A growing interest in dental practice in intranasal anesthesia using tetracaine and oxymetazoline dictates the need for their simultaneous determination in combination drugs and human saliva. Potentiometric multisensory systems based on perfluorosulfonic acid membranes, including polyaniline-modified ones, were developed for these purposes. A change in the distribution of the sensor sensitivity to the related analytes was achieved by variation of the conditions for concentration polarization at the membrane interface with a studied solution due to a change in the intrapore volume, nature, and availability of the sorption centers, as well as the hydrophilicity of the membrane surface that were specified by the conditions for their synthesis and subsequent hydrothermal treatment. Reversibility of the analyte sorption using the chosen conditions for regeneration provided long-term stable work of both the sensors and the calibration equations established by multivariate linear regression. The membrane modification promoted their resistance to fouling. The relative errors of the simultaneous tetracaine and oxymetazoline determination in the combination drug solutions were no greater than 7% and 11%, while in the artificial saliva solutions, they were 15% and 17%, respectively, when an array of the cross-sensitive sensors based on the composite membranes prepared by different methods was used. The analysis errors were reduced to 3%-6% when analyzing the drug and to 0.2%-6% when analyzing the artificial saliva if an array was organized with the sensors based on the membrane with the dopant and the membrane without it, due to the decreasing correlation between their responses. Potentiometric multisensory systems based on perfluorosulfonic acid membranes, including polyaniline-modified ones, were developed for the simultaneous determination of tetracaine and oxymetazoline in combination drugs and human saliva. Reversibility of the analyte sorption during regeneration provided long-term stable work of the sensors and calibration equations established by multivariate linear regression. The analysis errors were 0.2%-6% for the sensor array based on the membrane with polyaniline and the one without it, due to the low correlation between the responses.

The phenomenon of concentration polarization (CP) in membrane systems refers to the emergence of concentration gradients in solution near the membrane surface due to the selective transport of some solution components through the membrane under the effect of transmembrane driving forces. CP accompanies all types of membrane processes, changing transport conditions and reducing efficiency of separation processes: in most cases, the total transport rate decreases, the energy consumption increases, and the selectivity of the transport process is lost. This review addresses general regularities and specific features of the CP phenomenon in electrodialysis, reverse osmosis, nanofiltration, ultrafiltration, and pervaporation processes, as well as membrane sensing systems and fuel cells. Fundamentals of the CP phenomenon and experimental methods for its investigation are discussed.

The degradation of drugs is a substantial problem since it affects the safety and effectiveness of pharmaceutical products, as well as their influence on the environment. A novel system of three potentiometric cross-sensitive sensors (using the Donnan potential (DP) as an analytical signal) and a reference electrode was developed for the analysis of UV-degraded sulfacetamide drugs. The membranes for DP-sensors were prepared by a casting procedure from a dispersion of perfluorosulfonic acid (PFSA) polymer, containing carbon nanotubes (CNTs), whose surface was preliminarily modified with carboxyl, sulfonic acid, or (3-aminopropyl)trimethoxysilanol groups. A correlation between the sorption and transport properties of the hybrid membranes and cross-sensitivity of the DP-sensor to sulfacetamide, its degradation product, and inorganic ions was revealed. The analysis of the UV-degraded sulfacetamide drugs using the multisensory system based on hybrid membranes with optimized properties did not require a pre-separation of the components. The limits of detection of sulfacetamide, sulfanilamide, and sodium were 1.8 × 10−7, 5.8 × 10−7, and 1.8 × 10−7 M. The relative errors of the determination of the components of the UV-degraded sulfacetamide drugs were 2–3% (at 6–8% relative standard deviation). PFSA/CNT hybrid materials provided the stable work of the sensors for at least one year.

The development of accessible express methods to determine markers of viral diseases in saliva is currently an actual problem. Novel cross-sensitive sensors based on Donnan potential with bio-comparable perfluorosulfonic acid membranes for the determination of salivary viral markers (N-acetyl-L-methionine, L-carnitine, and L-lysine) were proposed. Membranes were formed by casting from dispersions of Nafion or Aquivion in N-methyl-2-pyrollidone or in a mixture of isopropyl alcohol and water. The influence of the polymer equivalent weight and the nature of dispersing liquid on water uptake, ion conductivity, and slope of Donnan potential for the membranes in H+ and Na+ form was investigated. The varying of the sorption and transport properties of perfluorosulfonic acid membranes provided a change in the distribution of the sensor sensitivity to N-acetyl-L-methionine, L-carnitine, and L-lysine ions, which was necessary for multisensory system development. The simultaneous determination of three analytes, and the group analysis of them in artificial saliva solutions, was performed. The errors of N-acetyl-L-methionine and L-carnitine determination were 4–12 and 3–11%, respectively. The determination of L-lysine was complicated by its interaction with Ca2+ ions. The error of the group analysis was no greater than 9%. The reverse character of the viral markers’ sorption by the membranes provided long-term sensor operation.

