The double layer potentials at the toluene–aqueous interface in the presence of CTAB/NaBr. Implications for Ion-Selective Electrodes

On the origin of the Hofmeister effect in anion-selective potentiometric electrodes with tetraalkylammonium salts

“…In our previous paper [29] we showed that the potential of the Stern layer, which is determined by the structure of the mixed (cations + anions) monolayer adsorbed at the liquid-liquid interface, agrees well with the potentiometric response of ''blank" ISEs (containing no added lipophilic salts or ionophore) to the same surfactant present in the aqueous phase. The Stern potentials were calculated using the Surface quasi-Two Dimensional Electrolyte (STDE) model of Warszynski et al [30,31], from the interfacial tension data for cetyltrimethylammonioum bromide (CTAB) at the aqueous-toluene interface, in the absence of added salt.…”

“…3) is consistent with adsorption of the surface active ions, cetyltrimethylammonium and dodecylsulfate, respectively, at the membrane-aqueous interface. We have shown previously that a concentration dependence of the electrical potential of membrane-based ISEs is very similar to that of the Stern potential (W S ) calculated from the interfacial tension data at the toluenewater interface [29]. The Stern potentials calculated with help of STDE model for CTAB and SDS from the interfacial tension measurements at toluene-water and air-water interfaces, respectively are shown as solid lines in Fig.…”

“…The effect of added NaBr salt on the interfacial tension at the toluene-water interface at fixed concentrations of CTAB has been thoroughly studied and discussed in the previous paper [29]. The addition of NaBr significantly decreases the interfacial tension due to screening of electrostatic repulsion between the CTA + cations adsorbed in the monolayer.…”

“…In addition, it can be easily adapted to the adsorption of CTAB at toluene-aqueous interface [29]. The details of the model were described in [30,31], below we present only its major features:…”

A New Device for Simultaneous Measurements of Dynamic Interfacial Tension and Electrical Potential Difference

“…In two separate experiments (one for IT and one for EMF measurements) we previously found that the adsorption of CTAB at the aqueous organic interface accompanies the electrical potential response of an ISE. 11 The present setup allows for simultaneous measurements of both parameters using the same solutions ( Figure 2). Upon formation of each new drop of CTAB solution, the IT starts to decrease, and the EMF starts to increase, as a result of accumulation of positively charged CTA + ions at the interface.…”