A method was developed to fabricate a glassy carbon electrode with electrodeposited palladium particles and a molecularly imprinted polymer derived from nicotinamide. This approach enables the determination of dopamine in the presence of structurally related compounds. The incorporation of a polymer featuring specific recognition sites tailored to the template molecule significantly enhanced the sensitivity and selectivity of dopamine detection. The immobilization of palladium particles on the electrode surface further improved the selectivity of voltammetric dopamine determination, even in the presence of adrenaline and noradrenaline, which exhibited a 200 mV difference in oxidation peak potentials. The analytical signal showed a linear bilogarithmic dependence on dopamine concentration within the range 5.0 × 10–9 to 5.0 × 10–3 M. This method was successfully applied to an analysis of urine samples, demonstrating its practical utility in real-world applications.

Modified electrodes based on gold particles, mixed-valence ruthenium oxides, and a binary system combining these components were developed for the voltammetric determination of ceftriaxone, cefotaxime, and cefoperazone. The electrode with the binary system of gold particles and mixed-valence ruthenium oxides, which exhibited the best performance, was used for the detection of cephalosporins in flow-injection analysis. Optimal conditions for the detection of cephalosporins in a flow-injection system were selected. The dependence of the analytical signal on the concentration of the compounds under consideration is linear on logarithmic coordinates over the range from 5 × 10–7 to 5 × 10–3 M. The proposed procedure was tested in the determination of cephalosporins in pharmaceuticals.

It is found that mixed-valence iridium oxides electrodeposited on the surface of a glassy carbon electrode exhibit catalytic activity in the oxidation of caffeine. In this case, a more pronounced catalytic effect is obtained on an electrode modified with a composite based on a film of a perfluorinated sulfopolymer (Nafion) and mixed-valence iridium oxides. A selective voltammetric method for the determination of caffeine is developed. A linear logarithmic dependence of current on the caffeine concentration is observed in the range from 1 × 10–8 to 5 × 10–3 M. The developed method was used to determine caffeine in energy drinks.

A method of immobilizing Au–Pd binary system on a glassy carbon (GC) electrode surface covered by reduced graphene oxide (GOred) was developed. Using GOred as a matrix for inclusion of Au–Pd binary system resulted in significant increase of its catalytic activity in tetracycline (TC) electro-oxidation process due to increased dispersion of the deposit and formation of nano-sized metal particles (average diameter of particles was around 50 nm). Optimal conditions of immobilizing Au–Pd binary system for achieving maximum electrocatalytic effect were determined. A possibility of amperometric detection of TC on GC modified with Au–Pd and GOred composite (Au–Pd–GOred–GC) by flow injection analysis (FIA) was demonstrated. The method demonstrated high sensitivity (the lowest detection limit of 5 nM), rapidity and efficiency (about 60 samples per hour). The flow injection amperometric method for TC determination hereby developed was tested in analyzing flower honey samples from different Volga Region districts.

Abstract. It was found that mixed valent iridium oxides electrodeposited on the surface of a glass-carbon electrode exhibit catalytic activity in the oxidation of caffeine. A more pronounced catalytic effect was obtained on the electrode modified with a composite based on a film of perfluorinated sulfonated polymer (Nafion) and mixed valent iridium oxides. A selective voltammetric method for the determination of caffeine was developed. A linear logarithmic dependence of current on caffeine concentration was observed in the range from 1×10–8 to 5×10–3 M. The developed method was used in the determination of caffeine in energy drinks.

Electrodes modified with gold particles, multi-walled carbon nanotubes, an ionic liquid based on 1-butyl-3-methylimidazolium hexafluorophosphate, and a composite derived from these materials have been developed for the voltammetric determination of sulfamethazine, sulfacetamide, and sulfathiazole. Cyclic voltammetry reveals that modifying the surface of a glassy carbon electrode with gold particles, a composite of carbon nanotubes, and an ionic liquid increases its effective surface area. Electrochemical impedance data indicate that the rate of electron transfer on the modified electrodes surpasses that on the unmodified ones. The composite electrode containing gold particles, carbon nanotubes, and the ionic liquid, exhibited the best performance, was utilized for the amperometric determination of sulfonamides in a batch-injection analysis system. Optimal parameters for the determination of sulfonamides in the batch-injection setup were found. The relationship between the analytical signal and the concentration of the compounds on the logarithmic coordinates is linear, ranging from 1 × 10–8 to 5 × 10–3 M for sulfamethazine and sulfacetamide, and from 1 × 10–7 to 5 × 10–3 M for sulfathiazole. The proposed method for determining sulfonamides has been tested in ananalysis of pharmaceutical preparations.