A novel potentiometric multisensory system for the analysis of sulfamethoxazole and trimethoprim combination drugs was developed. The potentiometric sensors (Donnan potential (DP) was used as an analytical signal) with an inner reference solution were based on perfluorosulfonic acid (PFSA) membranes modified with polyaniline (PANI) by in situ oxidative polymerization. The order of the membrane treatment with precursor solutions and their concentrations was varied. Additionally, the PFSA/PANI composite membranes were hydrothermally treated at 120 °C. The influence of the preparation conditions and the composition of membranes on their sorption and transport properties was studied. We estimated the factors affecting the sensitivity of DP-sensors based on the PFSA/PANI composite membranes to ions of sulfamethoxazole and trimethoprim simultaneously presented in solutions. A developed multisensory system provided a simultaneous determination of two analytes in aqueous solutions without preliminary separation, derivatization, or probe treatment. The re-estimation of the calibration characteristics of the multisensory system did not show a statistically significant difference after a year of its use. The limits of detection of sulfamethoxazole and trimethoprim were 1.4 × 10−6 and 8.5 × 10−8 M, while the relative errors of their determination in the combination drug were 4 and 5% (at 5 and 6% relative standard deviation), respectively.

Nafion is a perfluorosulfonic acid polymer that is most commonly used in proton-exchange membrane fuel cells. The processes of pretreatment and formation of such membranes strongly affect their properties. In this work, dispersions of Nafion in various ionic forms and dispersing liquids (ethylene glycol, N,N-dimethylformamide, N-methyl-2-pyrrolidone and isopropyl alcohol–water mixtures in different ratios) were obtained and studied. Membranes fabricated by casting of the various dispersions were also studied. The effect of the nature of the dispersing liquid and the counterion on the properties of Nafion dispersions, the morphology of the polymer in the dispersions and the characteristics of the membranes obtained from them has been shown. Based on the overall results, it can be concluded that the use of perfluorosulfonic acid dispersions in aprotic polar solvents is advisable for obtaining membranes by the casting procedure. This is because it provides optimal polymer morphology in the dispersion, which leads to the formation of films with good selectivity, mechanical and transport properties. The performed investigations show the relationship between the composition of dispersions, the morphology of the polymer and the properties of the membranes formed from them by the casting procedure.

The paper presents the results of a study of water uptake, ionic conductivity, and Donnan potential in systems with perfluorosulfonic acid membranes in the H+, Li+, Na+, and K+ ionic forms and solutions of inorganic electrolytes. The properties of commercial membranes Aquivion E87-05S and Nafion 212, as well as membranes obtained from dispersions of Nafion 212 in solvents of various nature (N,N-dimethylformamide, 1-methyl-2-pyrrolidone, mixtures of isopropyl alcohol with water in a volume ratio of 80–20) have been studied. The effect of the number of functional groups, the length of the side chain of polymer macromolecules, and the morphology of the polymer in membranes on their equilibrium and transport properties depending on the nature of the counterion has been determined. The effect of relaxation and electrophoretic factors on the transfer of alkali metal ions through the system of pores and channels of perfluorosulfonic acid membranes is discussed. The slope of the concentration dependences of the Donnan potential for all highly hydrated membranes in the H+ form has been found to be close to the Nernstian one, while the selectivity to alkali metal ions increases for membranes with the highest ion exchange capacity or the lowest amount of sorbed water and diffusion permeability due to the exclusion of co-ions from the membrane phase.

The degradation of sulfacetamide with the formation of sulfanilamide leads to a deterioration in the quality of pharmaceuticals. In this work, potentiometric sensors for the simultaneous determination of sulfanilamide, sulfacetamide and inorganic ions, and for assessing the degradation of pharmaceuticals were developed. A multisensory approach was used for this purpose. The sensor cross-sensitivity to related analytes was achieved using perfluorosulfonic acid membranes with poly(3,4-ethylenedioxythiophene) or polyaniline as dopants. The composite membranes were prepared by oxidative polymerization and characterized using FTIR and UV-Vis spectroscopy, and SEM. The influence of the preparation procedure and the dopant concentration on the membrane hydrophilicity, ion-exchange capacity, water uptake, and transport properties was investigated. The characteristics of the potentiometric sensors in aqueous solutions containing sulfanilamide, sulfacetamide and alkali metals ions in a wide pH range were established. The introduction of proton-acceptor groups and π-conjugated moieties into the perfluorosulfonic acid membranes increased the sensor sensitivity to organic analytes. The relative errors of sulfacetamide and sulfanilamide determination in the UV-degraded eye drops were 1.2 to 1.4 and 1.7 to 4%, respectively, at relative standard deviation of 6 to 9%.

