Current-polarized ion-selective membranes: The influence of plasticizer and lipophilic background electrolyte on concentration profiles, resistance, and voltage transients

Abstract

Lipophilic background electrolytes consisting of a lipophilic cation and a lipophilic anion, such as tetradodecylammonium tetrakis(4-chlorophenyl) borate (ETH 500), or bis(triphenylphosphoranylidene) ammonium tetrakis[3,5bis(trifluoromethyl) phenyl] borate (BTPPATFPB) are incorporated into the membranes of ion-selective electrodes (ISEs) to improve the detection limit and selectivity of the electrodes and decrease the resistance of the sensing membrane. In this work, spectroelectrochemical microscopy (SpECM) is used in conjunction with chronopotentiometry to quantify the effects of a lipophilic background electrolyte on the concentration profiles induced inside current-polarized membranes and on the measured voltage transients in chronopotentiometric experiments. In agreement with the theoretical model, the lipophilic background electrolyte incorporated into o-NPOE or DOS plasticized membranes decreases the membrane resistance and thus the contribution of migration in the overall transport across ion-selective membranes. Consequently, it has a significant influence on the changing concentration profiles of the ion-ionophore complex during chronopotentiometric experiments.

Interpretation of chronopotentiometric transients of ion-selective membranes with two transition times

“…Diffusion coefficients have been calculated previously for free and complexed ETH5234 from chronoamperometric ( D L =2.3 × 10 −8 cm 2 /s) and potentiometric ion breakthrough experiments $(D_{{\text{IL}}_{\mathrm{normalk}}^{\mathrm{n}+}}=0.85\times {10}^{-8}{\text{cm}}^2/\mathrm{s})$, respectively [3]. The TFPB − anion diffusion coefficient inferred from SpECM measurements is D R − = 1.1 × 10 −8 cm 2 /s [24]. By using these diffusion coefficients in combination with Eqs.…”

“…The concentration profiles in neutral ionophore-based cation-selective membranes during an applied current step have been described previously. The membrane formulations for which the theory is derived consist of a plasticized polymeric matrix that incorporates the ionophore and a mobile cation exchanger (lipophilic anion) [7, 23, 24]. Eqs.…”

“…The equations for the ion-ionophore complex breakpoint were derived with the assumption that ion-pair formation between the ion-ionophore complex and the mobile anionic ion-exchanges sites inside the membrane is negligible [24]. …”

Flow Injection Potentiometric Determination of Pancuronium Bromide in Pharmaceutical Preparation and Urine Samples Using Modified Carbon Paste Electrodes

“…0.5% Tetradodecylammonium tetrakis-(4-chlorophenyl)borate as lipophilic additives was added (Table 1). The results showed that the carbon paste electrode with ion-pair ratio of 5% has the best performance characteristics (slope, 28 28) The influence of plasticizer type on the performance characteristics of Panc sensors was investigated by using four plasticizers with different polarities (DBP, DOP, DOS, and TCP). The results reveal that DBP is the best of the plasticizers tested.…”

Assessment of Ion‐Ionophore Complex Diffusion Coefficients in Solvent Polymeric Membranes

“…The equations for the ion-ionophore complex were derived with the assumption that ion-pair formation between the ion-ionophore complex and anion is negligible inside the membrane [21]. The equations are different for membranes without ion-ionophore complex migration, i.e., for membranes loaded with an excess of lipophilic electrolyte [3].…”