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The effect of 1-decanol on the potentiometric response of three ion-selective electrodes to large cationic species is analyzed. The electrodes were constructed with plasticized PVC membranes. The results suggest that 1-decanol alters the ionic transport through the membrane/water interface to an extent that depends on the strength of the active ion pair. The water solubility of the cation, its molecular weight, and the size of the ion pair seem to be relevant factors in this type of behavior. The potentiometric selectivity coefficients are also dependent on the presence of 1-decanol in the membrane. These results are similar to those already described in ion-selective electrodes with membranes capable of sensing anionic benzene sulfonate-type systems. Thus, the effect of the alcohol appears to be general by affecting mainly the membrane surface polarity.

The surface properties of poly(mono‐n‐alkylmaleate‐alt‐N‐vinyl‐2‐pyrrolidone) sodium salts derivatives with n=8, 10, 12, 16, and 18 carbon atoms in the side chain were analyzed. The surface tension behavior suggests that the adsorption at the surface is competitive with the polyelectrolyte “micellization” in the bulk. In fact, polyelectrolytes containing shorter side chains are more active at the surface than are polyelectrolytes with larger lateral chains. The contributions to the standard free energy of the adsorption process, related with their efficiency and effectiveness, were +1.07 kJ and −0.61 kJ per mole of methylene group, respectively. A positive value for the incremental free energy suggests that the gradual addition of methylene groups to the polyelectrolyte side chain actually stabilizes the polyelectrolyte in the bulk solution, whereas a negative value makes the packing process of the polyelectrolyte hydrophobic tails more spontaneous in an arrangement normal to the surface.

The influence of decyl alcohol on the potentiometric response of three para-alkylbenzenesulfonate (p-RBS) electrodes is analyzed. The results are clearly dependent on the membrane surface polarity due to the presence of the alcohol. The ionophore was the complex trioctylmethylammonium–p-RBS, (TOMA+)–p-RBS−, with R = H , CH3, and C2H5. The nature of the complex plays a fundamental role on the potentiometric behavior of the electrode showing that the more hydrophobic the complex, the better the potentiometric responses. Moreover, the electrodes selectivities for several hydrophilic and hydrophobic interfering anions were determined. The potentiometric results with interfering anions were coherent with the Pearson's hard and soft acid–base character of these anions.

The interfacial properties of poly(maleic acid-alt-1-alkene) disodium salts at hydrocarbon/water interfaces are determined. In all the studied systems, the interfacial tension decreases markedly with the polyelectrolyte concentration as the side-chain length increases. The results of the standard free energy of adsorption, DeltaG(ads)(0), are a linear function of the number of carbon atoms in the polyelectrolyte side chain. The contribution to DeltaG(ads)(0) per mol of methylene group varies from -0.64 to -0.52 kJ/mol for the n-octane/water to n-dodecane/water interfaces. DeltaG(ads)(0) data also reveal that the adsorption process is mainly determined by adsorption efficiency. Comparatively, the adsorption effectiveness seems to play a less important role. The theoretical interaction energies calculated for the insertion of one hydrocarbon molecule into the space formed by two neighboring polyelectrolyte side chains are in good agreement with the experimental results. The latter results are consistent with van der Waals-type interactions between the hydrocarbon molecules and the polyelectrolyte side chains.

The surface properties of poly( N -monoalkylmaleamic acid-alt-styrene) sodium salts are studied as a function of the molecular weight and the size of the linear alkyl lateral chain of the polyelectrolyte. The experimental results are well described by the Gibbs–Szyszkowski treatment. Both the surface tension behavior and the standard free energy of adsorption depend on the polyelectrolyte side chain and on the average molecular weight, M w . An M w -dependent contribution to the free energy of adsorption ranging from −1.21 to −1.05 kJ for mole of methylene groups is found. The area covered by monomer units increases with M w and the sizes of side chains are similar to those reported in small-molecule systems. The nature of the functional group amide in the side chain has practically no effect on the surface properties as compared with the ester group in this kind of polyelectrolytes.

