Polarographic Studies of Cadmium(II) Complexes with N, INP-Bis(2hydroxyethyl)ethylenediamine-N, N'-diacetic Acid

• Published in: Nippon Kagakukai shi (1972) Vol. 1981; no. 8; p. 1265
• Main Authors: MATSUO, Tsutomu, MASUDA, Yoshitaka, SEKIDO, Eiichi
• Format: Journal Article
• Language: English
• Published: Tokyo Japan Science and Technology Agency 01.08.1981
• ISSN: 0369-4577

The polarographic behaviour of Cd (II) ion in EDDA (OH)2 (N, N'-bis (2-hydrOxyethyl) ethylenediamineN, N'-diacetic acid) solutions with metal ligand ratios of 0.5: 1, 1: 1, and 1: 5in the pH range from 3.12 to 8.77 was investigated. Those polarograms gave one or two well-defined waves by the experimental conditions employed. The first wave (-0.596 V vs. SCE, pH=4.05, the reciprocal slope of log-plot: 30.3 mV) was due to the reversible reduction of free Cd(II) ion. It was shown that the second wave (-0.958 V) for the reduction of the complex species, CdL or CdHL+ is irreversible and the limiting current is diffusion-controlle d (the reciprocal slope: 55.9mV, ij ∝ h1/2+corr. )Formation of the complex species (ML) with a ratio of 1: 1 was confirmed from the data of the amperometric titrations. The dependence on pH for the half-wave potential of the second wave, showed that the complex species participating in the electrode reaction was changed from CdHL+ to CdL near pH= 4.4. The electrode reaction mechanisms of the second wave are as follows; pH≤4.4, CdHL+ + H+ + 2e Hg ->kj1 Cd(Hg) H2 L (I) pH>4.4, CdL+ 2e + Hg ->kj2 Cd(Hg) + L2- (II) where kji denotes the reaction rate constants. The stability constant, KcdHL, was calculated to be 105.6 by using an equation proposed by Vlcek. The values of Kji for mechanisms ( I ) and were also determined to be kj1=6.9 × 10-6cm/s and kj2= 1.2 × 10-6cm/s, respectively. T(IhIe)frequency dependence of the "cut-in" height in the oscillopolarogram was increased in the order of the complexes: <CdHL+: This was in the reverse order of the stability constant.