Perfluorosulfonic acid membranes MF-4SC modified by carbon nanotubes (CNT) with carboxyl and sulfo groups are studied as materials for potentiometric cross-sensitive sensors for the determination of nicotinic acid in pharmaceutical solutions. The effect of the concentration of CNT and proton-donor properties of their surface on the equilibrium and transport properties of membranes and the characteristics of sensors is found. The effect of interfering hydroxonium ions on the response of sensors in nicotinic acid solutions is reduced in using membrane samples containing 0.5 and 1.0 wt % CNT- $${\text{SO}}_{3}^{ - }.$$ For these samples, the limit of detection for nicotinic acid ions in aqueous solutions was 1.0 × 10–5 M, and the relative error and RSD value in determining nicotinic acid in tablets were 0.8–1.3% and 5%, respectively. The best characteristics for the determination of active and auxiliary substances in nicotinic acid injections were achieved using a system of DP-sensors based on membranes containing 1.0 wt % CNT-COO– and 1.5 wt % CNT- $${\text{SO}}_{3}^{ - }.$$ The relative error and RSD in the determination of nicotinic acid in injections were 3 and 0.9%, respectively.

Perfluorosulfonic acid membranes MF-4SC containing 0.5–1.0 wt % carbon nanotubes with carboxyl groups on the surface have been manufactured. On their basis, multisensory systems have been developed for the simultaneous determination of amino acids (the total concentration of their anionic and zwitterionic forms) and K+ cations in aqueous solutions at pH 8–10 in the concentration range from 1.0 × 10–4 to 5.0 × 10–2 M. The relative error in the determination of alanine (5–15%), valine (0.3–10%), and phenylalanine (0.7–5%) is comparable with that for K+ cations (1.4–11%). Differences in the cross sensitivity of sensors based on the pristine and modified membranes, necessary for their use in multisensory systems, are achieved due to changes in the microstructure of membranes and the appearance of new reaction centers that affect the conditions of non-exchange sorption of aliphatic and aromatic amino acids in different ways.

This work provides an overview of the processes of fouling, the deposition of substances on the surface or in the pores of membranes, leading to deterioration of their performance. Degradation and fouling phenomena in various membrane materials, as well as the mechanisms of these processes, are considered. It is shown that, despite the difference in the chemical composition, morphology of membranes, ion exchangers, and the phenomena in which they are used, the phenomena leading to clogging of their surface and pores are largely similar. Among the main substances that contaminate membranes are organic molecules, polyelectrolytes, crystals of inorganic substances formed from ions contained in a solution, as well as colloidal particles, and biological organisms. The binding strength of foulants essentially depends on their nature and on the chemical composition of the membranes. At the same time, many fouling phenomena have their own characteristics. For example, in the processes of electricity generation in fuel cells or hydrogen production in electrolyzers, the formation of oxides or metal particles is observed in the membrane pores due to the electrolysis processes. The consequences of the processes of fouling and methods of their control are also considered. It should be noted that cleaning of membranes is still the main method of preventing fouling. At the same time, in recent years, research has been intensively developed in the field of inhibition of corrosion processes, as well as the creation of integrated approaches that integrate various processing processes, including both membrane and other technologies.

Sulfamethoxazole and trimethoprim are synthetic bacteriostatic drugs. A potentiometric multisensory system for the analysis of sulfamethoxazole and trimethoprim combination drugs was developed. Perfluorosulfonic acid membranes containing functionalized CNTs were used as the sensor materials. The CNTs’ surface was modified by carboxyl, sulfonic acid, or (3-aminopropyl)trimethoxysilanol groups. The influence of the CNT concentration and the properties of their surface, as well as preliminary ultrasonic treatment of the polymer and CNT solution before the casting of hybrid membranes, on their ion-exchange capacity, water uptake, and transport properties was revealed. Cross-sensitivity of the sensors to the analytes was achieved due to ion exchange and hydrophobic interactions with hybrid membranes. An array of cross-sensitive sensors based on the membranes containing 1.0 wt% of CNTs with sulfonic acid or (3-aminopropyl)trimethoxysilanol groups enabled us to provide the simultaneous determination of sulfamethoxazole and trimethoprim in aqueous solutions with a concentration ranging from 1.0 × 10−5 to 1.0 × 10−3 M (pH 4.53–8.31). The detection limits of sulfamethoxazole and trimethoprim were 3.5 × 10−7 and 1.3 × 10−7 M. The relative errors of sulfamethoxazole and trimethoprim determination in the combination drug as compared with the content declared by the manufacturer were 4% (at 6% RSD) and 5% (at 7% RSD).

