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(17-10) Calculating methods in analysis of cobalt and nickel speciation: possibility and limitation. Linnik, Rostyslav*,1, Zaporozhets, Olga1, 1 National Taras Shevchenko University, Volodymyrska Str., 64, Kyiv, Ukraine ABSTRACT- The interest in determining the levels of individual compounds of heavy metals in aquatic environment arises from the recognition that transfer processes, bioavailability and toxicity are highly dependent on the element speciation. The aim of our study is to determine the ratio of free cobalt and nickel ions and complexes with dissolved organic matter, especially with the fulvic acids as dominated ligands in Dnieper reservoirs. Calculating methods based on stability constants of metals with inorganic and organic ligands were used for determination of cobalt and nickel species. It was established that correct data on coexisting forms of investigated metals depend on a choice of the reliable stability constants of metal complexes with fulvic acids. So long as stability constants may vary strongly in depending on the ionic strength and ionic composition of the aquatic environment, it is necessary to check calculating data by experimental methods. The methods of membrane filtration, gel permeation and ion-exchange chromatography in combination with chemiluminescence detection were also used to separate and determine cobalt and nickel coexisting forms in water samples from Dnieper reservoirs. It was found that dissolved forms of cobalt and nickel in Dnieper reservoirs are for the most part organic complexes. Fulvic acids play the principal role in complexation. Share of fulvic acids complexes of Co (II) and Ni (II) reaches 57-77 and 63-85 % accordingly. If the logarithm of stability constants of fulvic acids complexes of both metals is 6.46 (Co) and 6.70 (Ni), in this case calculating data about cobalt and nickel speciation are in good agreement with experimental results. Key words: speciation, cobalt, nickel, fulvic acids |