An Erratum to this paper has been published: https://doi.org/10.1134/S1061934822380014

The catalytic activity of particles of gold, cobalt, and a gold–cobalt binary system electrodeposited on the surface of planar carbon electrodes was found in the oxidation of glucose in a neutral medium. The amperometric response of a screen-printed electrode modified with a gold–cobalt binary system was used as an analytical signal in the determination of glucose in a sequential injection system. The linear logarithmic dependence of current on the glucose concentration was observed in the range from 5 × 10 –8 to 5 × 10 –2 M. The use of a screen-printed electrode modified with a gold–cobalt binary system as an amperometric detector in a sequential injection system makes it possible to selectively determine glucose in saliva in the concentration range used for medical diagnosis.

The Au–Bi binary system electrodeposited on the surface of a glassy carbon electrode exhibits catalytic activity during the electrooxidation of phenylephrine, paracetamol, and caffeine that enhances the peak currents and decreases overvoltage in the oxidation of organic compounds. The potential difference between the peaks of oxidation on the modified electrode is 400 mV for phenylephrine and paracetamol and 300 mV for phenylephrine and caffeine, respectively. The possibility of simultaneous voltammetric determination of phenylephrine, paracetamol, and caffeine on the glassy carbon electrode modified by the Au–Bi binary system was established. The calibration curve is linear in the concentration range from 5·10–6 to 5·10–3 M. The developed method was tested in the analysis of combined drugs.

A procedure was suggested for voltammetric determination of streptomycin from the catalytic current on a glassy carbon electrode with a composite based on reduced graphene oxide and gold–nickel binary system. The working conditions of the electrode modification (volume of the graphene oxide and chitosan suspension, duration of the electrolytic reduction of immobilized graphene oxide and electrodeposition of the gold–nickel binary system) and the conditions for recording the catalytic current in the flow injection system were determined. The procedure for streptomycin determination in a flow, compared to the determination under stationary conditions, is more sensitive, reproducible, and rapid. The streptomycin detection limit was 0.45 nmol, and the productive capacity of the analysis was 60 samples per hour. The streptomycin determination procedure passed trials in analysis of cow milk.

It was found that oxides of manganese (MnOx), bismuth (ВiOx), gold (AuOx), and ВiOx–MnOx and MnOx–AuOx binary systems electrodeposited on the surface of planar carbon electrodes (SPE) exhibited catalytic activity during electrooxidation of thiamine, riboflavin, pyridoxine and cyanocobalamin in acidic media. Immobilization of the binary systems on the surface of the SPE working electrode allowed to achieve a joint selective voltammetric determination of two-component systems of the vitamins considered: riboflavin and pyridoxine on SPE with BiOx–MnOx (ВiOx–MnOx–SPE) and MnOx–AuOx (MnOx–AuOx–SPE); and riboflavin and thiamine or riboflavin and cyanocobalamin on MnOx–AuOx–SPE. The calibration dependences obtained for the considered vitamins using voltammetry on BiOx–MnOx–SPE and MnOx–AuOx–SPE electrodes were observed in the range from 1×10–6 to 1×10–3 M. Detection limit of thiamine, pyridoxine and cyanocobalamin was decreased by an order of magnitude compare to static conditions in a sequential injection system (SI-system). To implement two- and three-component analysis of biologically active additives (BAA) and drugs in the SI-system, the surface of the working electrode modified with MnOx–AuOx binary system was covered with poly-2-vinylpyridine (PVP) or Nafion (Nf) polymer films. SPE with two working electrodes (DSPE) modifies with MnOx–AuOx were used in the two-component analysis of BAA samples. PVP film was deposited on the electrode for thiamine determination and Nf film was deposited on the electrode for pyridoxine determination. Combination of SPE and DSPE with polymer composites containing MnOx–AuOx binary system and PVP or Nf in a two-detector SI-system made it possible to implement a three-component analysis of drugs containing thiamine, pyridoxine and cyanocobalamin. Excipients present in them did not interfere with the results of the determination. Application of the proposed SI-system scheme increased selectivity, speed and productivity of the analysis to 540 determinations per hour.

