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AMPEROMETRIC TITRATION OF PALLADIUM (II) AND PLATINUM (IV) IONS IN INDIVIDUAL SOLUTIONS OF VINYLPYRIMIDINE
Rakhmatov Khudoyor Boboniyozovich, Senior lecturer of machinery and equipment department of the Karshi Engineering Economic Institute Quarshi city, Uzbekistan E-mail: zavod.lab.@mail.ru Zhavliev Furkat Bakhtiyorovich, Assistant at chemistry department of the Karshi Engineering Economic Institute, Quarshi city, Uzbekistan
Kuybokarov Oybek Ergashyevich, Assistant at oil and gas refining technology department of the Karshi Engineering Economic Institute Quarshi city, Uzbekistan
Abdirazzakov Akmal Ibragimovich, Senior professor of oil and gas field development and operation department of the Karshi Engineering Economic Institute Quarshi city, Uzbekistan Dustkabilov Eldor Nurmamatovich, Senior professor of oil and gas refining technology department of the Karshi Engineering Economic Institute Quarshi city, Uzbekistan
AMPEROMETRIC TITRATION OF PALLADIUM (II) AND PLATINUM (IV) IONS IN INDIVIDUAL SOLUTIONS OF VINYLPYRIMIDINE
Abstract. The article describes the conditions for and the possibility of amperometric titration of palladium (II) and platinum (IV) ions in individual solutions of vinylpyrimidine (VP) in non-aqueous media (acetic acid, n-propanol, DMF, DMSO) and their mixtures with background electrolytes with different acid-base properties. The article proposes methods of amperometric titration of microgramic quantities of palladium (II) and platinum (IV) ions in individual solutions.
Keywords: palladium, platinum, vinylpyrimidine, solution, acetic acid, n-propanol, DMF, DMSO, background electrolytes, amperometry.
Amperometric titration of metal ions in non-aqueous and mixed media with various complexants allows expanding their analytical capabilities and simplifying the solution of many complex analytical problems. One of the important factors for this is the fact that the nature of the solvent heavily influences the strength of the resulting complex, moreover, it is not the same for different cations, which determines the selectivity and expressivity of the method. In addition, methods of non-aqueous complexometry successfully solve the problem of accurate and selective determination of metals in organic objects, as well as directly in the extracts obtained by concentration.
We tried to find optimal conditions for amperometric titration of a number of noble metals with solutions of vinylpyrimidine (VP) in non-aqueous protolytic media with different acid-base properties of background electrolytes.
Reagents and equipment. The original 0.002 M solutions of Na2PdCl4, K2PtCl6, as well as 0.01 M solution of VP were prepared by dissolving the reagents of appropriate weight in acetic acid (n-propanol, DMF and DMSO). The concentration of noble metals was determined amperimetrically by using a 0.01 M solution of potassium iodide [1]. Amperometric titration was carried out on a device with two rotating (1000 rpm) platinum wire electrodes on a common axis. The structure of electrodes, automatic piston microburettes and apparatus are described in detail in [2].
Amperometric titration was carried out on a device with two rotating (1000 rpm) platinum wire electrodes on a common axis. The structure of electrodes, automatic piston microburettes and apparatus are described in detail in [3].
According to voltamperometric behavior of VP and other products participating in electrochemical environments,
Section 13. Chemistry
amperometric titration of noble metal ions should be carried out at a polarization voltage of 0.75-1.15 V, depending on the nature and concentration of the background electrolyte (acetates, nitrates, chlorides, alkaline metals and ammonium) [4]. The indicator current should occur beyond the equivalence point (e.p.) due to oxidation of the free reagent and reduction of the dissolved oxygen in the air.
Experimental data showed that in the studied media and backgrounds of 0.15-0.40 M solutions of noble metals ions with VP solutions titrated well and fast enough, and the shape of the curve coincides with the expected with only some constant current at the beginning of the titration followed by a sharp transition (curve) at the end point of titration (EPT).
Determination of palladium (II) and platinum (IV) ions in individual solutions. It was found that during the titration of the following noble metals ions, the corresponding molar ratio metal/reagent is: Pd/reagent 1/2 and Pt/reagent 1/4, the titrated solution gains reddish-brown color. During the transition from acetate to perchlorate backgrounds 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 reproducibility and correctness of results. This is explained by an increase in the acidity of the analyzed medium during the transition from acetates to perchlorates [5]. Some of the data obtained are shown in the table.
Table. Results of amperometric titration of various number of palladium (II) and platinum (IV) ions with solution of VP in DMSO on 0.20 M lithium perchlorate background
Introduced metal, Found metal, ^g (Р = 0,95; х ± ДХ) n S S
Pd 15.44 15.423 ± 0.16 3 0.061 0.00 4
Pt 30.88 30.854 ± 0.12 4 0.052 0.002
Pd 61.75 61.782 ± 0.18 3 0.033 0.001
Pt 123.50 123.494 ± 0.20 4 0.102 0.001
Pd 247.00 246.951 ± 0.41 4 0.213 0.001
Pt 493.10 493.793 ± 0.52 3 0.624 0.001
The results of the different concentrations of noble metal ions determination with a solution ofVP in 10.0 ml of the test solution under optimal conditions indicate a good accuracy of the developed technique. The effect of additives to acetic acid, n-propanol, DMF, DMSO on the correctness and reproducibility of titration of noble metal ions was studied for such inert solvents as chloroform, carbon tetrachloride, benzene, toluene, hexane, methyl ethyl ketone, dioxane, etc., which are often used as extractants. Conditions, as in the titration of noble metal ions in their individual solutions, with the difference that the content of the protolytic solvent in the analyzed sample was regulated strictly according to the volume of the added inert solvent. Due to the decrease in the solubility of the background electrolyte under these conditions to values less than 0.2 M, under the influence of large additives of an inert solvent, the background concentration (with 40-50% by volume of inert solvent) must be continuously reduced
back to values of the order of 0.05 M. Adding any of these solvents in the amount of 10-20% of volume (depending on the solvent) has almost no influence on the shape of the titration curve, which becomes less steeply inclined to the axis of the volumes. For the same reason, when the content of the solvent is above 50-60% of volume, the reproducibility and accuracy of the definitions of the noble metal ions deteriorate.
The revealed nature of the influence of inert solvents on the type of titration curve is explained by the decreasing electrical conductivity of the titrated solution with a high content of inert solvent in the protolytic medium, resulting in a significant and continuously increasing ohmic drop in the analyzed solution with increasing indicator current.
Consequently, amperometric methods for the determination of palladium (II) and platinum (IV) ions with VP solution are distinguished by high selectivity and reproducibility with a relative standard deviation not exceeding 0.004.
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