2. pH-effect

The potential changes versus different pH values for the DEP-membrane electrode type I and type II were tested. In acidic part, the break was observed at pH values 3.8 and 3.2 for type I and II electrodes, respectively. The sensitivity of β-CDX toward the H<sup>+</sup> is the reason for the potential break in acidic medium. The break in acidic medium was due to the inclusion of H<sup>+</sup> into ionophore in the membrane site. Above pH 3.2 and 3.8, the potential was not changed whatever the pH value for types I and II, respectively. This was due to the absence of the H+ ion concentration, which disturbs the equilibrium. Representative curves for nickel with membrane types I and II are shown in Figure 7.

Figure 7. pH-effect for Ni electrode for 0.001 M Ni2+ solutions for electrodes comprising (a) DEP and (b) NPOE.
