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.

Biosensor devices that include hybrid nanostructures as transducer surface modifiers meet current requirements for methods of research and determination of drugs, including antidepressants. Here, we consider the features of amperometric monoamine oxidase biosensors based on screen-printed graphite electrodes modified with nanocomposite consisting of C60/cobalt nanoparticles/amino derivative of a second-generation polyether polyol/chitosan in the determination of the tricyclic antidepressant amitriptyline. The best modifier was selected using transmission electron microscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and differential pulse voltammetry. In the biosensor development, the conditions for applying the composite based on cobalt nanoparticles/amino derivative of polyether polyol to the electrode surface were varied: electrochemical deposition, sequential deposition by the layer-on-layer method, and deposition of a mixture. As an analytical signal of the biosensor, we used the peak of the electrochemical oxidation of hydrogen peroxide, which is formed during the enzymatic oxidation of serotonin under the action of monoamine oxidase. The operating principle of the biosensor is based on the inhibitory effect of amitriptyline on the catalytic activity of immobilized monoamine oxidase. For the selected modifier, the determined concentration range of amitriptyline is 1 × 10–4–1 × 10–8 mol/L and the lower limit of the determined contents is 5 × 10–9 mol/L under optimal operating conditions. Comparison of the results of the amitriptyline determination in a pharmaceutical preparation and urine that were obtained using a monoamine oxidase biosensor and the method of fluorescence polarization immunoassay (dilution of the tracer of 1 : 32, dilution of antibodies of 1 : 128, range of working concentrations from 5 × 10–8 to 5 × 10–9 mol/L), which has proven itself in the determination of medicinal substances, confirmed the correctness of the developed method.

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.

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.

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

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 method of amperometric determination of uric acid ( UA ), creatinine ( Cr ) and cholesterol ( CHO ) on planar carbon electrodes ( PE ) modified by gold particles in a flow-injection system has been developed. PE with immobilized gold particles ( Au-PE ) is catalytically active with respect to UA, Cr and CHO. A multiple current increase at modifier oxidation potentials and an oxidation potential decrease of the organic compound as compared to the unmodified electrode during their electrooxidation on Au-PE was observed. The effect of the electrochemical and hydrodynamic parameters of the flow-injection system on the analytical signal was estimated for each compound. The working conditions (applied potential and flow rate) for the maximum analytical signal registration at the modified electrode for the studied biologically active compounds ( BAC ) were selected. With the joint presence of the considered BAC, the dependence graphs of the current on the analyte concentration in logarithmic units were linear in the range from 5x10 -9 to 5x10 -3 mol/l for UA, from 5x10 -7 to 5x 0 -3 mol/l for Cr and from 5x10 -8 to 5x10 -3 mol/l for CHO. Using the two-detector flow system and double planar electrodes ( DPE ) modified with gold particles ( Au-DPE ) allowed the simultaneous determination of the considered BAC. The proposed method was used to determine UA, Cr and CHO in the urine. Keywords: electrooxidation of uric acid, creatinine and cholesterol, modified planar electrode, gold particles, amperometric determination, flow-injection analysis DOI: http://dx.doi.org/10.15826/analitika.2019.23.3.005 (Russian) L. G. Shaidarova, I.A. Chelnokova, I.A. Abzalova, A.V. Gedmina, G.K. Budnikov Kazan (Volga region) Federal University (KFU), ul. Kremlyovskaya, 18, Kazan, 420008, Russia Federation

A method of amperometric determination of uric acid ( UA ), creatinine ( Cr ) and cholesterol ( CHO ) on planar carbon electrodes ( PE ) modified by gold particles in a flow-injection system has been developed. PE with immobilized gold particles ( Au-PE ) is catalytically active with respect to UA, Cr and CHO. A multiple current increase at modifier oxidation potentials and an oxidation potential decrease of the organic compound as compared to the unmodified electrode during their electrooxidation on Au-PE was observed. The effect of the electrochemical and hydrodynamic parameters of the flow-injection system on the analytical signal was estimated for each compound. The working conditions (applied potential and flow rate) for the maximum analytical signal registration at the modified electrode for the studied biologically active compounds ( BAC ) were selected. With the joint presence of the considered BAC, the dependence graphs of the current on the analyte concentration in logarithmic units were linear in the range from 5x10 -9 to 5x10 -3 mol/l for UA, from 5x10 -7 to 5x 0 -3 mol/l for Cr and from 5x10 -8 to 5x10 -3 mol/l for CHO. Using the two-detector flow system and double planar electrodes ( DPE ) modified with gold particles ( Au-DPE ) allowed the simultaneous determination of the considered BAC. The proposed method was used to determine UA, Cr and CHO in the urine. Keywords: electrooxidation of uric acid, creatinine and cholesterol, modified planar electrode, gold particles, amperometric determination, flow-injection analysis DOI: http://dx.doi.org/10.15826/analitika.2019.23.3.005 (Russian) L. G. Shaidarova, I.A. Chelnokova, I.A. Abzalova, A.V. Gedmina, G.K. Budnikov Kazan (Volga region) Federal University (KFU), ul. Kremlyovskaya, 18, Kazan, 420008, Russia Federation

An inorganic film of ruthenium hexachloroplatinate (RuPtCl6) deposited on the surface of a glassy-carbon electrode exhibited catalytic activity for oxidation of S-containing amino acids. Catalytic electrochemical oxidation of cysteine, cystine, and methionine occurred at various potentials. The optimum conditions for producing a RuPtCl6 film that gave the greatest catalytic effect were found. A method for selective voltammetric determination of cysteine, methionine, and cystine at an RuPtCl6-film electrode was developed. The lower limit of quantitation of cysteine and cystine was 5 × 10–6 M; of methionine, 5 × 10–7 M. The proposed voltammetric method was used to determine cysteine, cystine, and methionine in drugs and vitamin complexes.