Studies of Stability Constants of Several Metal Complexes with N-(2-Naphthyl)ethylenediamine-N, N', N'-triacetic Acid

Stability constants of Cd(II), Cu(II), Hg(II), Pb(II) and Zn(II) chelates with N-(2-naphthyl)ethylenediamine-N, N', N'-triacetic acid (NEDTA) were determined by spectrophotometric and fluorophotometric methods at 25±1°C. The composition of the NEDTA chelate with each metal ion was 1 : 1 both by the molar ratio and the continuous variation methods with spectrophotometry. The stability constants (log K) determined by the spectrophotometric method were as follows : Cd(II), 9.49; Cu(II), 14.62; Hg(II), 15.08; Pb(II), 11.77; and Zn(II), 11.00. Those by the fluorophotometric method were as follows : Cd(II), 9.67; Cu(II), 14.05; Hg(II), 15.93; Pb(II), 11.32 and Zn(II), 10.99.The conditional stability constants (log K') of these metal-NEDTA chelates at pH 4 were in the range of 6 to 11, which were large values compared to usual metal indicators. NEDTA shold be a useful indicator for microchelatometric titration and applicable to detection of a trace amount of several metal ions.