Application of Zetametry To Determine Concentrations of Acidic and Basic Impurities in Analytical Reagents

Abstract

The sign and magnitude of the ζ potential of mineral oxides in allegedly pure organic solvents (high-quality chemical reagents) depends on the concentration of acidic and basic impurities, chiefly organic acids and amines. "Zetametric titration" with HClO(4) makes it possible to estimate the concentration of basic impurities and offers an attractive alternative to other analytical methods. Titanium(IV) oxide has been chosen as the probe powder in view of its very low solubility and nearly neutral point of zero charge in aqueous systems. Some systems have a high buffer capacity and addition of acid and base has a minor effect on the ζ potential of titania. Specific adsorption of alkali metal cations on anatase can be also a significant problem.

Solvents, in which ionic surfactants do not affect the zeta potential

“…The f potentials determined by electroacoustic method at high solid-to-liquid ratios are less sensitive to surface-active impurities present in non-aqueous solvents, which affect the f potentials obtained by electrophoresis [9]. Both the solid particles and allegedly pure solvents contain surface-active impurities, and nature and concentration of surface-active species in the dispersion depend on the solid-to-liquid ratio.…”

Dispersions of Anatase in Ambient Temperature Ionic Liquids

“…), but the mobility values were rather scattered and always much smaller in absolute value than the half-width of the mobility histogram. Striking results of traces of water on the electrokinetic potential of anatase (8) and other oxides (9) in organic solvents have been reported, but in these studies the sign was reversed from negative to positive on addition of water.…”

“…High ζ potentials of oxides in allegedly pure organic solvents are due to the presence of acidic or basic impurities in these solvents, and neutralization of these impurities by mineral acids or bases often leads to reversal of sign of the ζ potential (8). The effect of inorganic solutes (NH 3 , NaOH, HCl) on the electrokinetic behavior of anatase was also studied in EMIBF 4 .…”

Electroacoustics in low-temperature ionic liquids

“…It has been shown [11] that even dehydration or very precise control over the level of humidity does not solve all the problems related to reproducibility of mobilities in nonaqueous systems, and the present approach allowed us to reduce the amount of LTIL to about 50 g per one mobility value.…”

“…[8] for detailed discussion) with the difficulties related to measurements in nonaqueous media. Namely, the numerical values of ζ potentials in organic solvents are severely affected by traces of water and other surface-active impurities [11], whose concentration is difficult to measure or control, and often even their nature is unknown. Then the approach to the problem of ambient moisture must be addressed in any experiment related to electrokinetics in nonaqueous systems.…”