficient. The composition and stability of the complex iron (III) ion have a significant effect on the extraction activity.
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