Suspension effect in gels in view of its new concept

Abstract

The suspension effect (SE) observed in potentiometric measurements in gels is in accordance with the suspension effects measured in heterogeneous suspensions. The SE depends on processes at the indicator electrode (PWSE) and on the consequences of the imperfection of the reference electrode (OSE). Together, these represent the originally defined suspension effect (ODSE). The PWSE is considered to be due to the change of the potential forming mechanism of the indicator electrode in the real solution (simple electrode) compared to the different one in a suspension or a sediment (double electrode). The PWSE, expressed as a change of voltage, has only small values, whether measured in organic or inorganic gels. OSE values (as voltage changes) are greater but still several times smaller than in the suspensions of ion exchangers. OSE were obtained from the Donnan emf, measured according to the common practice, neglecting the junction potential of the sce immersed in the equilibrated supernatant solution. In this case the Donnan emf is identical with the “anomalous liquid junction” potential, which in our SE concept is considered as the potential of the “leaky membrane”. The Donnan potential at the equilibrium solution/sediment interface is regarded as negligible or zero. This is argued from the negligible Donnan emf values obtained when the “anomalous liquid junction” is destroyed by agitation of the sce salt bridge, immersed in the sediment of the Donnan cell. From this point of view some recent opinions declaring the Donnan potential to be the main contributor to the SE are discussed. Another mode of Donnan emf measurement, specified by the reversed flow of KCl solution in sce salt bridges, shows zero voltage values. A detailed galvanic cell diagram must be used for a valid unambiguous interpretation of these voltage values.