Isolation of Mn(II), Fe(III), Cu(II) and Ni(II) ions on strongly acidic cation-exchange resins followed by determination of inorganic arsenic by anodic stripping voltammetry

The possibility of ion exchange technique with of IC-H Hypersep cartridge (Metrohm, Switzerland), sulfonated cation-exchange resins KU-2-8 (Russia) and Purolite C100 (UK) has been shown for ion separation of Mn (II), Fe(III), Cu(II) and Ni(II) ions from arsenite and arsenate ions. The conditions for ion-exchange removal of interfering cations in water when determining different arsenic(III, V) by stripping voltammetry have been optimized. The KU-2-8 cation-exchange resin based cartridge was found to be appropriate for use in the proposed sample preparation for water. The developed technique of analysis has been applied for the separated determination of inorganic arsenic forms in waters of different origin by anodic stripping voltammetry. The correctness of experimental results has been confirmed by the standard addition method

Электрохимическое поведение триптофана и 5-гидрокситриптофана на модифицированном многостенными углеродными нанотрубками и полифолиевой кислотой электроде

A possible mechanism for the concentration and oxidation of tryptophan and 5-hydroxytryptophan on an electrode modified with carbon nanotubes and polyfolic acid has been proposed. The influence of the pH of the solution, the accumulation potential, and the potential sweep speed on the analytical signals of amino acids has been investigated. When the pH increases, the potentials of the anode peaks shift to the region of negative values; the I – pH dependence passes through the maximum with the pH of 6.8. Based on the processing of the dependences of the peak current and the peak potential on the potential sweep speed, it has been found that tryptophan and 5-hydroxytryptophan oxidize with the participation of two electrons and two protons. The transfer process of the first electron limits the electrochemical reaction. The process is controlled by diffusion and adsorption. The diffusion coefficients are equal to 9.7.10–6 cm2/s and 7.4.10–6 cm2/s for tryptophan and 5-hydroxytryptophan, the maximum adsorption value for tryptophan has been 1.63.10–10 mol/cm2 and for 5-hydroxytryptophan it has been 6.41.10–1 mol/cm2. The optimal parameters of concentration and oxidation of tryptophan and 5-hydroxytryptophan in the compresence have been established: the pH of 6.8; the accumulation potential of 0.1 V, the electrolysis time of up to 120 s, the optimal scanning velocity of 120 mV/s. The limit of quantification has been 5.10–8 MВ работе предложен возможный механизм концентрирования и окисления триптофана и 5-гидрокситриптофана на электроде, модифицированном углеродными нанотрубками и полифолиевой кислотой. Исследовано влияние рН раствора, потенциала накопления, скорости развертки потенциала на аналитические сигналы аминокислот. При повышении рН потенциалы анодных пиков смещаются в область отрицательных значений, зависимость I – pH проходит через максимум при рН 6,8. На основании обработки зависимостей тока пика и потенциала пика от скорости развертки потенциала установлено, что окисление триптофана и 5-гидрокситриптофана происходит при участии двух электронов и двух протонов. Лимитирует электрохимическую реакцию процесс переноса первого электрона. Процесс контролируется диффузией и адсорбцией. Коэффициенты диффузии равны 9,7.10–6 см2/с и 7,4.10–6 см2/с для триптофана и 5-гидрокситриптофана, величина предельной адсорбции для триптофана составила 1,63.10–10 моль/см2, а для 5-гидрокситриптофана – 6,41.10–11 моль/см2. Установлены оптимальные параметры концентрирования и окисления триптофана и 5-гидрокситриптофана при совместном присутствии: рН 6,8; потенциал накопления –0,1 В, время электролиза до 120 с, оптимальная скорость развертки 120 мв/с. Нижняя граница определяемых концентраций составила 5.10–8

Metal-polymer sensors for voltammetric analysis

The way of the graphite electrodes production, modified by polymeric composition, containing nanoparticles of gold or mercury, for determination of metals’ ions by the method of stripping voltammetry is offered. The influence of copolymer’s structure, nature of solvent, concentration of metal-modifier, viscosity of composition, film’s thickness and conditions of its formation on electrochemical and mechanical characteristics of sensor systems was studied. The approbation of electrodes was carried out using the certified techniques with help of the method of stripping voltammetry during determination of zinc, cadmium, lead, copper, mercury, arsenic, selenium

Metal-polymer sensors for voltammetric analysis

The way of the graphite electrodes production, modified by polymeric composition, containing nanoparticles of gold or mercury, for determination of metals’ ions by the method of stripping voltammetry is offered. The influence of copolymer’s structure, nature of solvent, concentration of metal-modifier, viscosity of composition, film’s thickness and conditions of its formation on electrochemical and mechanical characteristics of sensor systems was studied. The approbation of electrodes was carried out using the certified techniques with help of the method of stripping voltammetry during determination of zinc, cadmium, lead, copper, mercury, arsenic, selenium

Synthesis and thermomechanical properties of hybrid photopolymer films based on the thiol-siloxane and acrylate oligomers

The synthesis of hybrid oligomers for photopolymer compositions was carried out based on the thiol-ene reaction between the tetraacrylate dihydroxydiphenylsulfide derivative and thiol-siloxane oligomer. Thiol-siloxane oligomer was synthesized by condensation of diphenylsilanediol and 3-(mercaptopropyl)-trimethoxysilane. The thiol-siloxane oligomer structure was identified by 1H, 13C, 29Si NMR spectroscopy including COSY, HSQC, and HMBC methods and by MALDI-TOF mass spectrometry. The hybrid oligomers were obtained at different tetraacrylate:thiol-siloxane oligomer ratios (1:2, 1:1, 2:1). The obtained compositions are resistant to the oxygen inhibition of photopolymerization and give flexible, thermostable, and rigid polymer films under UV light at air atmosphere. The degree of the film photopolymerization was monitored by IR spectroscopy. The thermomechanical properties of photopolymer films were determined using thermogravimetric, differential scanning calorimetric, and dynamic mechanical analyses. The storage modulus (E′) at room temperature (1.16–1.88 GPa) and the glass transition temperatures (78–133 °C) were determined for photopolymer films obtained at different ratios of acrylate and thiol-siloxane units. The photocured hybrid films exhibit high stability to thermal decomposition in the inert (T10% over 321 °C) and oxidizing (T10% over 314 °C) atmospheres