Vol. 2, Issue 3 (2018)
Extraction-spectrophotometric study of ternary complexes of Cr (VI) and Co (II) Using o-Hydroxythiophenols and Aminophenol
Author(s): Shahla A Ibrahimova, Ali Z Zalov, Novrasta S Hasanova
Abstract: The following reagents were used: thiocatechols (TCs, H2L):2-hydroxy-5-bromothiophenol (HBTP), and 2-hydroxy-3-thiolsulphonic asid (HTSA); and hydrophobic amines (HAs): -2,6-bis (N, N-dimethylaminomethyl) -4-methylphenol (AP1) and 2,6-bis (N, N-dimethylaminomethyl) -4-chlorophenol (AP2). The TCs were characterized by physicochemical methods: IR and NMR spectroscopy. To elucidate the oxidation state of chromium in the presence of TCs, we conducted two series of experiments. In the first series we used Cr(VI), while in the second series we used Cr(III) obtained by addition of a supplementary reducing agent (SnCI2 or KI). The comparison of the obtained spectra showed that λmax Cr(VI) - TCs = λmax Cr(III) - TCs. This fact can be regarded as an indication that Cr(VI) is reduced to Cr(III) by the reagent itself during the complex formation.After a single extraction with chloroform, 97.4-98.8% of сhromium and cobalt was extracted as an ion associate. For the formation and extraction of chromium (III) and cobalt (II) complexes, pH 2.9-4.9 and 3.3-6.8, respectively, are optimal. The optimal condition for the formation andexpression of these codents is concentration (1.3-1.5) × 10-3 M TCs and (1.2-1.5) × 10-3 M HAs. Extracts of Cr3+ and Co2+ radionuclides obey the basic law of light absorption at concentrations of 0.2-20 and 0.2-22 μg / ml, respectively. The maximum optical density of chromium (III) complexes and cobalt (II) is reached within 12 and 10 minutes, respectively. The absorption maxima of the Cr (III) - HBTP-HAs triple complexes lie in the range 437-440 nm (in the case of cobalt 545-560 nm). The molar absorption coefficients for chromium complexes (2.70 - 2.74) × 104 L×mol-1 × cm-1 (in the case of cobalt (3.43 - 4.14) × 104 L × mol-1 × cm-1). The molar relationships between the components of the ternary complex were found by several methods: the method of relative profitability of the old Barbanel, the linear method, and the equilibrium shift method (Cr:TCs:Has = 1:3:3 and Co:TCs:Has = 1:2:1). It was established by Nazarenko's method that the complexing form of chromium (III) and cobalt (II) is Cr3+ and Co2+, respectively. The calculations showed that the MLC in the organic phase does not polymerize and is in monomeric form (γ = 1.01-1.05). It has been established that large amounts of alkali, alkaline earth elements, rare earth elements, F-, CI-, Br-, SO32-, SO42- and C2O42- do not interfere with the determination of chromium and cobalt. The selectivity of the determination is significantly increased in the presence of masking agents. The proposed method, within the established optimal conditions, was used to determine Cr (III) and Co(II) in milk, sour cream and cottage cheese.