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Rakhmatov Khudoyor Boboniyozovich, Associate professor of the of the technological machines and equipment faculty of the Karshi Engineering-Economics Institute
Republic of Uzbekistan, Karshi E-mail: [email protected] Djurayeva Shokhista Dilmurodovna, Senior lecturer of the Chemistry Faculty of the Karshi Engineering-Economics Institute, Republic of Uzbekistan, Karshi Ubaydullaeva Ismoilovna Dilfuza, Associate professor of the of the Chemistry Faculty of the Karshi Engineering-Economics Institute, Republic of Uzbekistan, Karshi, Khidirova Zulkhumor Uralovna, Senior lecturer of the Chemistry Faculty of the Karshi Engineering-Economics Institute, Republic of Uzbekistan, Karshi Bobilova Chinnigul Khayitovna, Assistant professor of the Chemistry Faculty of the Karshi Engineering-Economics Institute,
Republic of Uzbekistan, Karshi
AMPEROMETRIC TITRATION OF NOBLE METALS BY ORGANIC REAGENTS SOLUTIONS IN NON-AQUEOUS MEDIA
Abstract: The article describes conditions and possibility of amperometric titration of palladium (II) and platinum (IV), silver (I) and gold (III) ions with solutions of 4-methoxyphenyl-carboxymethyl-diethyldithiocarbamate (MPCMDETC) and 4-methoxyphenyl-carboxymethyl-diphenylthiocarbazone (MPCMDPTC) in non-aqueous media (acetic acid, n-propanol, DMF, DMSO) with background electrolytes having various acid-base properties. Techniques of the amperometric titration of micrograms of the quantities of palladium (II), platinum (IV), silver (I) and gold (III) ions in the presence of foreign ions are shown
Keywords: palladium, platinum, silver, gold, electrooxidation, anodic wave, acetic acid, n-propanol, background electrolytes, equivalence point.
Amperometric titration of metal ions in nonaqueous and mixed media by various complexants makes it possible to expand their analytical capabilities and simplify the solution of many complex analytical problems. First and foremost, this is related to
the fact that the nature of the solvent strongly affects the strength of the complex formed, and it is dissimilar for different cations, which makes the tecnique selective and rapid. Aside from that, the tecnique of non-aqueous compleximetry successfully solve the
problem of precise and selective determination of metals in organic objects, as well as directly in extracts obtained by concentration.
The article presents experimental data on the selection ofoptimal amperometric titration conditions for a number ofnoble metals by solutions of derivatives of organic reagents such as diethyl-dithiocarbamate and diphenylthiocarbazone: 4-methoxyphenyl-carboxy-methyl-diethyldithiocarbamate (MPCMDETC) and (4-methoxyphenyl-carboxymethyl)-diphenylthiocar-bazone (MPCMDPTC) in non-aqueous protolytic media, acid-base properties of background electrolytes. There are no data on the use of both analytical titrants in the amperometric titration of ions of various metals by the solutions of the above reagents, since they were synthesized relatively recently [1] and only their biological activity have been studied [2].
Reagents and apparatus. Base 0.002 M solutions of Na2PdCl4, K2PtCl6, AuCl3 and AgNO3, as well as 0.01 M solutions of MPCMDETC and MP-CMDPTC were blended by dissolving the corresponding weighed portions of these reagents in acetic acid (n-propanol, DMF and DMSO). The noble metal concentration was determined amperimetri-cally by 0.01 M potassium iodide solution [3]. Amperometric titration was carried out on two rotating (1000 rpm) platinum wire electrodes on a common axis configuration. The configuration of electrodes, as well as piston automatic microburette and apparatus are described in detail in [4].
Amperometric titration was carried out on aon two rotating (1000 rpm) platinum wire electrodes on a common axis configuration. The configuration of electrodes, as well as piston automatic microburette and apparatus are described in detail in [5].
In accordance with the voltammetric behavior of MPCMDETC, MPCMDPTC and other products participating in electrochemical media of ampero-metric titration of noble metal ions, it should be carried out at polarization voltage of 0.75-1.15 V depending on the nature and concentration of the background electrolyte (acetates, nitrates, chlorides,
perchlorates of alkali metals and ammonium) [6, 7]. The indicator current must appear behind the point of equivalence (PE) due to the oxidation of the free reagent and the dissolved oxygen recovering.
The data acquired showed that in the media and backgrounds studied of 0.15-0.40 M solutions of noble metal ions with solutions of MPCMDETC and MPCMDPTC are titrated quite well and rapidly, and the shape of the curve coincides with the expected shape with some constant current at the beginning of the titration followed by a sharp transition (kink) at the end point of titration (EPT).
Analysis of noble metal ions in individual solutions. It was found that when the ions of the following noble metals are titrated with the corresponding molar ratio Me: reagent is: Pd: 1:2 reagent and Pt: 1:4 reagent, the titrated solution acquires a reddish-brown color. In the transition from acetate background to perchlorate containing some amount of perchloric acid, the shape of the titration curve of noble metal ions deteriorates significantly, which ultimately leads to a decrease in the reproducibility and correctness of the results. This is due to the increased acidity of the analyzed medium when changing from acetates to perchlorates [8, 9]. The results of the analysis of different concentrations of noble metal ions by MPCMDETC solution of 10.0 ml of the analyzed solution under optimal conditions shows good accuracy of the developed procedure. Influence of additives to acetic acid, n-propanol, DMF, DMSO of frequently used as extragents of inert solvent, such as chloroform, tetrachlorometh-ane, benzene, toluene, hexane, methyl ethyl ketone, dioxane, etc., on correctness and reproducibility of titration of noble metal ions. The conditions are the same as for the titration of noble metal ions in their individual solutions, but with the content of the protolytic solvent in the analyzing range. As a consequence of lower solubility of the background electrolyte under these conditions to values less than 0.2 M under the influence of large additions of an inert solvent, the background concentration (with
40-50% volume of the inert solvent) must be continuously reduced up to values of the order of 0.05 M. The addition of any of the mentioned solvents in the amount of 10-20% volume (depending on the nature of the solvent) leads to the fact that the shape of the titration curve becomes less steeply inclined to the axis of the volumes, and at solvent contents higher than 50-60% volume reproducibility and accuracy of noble metal ions deteriorate.
The revealed effect of inert solvents on the form of the titration curve is explained by a sharp decrease in the electrical conductivity of the titrated solution at a high content of an inert solvent in the protolytic medium, leading to a significant and continuously increasing ohmic voltage drop in the analyzed solution with an increase in the indicator current.
Analysis of silver (I) and gold (III) ions in model mixtures. The possibility of amperometric titration of silver (I) and gold (III) with a solution of MPCMDPTC was tested on various artificial
mixtures of salts (simulating natural and industrial materials) containing large quantities of other metals, often and widely found with these metals in nature. Analysis of silver (I) and gold (III) ions can be done in two ways: 1) directly in an aliquot of the analyzed sample [10, 11.] with strict observance of all optimization conditions when assessing the degree of influence of various extraneous cations; 2) the combination of the preliminary extraction [12, 13] separation of silver (I) and gold (III) ions from other elements, followed by their titration with a standard solution of MPCMDPTC in an aliquot of the extract obtained after destruction of the extraction reagent and complex, and adding the required amount of protolytic solvent and background. The obtained results confirm that the developed amperometric methods for the determination of silver (I) and gold (III) ions by the solution ofMPCMDPTC differ by high selectivity and reproducibility with a relative standard deviation not exceeding 0.133.
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