This work was focused on study of a behaviour of the food additivum butylated hydroxyanisole on modified carbon electrodes by the voltammetric techniques - cyclic and differential pulse voltammetry. Glassy carbon and carbon paste electrode were used. Multiwalled carbon nanotubes (MWCNT) in combination with three different binders (acetonitrile, nafione or chitosane) were employed for the electrode modification. Carbon paste electrode was unable to modificate with film containing carbon nanotubes and acetonitrile, its active surface was treated only with nafione and chitosane film. All three mentioned modifications were applied in case of glassy carbon electrode. Butylated hydroxyanisole provided a significantly higher signal using electrodes modified with carbon nanotubes with all three binders in contrast to electrodes without any surface modification. The glassy carbon electrode with carbon nanotube / acetonitrile film on its surface appeared to be the most effective for analytical purposes. Voltammetric determination of butylated hydroxyanisole using this electrode provided a better defined and higher analytical signal and lower relative standard deviations in comparison with other ways of modification. The limit of detection of butylated hydroxyanisole obtained by cyclic voltammetry on glassy...

Differential pulse voltammetry (DPV) was used for developing a method for the determination of phenothiazine derivatives, namely chlorpromazine (CHP) and levomepromazine (LMP), using a glassy carbon electrode (GCE) and a graphite electrode, both with a 2 mm disc diameter. Comparison of quantification limits (LQ) for both substances on both electrodes was performed. After optimizing and processing the results, the optimal conditions for measuring calibrations were as follows: Britton- Robinson (BR) buffer at pH 4.0. Calibration dependences were measured inthe concentration range from 1·10-7 to 1·10-4 mol·dm-3 . There was no need for electrochemical electrode regeneration or matrix pretreatment. The results showed higher measurement sensitivity for CHP, and the graphite electrode also showed higher sensitivity. Although there were measured lower concentrations with the graphite electrode in comparison to the GCE, because of the low repeatability of the measurements in the lower concentration range 1-10·10-7 mol·dm-3 , the LQ is comparable to the results reached on the GCE. Besides to the BR buffer, measurements in other matrices (drinking water and river water) were also made. The following LQ values were achieved: 1.0·10-6 mol·dm-3 (in BR buffer), 1.1·10-6 -1.4·10-6 mol·dm-3 (in drinking water) and...

Made available in DSpace on 2017-07-20T12:40:14Z (GMT). No. of bitstreams: 1 Giselle Nathaly Calaca.pdf: 4129912 bytes, checksum: 17ad0dde0faa7762fe24c34e6ffcd471 (MD5) Previous issue date: 2015-03-23 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / The development and validation of analytical methods for quantification of two associations, antibiotics: sulfamethoxazole (SMX) and trimethoprim (TMP); and depigmenting agents: kojic acid (AK) and hydroquinone (HQ), using unmodified glassy carbon electrode (ECV) and square wave voltammetry (SWV) are described. For the first association, two well defined irreversible oxidation peaks were obtained at 0.96V (SMX) and 1.12V (TMP) in Britton–Robinson buffer (pH 6.0), characterized by diffusion and adsorptive processes, respectively. SWV parameters were optimized by means of 23 Full Factorial Design, and the best analytical signal, in terms of sensitivity and selectivity is obtained at a=30 mV, f=100 s-1 and ΔES=5mV. Under optimized conditions, SWV measurements showed excellent linear response, from 5.5x10-5 to 3.95x10-4 mol L-1 (R=0.9971) and 1.05x10-5 to 1.04x10-4 mol L-1 (R=0.9974) for SMX and TMP, respectively. The detection and quantification limits were found to be 8.52x10-6 mol L-1 and 2.84x10-5 mol L-1 for SMX; and 9.31x10-7 mol L-1 and 3.10x10-6 mol L-1 for TMP, respectively. The