MF-4SC membranes have been modified by polyaniline (PANI) with the oxidative polymerization method. The influence of the method of obtaining hybrid membranes and the content of PANI in them on the value of IEC, water uptake, and transport properties have been investigated. The characteristics of DP‑sensors (DP is Donnan potential) based on the obtained membranes in aqueous solutions containing saccharin and sodium ions at pH < 7 have been established. It is found that appearance of additional sorption centers in the form of amino groups and fragments with π-π conjugation when introducing PANI to membranes promotes the increase in the sensitivity of DP-sensors to saccharin ions. The use of MF-4SC/PANI membranes obtained by various methods makes it possible to reduce the correlation between the cross-sensitive DP-sensors responses and provides high accuracy of the simultaneous determination of saccharin and sodium ions in aqueous solutions.

Hybrid materials based on MF-4SC perfluorosulfonic acid membranes have been studied as materials of potentiometric sensors for the determination of nicotinic acid in aqueous solutions and pharmaceuticals. The hybrid membranes contained incorporated nanoparticles of zirconia and silica with a sulfonated (directly or via hydrocarbon groups) surface (MF-4SC/ZrO2– $${\text{SO}}_{3}^{ - },$$ MF-4SC/SiO2–(CH2)3– $${\text{SO}}_{3}^{ - }$$ ) and nanoparticles of silica modified with 3-aminopropyl (MF-4SC/SiO2–(CH2)3– $${\text{NH}}_{3}^{ + }$$ ). The relationships between the nature, concentration of dopant, transport properties of materials, and characteristics of sensors based on them have been established. The limits of detection of nicotinic acid ions in the aqueous solutions have been found to be 10–8–10–7 М. The array of cross-sensitive sensors based on membranes containing 5 wt % of SiO2–(СН2)3– $${\text{SO}}_{3}^{ - }$$ and 3 wt % of SiO2–(CH2)3– $${\text{NH}}_{3}^{ + }$$ (15 mol %) has been used to determine the active and auxiliary substances in the nicotinic acid pharmaceutical. The error of nicotinic acid determination in the preparation is 2%.

Местные анестетики прокаина (2-(диэтиламино)этил-4-аминобензоат) и бупивакаина ((RS)-1-Бутил-N-(2,6-диметилфенил)-пиперидин-2-карбоксамид) гидрохлориды широко используют-ся в медицинской практике. Для их определения различными методами используют разнообразные сорбционные материалы. Ранее было показано, что введение поли-3,4-этилендиокситиофена (PEDOT) в перфторированные сульфокатионообменные мембраны Nafion позволяет снизить мешающее влия-ние ионов гидроксония на отклик сенсоров, аналитическим сигналом которых является потенциал Доннана (ПД), в растворах местных анестетиков. При этом модификация оказывает противоположное влияние на чувствительность ПД-сенсоров к катионам прокаина и бупивакаина. В этой связи иссле-дование сорбционных свойств данных материалов в растворах местных анестетиков представляет интерес для дальнейшей оптимизации характеристик сенсоров.Целью работы было исследование сорбции катионов прокаина и бупивакаина из их водных растворов мембранами Nafion-117, модифицированными PEDOT. Показано, что влагосодержание мембран Nafion-117 и Nafion-117+PEDOT, приведенных в равновесие с растворами местных анесте-тиков, снижается из-за присутствия объемных катионов с гидрофобными фрагментами в структуре, при этом замещение протонов на органические катионы ограничено стерическим фактором. Влагосо-держание мембран, приведенных в равновесие с раствором BupHCl, снижается в 1.4-1.8 раз по срав-нению с таковым для образца в Н+-форме, а концентрации сорбированных катионов бупивакаина и десорбированных протонов соизмеримы в пределах погрешности. Влагосодержание мембран, приве-денных в равновесие с раствором ProHCI, снижается в 3.7-4.7 раз по сравнению с исходной, а концен-трация десорбированных ионов гидроксония ниже, чем концентрация сорбированных ионов прокаи-на. Кроме того, возрастание концентрации PEDOT в мембране противоположно влияет на сорбцию прокаина и бупивакаина из водных растворов. Возможной причиной является различное расположе-ние функциональных групп в структуре катионов, в результате которого катионы прокаина склонны к образованию димеров и мицелл в водных растворах, что способствует их сверхэквивалентной сорб-ции, тогда как для катионов бупивакаина это не свойственно.