The effect of phenols containing different electron-withdrawing substituents on the potentiometric responses of several liquid PVC membranes containing the complex trioctylmethylammonium–nitrate, TOMA+NO3−, is analyzed. The results make it possible to separate these phenols into two groups; those phenols containing electron-releasing groups, which produce almost Nernstian slopes, and those containing electron-withdrawing substituents, which generate sub-Nernstian slopes. The highly negative standard free energy of transfer of the aryl phenolic group from water to a cationic polar head suggests that these phenols are mainly located in the membrane phase associated with TOMA+ via a cation–π interaction. It seems that the strength of this interaction, and hence of the nitrate dissociation, is affected by the presence of phenols in an extension which correlates well with the kind of phenol present in these membranes and, consequently, with the type of their potentiometric responses.

An isopropyl xanthate ion-selective electrode was constructed using as a carrier the complex trioctylmethylammonium-isopropyl xanthate. Two kinds of plastic membranes were built, with dioctyl phthalate (DOA) and dioctyl adipate as plasticizers. In both cases, the electrical responses were linear in a wide range of xanthate concentrations, with the limit of detection between 10(-4) and 10(-5) M. The electrical response was improved by adding only 3mgr;mol of dodecyl alcohol per membrane. This fact seems to indicate not only that the fluidity is relevant but also that the surface polarity of the plastic membrane plays an important role. The analysis of some added salts shows that isobutyl xanthate is a strong interfering agent for the DOA electrode. Nitrate interferes weakly, whereas chloride, acetate, and carbonate do not affect the electrical response of both kinds of electrodes. Copyright 2001 Academic Press.

Surface properties of aqueous mixed micelles formed by hexadecyltrimethylammonium bromide (CTABr) and the nonionic surfactant polyoxyethylene 23 lauryl ether (Brij 35) have been studied. The Br− and CTA+ intermicellar activities have been measured by using specific electrodes for both ionic species. When log(aCTA+) are plotted vs log(aBr−) linear relations are obtained and the slopes of the plots are used to calculate the degree of dissociation (β) for the different molar fractions of the CTABr-Brij 35 mixed micelles. Surface micellar potentials (Ψ0) were also calculated, compared with reported values, and related with the experimental β values. β was found to be an almost linear function of Ψ0. Mean activities for the intermicellar CTA+ and Br− ions were also calculated. The obtained mean activities suggest that the CTA+ monomers are preferentially sorbed by micelles richer in the nonionic surfactant. CMCs of the mixed micelles, calculated from the electromotive force of the CTA+ electrode are in very good agreement with CMCs values reported for the same systems.

A new, rapid, and simple method for preparing long-chain alkyltrimethylammonium (A1TA+X−) or long-chain alkylpyridinium (A1Py+X−) salts (X− = F−, Cl−, Br−, NO3−, SO42−, PO42−, car☐ylic anions, etc.) is presented. The method is based on the preparation of a water-insoluble xanthate formed between an A1TA+X− or an A1Py+X− (X− = Cl− or Br−) with an alkyl xanthate followed by decomposition of the xanthate in acidic medium according to the reaction: A1TA+(xanthate) + H+X− → CS2 + ROH + A1TA+X− (R stands for the alkyl chain of the xanthate). Therefore, addition of H+X− to A1TA+ (xanthate)− will give a quaternary ammonium salt containing X− as a counterion. Cetyltrimethylammonium ethyl xanthate was used in this work and cetyltrimethylammonium chloride, bromide, and nitrate were obtained by adding HCl, HBr, or HNO3 to the cetyltrimethylammonium ethyl xanthate. Analysis of Cl−, Br− CTA+ content and critical micelle concentrations of the prepared compounds gave results in excellent agreement with expected values. The method is quite general and can also be applied to obtain polyelectrolytes carrying quaternary ammonium ionogenic groups.