proposed method was successfully applied to the simultaneous determination of these antibiotics in commercial pharmaceutical formulations (tablets, oral suspension and injection), without any sample pretreatment. The obtained results are in good agreement with that obtained by the standard HPLC method at a 95% confidence level. For the second association, the redox peak potentials were completely separated in Mcllvaine buffer solution (pH 8.0), KA exhibits a well-defined irreversible oxidation peak at 0.72V and HQ a quasi-reversible redox peak at 0.08 V and -0.02 V, characterized by adsorptive and diffusional processes, respectively. Under SWV parameters optimized (a= 40 mV, f=40 s-1 and ΔES=1mV) by 23 Full Factorial Design, the calibration curves were obtained in the concentration ranges of 3.5×10-5 to 2.5×10-4 mol L-1 (R= 0.9996) for kojic acid and 1.5×10-5 to 1.6×10-4 mol L-1 (R= 0.9994) for hydroquinone. The detection and quantification limits were found to be 7.84x10-6 mol L-1 and 2.61x10-5 mol L-1 for KA; and 3.71x10-6 mol L-1 and 1.24x10-5 mol L-1 for HQ, respectively. The novel electroanalytical method was validated in terms of specificity, linearity, range, accuracy and precision (repeatability and intermediate precision) and successfully applied to the direct simultaneous determination of these bleaching agents in real samples. / O trabalho descreve o desenvolvimento e a validação de métodos analíticos para quantificação de duas associações, os antibióticos: sulfametoxazol (SMX) e trimetoprima (TMP); e os agentes despigmentantes: ácido kójico (AK) e hidroquinona (HQ), empregando-se eletrodo de carbono vítreo (ECV) não modificado e voltametria de onda quadrada (VOQ). Para a primeira associação, dois picos de oxidação irreversíveis em 0,96V (SMX) e 1,12V (TMP) foram observados em tampão Britton–Robinson (pH 6,0), caracterizados por processos difusional e adsortivo, respectivamente. Os parâmetros instrumentais da VOQ foram otimizados por meio de um planejamento fatorial completo 23, sendo a melhor resposta em termos de sensibilidade e seletividade obtida em a=30 mV, f=100 s-1 e ΔES=5mV. Nas condições otimizadas, foram construídas curvas analíticas nos intervalos de concentração de 5,5x10-5 a 3,95x10-4 mol L-1 (R=0,9971) para SMX e 1,05x10-5 a 1,04x10-4 mol L-1 (R=0,9974) para TMP. Os valores de limites de detecção (LD) e de quantificação (LQ) calculados foram: 8,52x10-6 mol L-1 e 2,84x10-5 mol L-1 para SMX e 9,31x10-7 mol L-1 e 3,10x10-6 mol L-1 para TMP, respectivamente. O método proposto foi aplicado para determinação simultânea dos fármacos em diferentes amostras farmacêuticas (comprimidos, injeção e suspensão oral) sem a necessidade de nenhum tipo de pré-tratamento da amostra. Os resultados obtidos através do método voltamétrico foram comparados aos obtidos pelo método farmacopeico (HPLC) e comprovou-se que não há diferença significativa em um nível de confiança de 95%. Para a segunda associação, nos voltamogramas cíclicos em tampão Mcllvaine (pH=8,0) um pico de oxidação irreversível em +0,7V foi observado para o AK, enquanto que para HQ foi observado um processo quase-reversível, com picos de oxidação em 0,08V e redução em -0,02V, caracterizados por processos adsortivo e difusional, respectivamente. Utilizando-se os parâmetros da VOQ otimizados (a= 40 mV, f= 40 s-1 e ΔES= 1mV), através de um planejamento fatorial completo 23, as curvas de calibração foram obtidas nas faixas de concentração de 3,5×10-5 a 2,5×10-4 mol L-1 (R= 0,9996) para AK e 1,5×10-5 a 1,6×10-4 mol L-1 (R= 0,9994) para HQ. Os limites de detecção e quantificação foram: 7,84x10-6 mol L-1 e 2,61x10-5 mol L-1 para AK; e 3,71x10-6 mol L-1 e 1,24x10-5 mol L-1 para HQ, respectivamente. O método voltamétrico desenvolvido foi validado em termos de especificidade, linearidade, faixa de concentração, exatidão e precisão (repetibilidade e precisão intermediária) e aplicado na determinação simultânea dos agentes despigmentantes em amostras de clareadores.

