European Journal of Scientific Research - EuroJournals

335 S. J. Fatemi, A. Badiei and A. Hooshmand
Figure 1: Absorbance of PDTC at various pH for determination of pka.
Effect of pH on Ni 2+ -PDTC binding
The effect of pH was studied by using 0.1 N HCl and 0.1 N NaOH. It was observed that the complex is
stable and absorbance was constant and maximum in the pH range 7.0-9.0 (fig. 2). Here hepes buffer
of pH 7.4 was selected for maintaining pH constant during the further studies.
Figrue 2: Effect of pH on Ni 2+ -PDTC binding,25°C [PDTC] ~ 10 -6 M.
Absorbance
0.16
0.12
0.08
0.04
Binding of Ni 2+ to PDTC
0
0 1 2 3 4 5
pH
6 7 8 9 10
The electronic absorption spectra of PDTC in hepes buffer solution within the region 200-600 nm
display two absorption bands (Fig. 3) (λmax, 250 nm and 276 nm). The first band is due to an enhanced
π�π * transition (K band) [17], while the second band could be attributed to an enhanced n�π *
transition (R band) [18-21].