The sorption of procaine and bupivacaine from aqueous solutions by Nafion membranes modified with PEDOT

Abstract

Local anesthetics, procaine (2-(diethylamino)ethyl-4-aminobenzoate) and bupivacaine ((RS)-1Butyl-N-(2,6-dimethylphenyl)-pyridine-2-carboxamide) hydrochloride are widely used in medicine. Various sorption materials and methods are used for their identification. It was demonstrated earlier that the introduction of poly(3,4-ethylenedioxythiophene) (PEDOT) to Nafion perfluorosulfonic acid cation exchange membranes reduced the interfering effect of hydroxonium ions on the response of Dp-sensors in local anesthetics solutions. The modification has an opposite effect on the sensitivity of PD-sensors to cations of procaine and bupivacaine. It is therefore important to study the sorption properties of these materials in local anesthetics solutions for further optimisation of the sensors’ characteristics. The aim of our research was to study the sorption of procaine and bupivacaine cations from aqueous solutions byNafion-117 membranes modified with PEDOT. The study demonstrated that the moisture content in Nafion-117 and Nafion-117+PEDOT membranes in equilibrium with the local anesthetics solutions decreases due to the presence of three-dimensional cations with hydrophobic fragments. The substitution of protons with organic cations is limited by the steric factor. The moisture content of membranes in equilibrium with a BupHCl reduces by 1.4-1.8 times as compared to the sample in the Н+ form. Concentrations of the absorbed procaine cations and desorbed protons are compatible within the measure of inaccuracy. The moisture content of membranes in equilibrium with a ProHCI solution reduces by 3.7-4.7 times as compared to the initial. The concentration of desorbed hydroxonium ions is lower than the concentration of absorbed procaine ions. Furthermore, the growth of the concentration of PEDOT in the membrane has the opposite effect on the sorption of procaine and bupivacaine from aqueous solutions. A possible cause of such an interaction between the ions of local anesthetics and membranes (including the ones containing a dopant with π-πconjugation) is the location of the functional groups in the cation structure. As a result, procaine cations tend to form dimers and micelles in aqueous solutions, while bupivacaine cations do not have this feature.