Numerical values of the electrokinetic potentials of anatase at high concentration of NaI

The electrokinetic potential of anatase (titanium dioxide) in 0.3, 0.5, and 1 mol dm(-3) NaI was studied by means of AcoustoSizer 1, AcoustoSizer 2 and DT-1200. Different stirring modes were studied for DT-1200. The increase in the electrolyte concentration produced a shift in the IEP of anatase to higher pH, and for 1 mol dm(-3) NaI there was no IEP at all, and the electrokinetic potential was positive over the entire pH range. The shifts in the IEP observed by means of different instruments were qualitatively consistent. On the other hand, the numerical values of the electrokinetic potentials of anatase at high concentration of NaI at low pH obtained by means of Acoustosizer 2 were substantially higher than those obtained by means of DT-1200. The discrepancies in the numerical values of the electrokinetic potentials obtained by means of different instruments increase as the ionic strength increases. The procedure of correction for the electroacoustic signal of the electrolyte is probably the main source of the discrepancies between DT-1200 and Acoustosizer at high ionic strengths. The difference in the efficiency of mixing in different stirring modes plays rather insignificant role in the observed discrepancies.