Nos últimos anos, materiais baseados em grafeno têm atraído grande interesse na área eletroquímica devido às suas excelentes propriedades eletrônicas. Neste trabalho, apresentamos a obtenção de óxido de grafeno reduzido utilizando métodos eletroquímicos. A redução eletroquímica do óxido de grafeno (OG) foi realizada na superfície de um eletrodo de carbono vítreo (ECV) utilizando voltametria cíclica. O óxido de grafeno reduzido eletroquimicamente (OG-RE) foi caracterizado utilizando espectroscopia Raman, microscopia eletrônica de varredura (MEV), microscopia de força atômica (MFA), espectroscopia de fotoelétrons excitados por raios-X (XPS) e espectroscopia de impedância eletroquímica. A relação ID/IG obtida através dos espectros Raman do OG e do OG-RE foram de 0,98 e 1,15, respectivamente, indicando que o processo de redução resultou em uma maior desorganização estrutural. A espectroscopia de fotoelétrons de raios-X mostrou que a proporção entre C e O no OG foi de 45,7% e, que após a redução eletroquímica essa relação diminuiu para 38,5%. O eletrodo modificado com OG-RE foi empregado para quantificação de furosemida (FUR) em amostras farmacêuticas utilizando voltametria de pulso diferencial e análise por injeção em fluxo com detecção amperométrica. Os limites de detecção e quantificação calculados para o método proposto foram de 0,35 e 1,18 µmol L-1, respectivamente. Visando à aplicação em amostras de interesse clínico, fabricou-se um sensor descartável e de baixo custo para a detecção de FUR utilizando papel sulfite pintado com lápis de desenho e ativado por laser de CO2. Os estudos voltamétricos utilizando o [Ru(NH3)6]Cl3 mostraram que o transporte de massa neste dispositivo foi governado por difusão e que o tratamento com laser diminui a resistência a transferência de carga, assim como resultou em um menor problema relacionado ao envenenamento da superfície do eletrodo / In recent years, graphene-based materials have attracted great interest in the area of electrochemistry due to its excellent electronic properties. In this work, we present the production of reduced graphene oxide using electrochemical methods. The electrochemical reduction of graphene oxide (GO) was carried out on the surface of a glassy carbon electrode (GCE) using the cyclic voltammetry technique. Electrochemically reduced graphene oxide (ER-GO) was characterized using Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), Xray excited photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). ID / IG ratio obtained through Raman spectra of GO and ER-GO were 0.98 and 1.15, respectively, indicating that the reduction process resulted in greater structural disorganization. XPS showed that the ratio between C and O in the GO was 45.7% and that after electrochemical reduction this ratio decreased to 38.5%. The ER-GO modified electrode was used as a sensor for furosemide (FUR) in pharmaceutical samples using the techniques of differential pulse voltammetry and flow injection analysis with amperometric detection. The limits of detection and quantification for the proposed method were 0.35 and 1.18 µmol L-1, respectively. Aiming to the application in clinical samples a disposable, low-cost paper-based sensor for the detection of FUR was fabricated using office paper painted with drawing pencil and activated by CO2 laser. Voltammetric studies using [Ru(NH3)6]Cl3 have shown that mass transport in this device was controlled by diffusion and the laser decreases resistance to charge transfer, as well as, avoided the problem with electrode surface poisoning

