Complexometric determination: Part II: Complexometric determination of Cu2+-ions

Abstract

A copper-selective electrode of the coated wire type based on sulphidized copper wire was applied successfully for determining Cu(II) ions by complexometric titration with the disodium salt of EDTA (complexon III). By the formation of internal complex compounds with the Cu(II) ion, the copper concentration in the solution decreases, and all this is followed by a change of potential of the indicator system Cu-DWISE (or Cu-EDWISE)/SCE. At the terminal point of titration, when all the Cu(II) ions are already utilized for the formation of the complex with EDTA, there occurs a steep rise of potential, thus enabling us, through the first or second derivative to note the quantity of copper that is present in the solution. Copper-selective electrode showed a responsivity towards titration with EDTA as a complexing agent, with the absence of "fatigue" due to a great number of repeated measurings. Errors occurring during quantitative measurements were more a characteristic of the overall procedure which involve, because of the impossibility of the complete absence of subjectivity, a constant error, and the reproducibility of the results confirmed this fact. The disodium salt of EDTA appeared as a very efficient titrant in all titrations and with various concentrations ot Cu(II) ions in the solution, with somewhat weaker response at lower concentrations in the solution.

U prvom delu rada prikazane su karakteristike dinatrijumove soli EDTA (kompleksona III), kao i mogućnost njene primene u kompleksometrijskim titracija-ma za kvantitativno određivanje različitih vrsta katjona, naročito Cu2+-jona. U drugom delu rada data je primena kompleksona III za određivanje bakra u vodenim rastvorima. Za određivanje završne tačke titracije korišćen je originalni tip jon-selektivne elektrode. Dokazana je primenljivost kompleksona III, teorijski objašnjena u prvom delu rada, za titrimetrijsko (kompleksometrijsko-potenciometrijsko) određivanje Cu2+- jona uz korišćenje indikatorskog sistema bakar-selektivna elektroda tipa prekrivena žica (modela DWISE i EDWISE)/ZKE, uz izraziti skok u završnoj tački titracije i dobru reproduktivnost rezultata određivanja.