The control of the precise concentration of steroid hormones and their synthetic analogs in biomedical objects is a relevant analytical task. A method for selective and highly sensitive simultaneous amperometric determination of adrenaline, melatonin, and cortisol with the use of a two-detector flow-injection system is developed. Screen-printed carbon electrodes (SPE) with one or two working electrodes modified with a gold–palladium binary system that exhibits catalytic activity upon electrooxidation of the organic compounds under consideration are used as detectors. The high sensitivity of determination is attributed to the catalytic properties of the metal modifier: the transition from the metal to the binary system leads to an increase in the catalytic oxidation current of hormones. The selectivity of determination of adrenaline in the presence of melatonin and cortisol is provided by the difference in the oxidation potentials of the hormones on the proposed electrode. For selective determination of melatonin and cortisol, the surface of the modified working electrode is coated with a Nafion film. The difference of potentials of the peaks of oxidation of adrenaline, melatonin, and cortisol on such an electrode is 300 mV. The proposed method is tested in the analysis of urine samples. The flow-injection scheme is supplemented with a dialyzer and a chromatographic minicolumn to eliminate the interfering effect of electrophilic compounds. The linear bilogarithmic dependence of the analytical signal on the concentration of adrenaline, melatonin, and cortisol is observed in the ranges of 5.0 × 10–10–5.0 × 10–3, 5.0 × 10–11–5.0 × 10–3, and 5.0 × 10–12–5.0 × 10–3 mol/L, respectively. Amperometric determination of the hormones in the flow-injection system leads to an increase in the productivity of the analysis and a decrease in the consumption of the sample and makes it possible to automate the process.

5-гидрокситриптофан, пиридоксин и аскорбиновая кислота являются важными биологически активными веществами, без которых невозможно оптимальное функционирование центральной нервной системы и сердечно-­сосудистой системы. Для контроля состава биологически активных добавок в клинической диагностике важно определять их содержание в реальном времени. Установлено, что частицы бинарной системы «золото – ​палладий», осажденные на планарном электроде, проявляют каталитическую активность при электроокислении 5-гидрокситриптофана, пиридоксина и аскорбиновой кислоты. Для селективного проточно-­инжекционного амперометрического определения этих соединений при совместном присутствии применяли двухканальную проточно-­инжекционную схему с параллельным расположением двух детекторов, в качестве которых выступали планарные электроды, модифицированные частицами бинарной системы «золото – ​палладий». Предлагаемый способ определения рассматриваемых органических соединений обеспечивает высокую производительность анализа.

We developed a method for the selective and sensitive voltammetric determination of ascorbic and oxalic acids. A screen-printed electrode, modified by gold–palladium bimetallic system and exhibiting catalytic activity in the electrooxidation of the organic acids under consideration, was used as a detector. The difference between the potentials of oxidation peaks of these compounds was 400–500 mV. The proposed method enables an in situ voltammetric determination of ascorbic and oxalic acids in citrus fruits and orange juices without sample preparation. The results of the voltammetric determination are comparable with the data of iodometry and permanganometry, which are the recommended methods for the analysis of fruit juices.

В настоящее время все больший интерес вызывает разработка вольтамперометрических способов определения широкого круга органических соединений, в том числе биологически активных на ХМЭ на основе неорганических проводящих полимерных пленок, функционирующих на основе принципов электрокатализа.Изучено электроокисление ацикловира (АцВ) и валацикловира (ВАцВ) на электроде с пленкой из полифолиевой кислоты (поли-ФК), нанесенной на стеклоуглеродную (СУ) подложку и на СУ с восстановленным оксидом графена (ГОred-поли-ФК).Композит из ГОredполи-ФК получали в две стадии: сначала капельным методом на поверхность СУ наносили суспензию оксида графена с хитозаном, которую высушивали под ИК-лампой с дальнейшим восстановлением оксида графена до ГОred, после в потенциодинамическом режиме проводили электрополимеризацию пленки из фолиевой

We proposed a method for the selective and highly sensitive amperometric determination of dopamine and adrenaline in the presence of ascorbic and uric acids in a flow-injection system. Screen-printed electrodes modified with palladium nanoparticles, exhibiting catalytic activity in the electrooxidation of catecholamines, were used as a detector. The difference between the oxidation peak potentials of these compounds is 200 mV. A linear bilogarithmic dependence of the analytical signal on the concentration of dopamine and adrenaline is observed in the ranges from 5 × 10 –12 to 5 × 10 –8 M and from 1 × 10 –9 to 1 × 10 –5 M, respectively. For simultaneous two-component analysis, screen-printed electrodes with two working electrodes were used, that is, dual screen-printed electrodes modified with palladium nanoparticles, which enable two substances to be determined simultaneously at two different potentials. The proposed method for the joint flow-injection amperometric determination of dopamine and adrenaline using a modified dual screen-printed electrode was tested in the analysis of urine.

It was found that nickel particles electrodeposited on the surface of planar carbon electrodes (PE; Ni–PE) exhibit catalytic activity in the electrooxidation of glucose, insulin, and cholesterol (CS) in alkaline media, and cobalt particles (Co–PE), in the oxidation of CS, insulin, and uric acid (UA) in neutral media. In recording an analytical signal in a system of sequential-injection analysis with amperometric detection, the bilogarithmic dependence of current on the analyte concentration on a Ni–PE electrode is linear in the range from 5 × 10–6 to 5 × 10–2 M for glucose, from 1 × 10–6 to 1 × 10–4 M for insulin, and from 5 × 10–6 to 5 × 10–3 M for CS. On the Co–PE electrode, it is linear from 5 × 10–7 to 5 × 10–3 M for CS, from 5 × 10–8 to 5 × 10–4 M for insulin, and from 5 × 10–8 to 5 × 10–3 M for UA. It is shown that the use of a two-detector system and modified double planar electrodes ensures the selective determination of the studied biologically active compounds in blood serum.

Кортизол и мелатонин – два гормона, которые прямо влияют на бодрствование и сон. Для контроля нарушений циклов сна / бодрствования, которые могут способствовать развитию раковых опухолей, необходимо определять содержание кортизола и мелатонина в биологических жидкостях. Определено, что частицы золота, осажденные на планарный электрод, проявляют каталитическую активность при электроокислении кортизола и мелатонина, а осажденные частицы палладия, меди и кобальта – только при электроокислении мелатонина. Для одновременного анализа двух веществ при двух различных потенциалах применяли двой­ные планарные электроды, модифицированные частицами золота. Линейная билогарифмическая зависимость аналитического сигнала от концентрации аналита наблюдалась в интервалах от 1 • 10–11 до 1 • 10–5 М для кортизола и от 5 • 10–10 до 5 • 10–3 М для мелатонина. Использование двой­ного планарного электрода, модифицированного частицами золота, для амперометрического определения кортизола и мелатонина в проточно-­инжекционной системе обеспечивает высокую производительность до 360 определений / ч.

A composite film of poly-3,4-ethylenedioxythiophene (PEDOT) with a gold deposit (Au-PEDOT-GCE) on the surface of a glassy carbon electrode (GCE) shows electrocatalytic activity in the oxidation of paracetamol. Working conditions for the immobilization of the Au-PEDOT composite on the GCE were determined. A method for the voltammetric determination of paracetamol on Au-PEDOT-GCE was proposed. It was revealed that the dependence of the oxidation current of paracetamol on its concentration is linear in the range from 1·10 –7 to 1·10 –3 mol·L –1 . The developed voltammetric method was tested to determine paracetamol in drugs.