<p>U okviru ove doktorske disertacije, razvijene su elektroanalitičke metode za određivanje odabranih pesticida primenom hronopotenciometrije. Ispitana je mogućnost primene elektrode od staklastog ugljenika i tankoslojne živine elektrode kao radnih elektroda za određivanje insekticida imidakloprida i herbicida metamitrona i metribuzina. U cilju optimizacije uslova hronopotenciometrijske tehnike, za svaki ispitivani sistem (pesticid/radna elektroda) ispitan je uticaj najznačajnijih eksperimentalnih parametara na analitički signal pesticida, uključujući mehanizam generisanja analitičkog signala na radnoj elektrodi (oksidacija/redukcija), optimalnu metodu za uklanjanje rastvorenog kiseonika iz analiziranog rastvora, kao i vrstu, pH i koncentraciju pomoćnog elektrolita. Nakon toga definisan je optimalni opseg potencijala i struje redukcije. Pored toga, u okviru validacije metode za svaki ispitivani sistem, ispitan je i definisan opseg linearnosti, određena granica detekcije i granica kvantifikacije, ispitana preciznost, tačnost, robusnost i selektivnost metode. Dobijeni analitički signal za ispitivane pesticide bio je posledica ireverzibilne redukcije analita na radnoj elektrodi, a za svaki analit dobijen je jedan redukcioni pik. U slučaju određivanja metribuzina eksperimenti su pokazali da se analitički signal ne može detektovati na elektrodi od staklastog ugljenika uz kori&scaron;ćenje dostupne instrumentacije. Ispitivanja u model-rastvorima za svaki ispitivani sistem pokazala su dobre karakteristike u pogledu preciznosti, tačnosti, selektivnosti i robusnosti metode. Najveća osetljivost za sva tri pesticida postignuta je uz primenu tankoslojne živine elektrode, a vrednosti granice detekcije iznosile su 0,17 mg/l za imidakloprid, 0,07 mg/l za metamitron i 0,04 mg/l za metribuzin. Nakon optimizacije i validacije, razvijene hronopotenciometrijske metode primenjene su na komercijalne formulacije pesticida i uzorke vode. U cilju dodatne potvrde hronopotenciometrijskih rezultata na uzorcima vode izvedena su komparativna merenja uz primenu hromatografske LC-MS/MS analize.</p> / <p>Within this doctoral dissertation, electroanalytical methods for the determination of selected pesticides using chronopotentiometry are developed. The possibility of using glassy carbon electrode and thin film mercury electrode as a working electrode for determination of insecticide imidacloprid and herbicides metamitron and metribuzin is investigated. In order to optimize the conditions of the chronopotentiometric technique for each tested system (pesticide/working electrode), the influence of the most important experimental parameters on the analytical signal of the pesticides is investigated, including the generating mechanism of the analytical signal on the working electrode (oxidation/reduction), the optimal method for removal of dissolved oxygen from the analyzed solution, as well as type, pH, and concentration of the supporting electrolyte. Afterwards, the optimal range of potential and reduction current is defined. Additionally, within the validation of the method for each tested system, the linearity range is determined and defined, limit of detection and quantification are determined, and precision, accuracy, robustness and selectivity of the method are tested. The obtained analytical signal for the investigated pesticides is the result of irreversible reduction of the analyte on the working electrode, and for each analyte one reduction peak is obtained. In the case of metribuzin determination, the experiments have shown that by using the available instrumentation the analytical signal can not be detected on the glassy carbon electrode. Investigation in model solutions for each tested system shows good characteristics in terms of precision, accuracy, selectivity and robustness of the method. The highest sensitivity for all three pesticides was achieved by using thin film mercury electrode, and values of detection limit were 0.17 mg/l for imidacloprid, 0.07 mg/l for metamitron and 0.04 mg/l for metribuzin. After optimization and validation, the developed chronopotentiometric methods are applied to commercial pesticide formulations and water samples. In order to further confirm the chronopotentiometric results on the water samples, comparative measurements are performed using chromatographic LC-MS/MS analysis.</p>

Nos últimos anos, materiais baseados em grafeno têm atraído grande interesse na área eletroquímica devido às suas excelentes propriedades eletrônicas. Neste trabalho, apresentamos a obtenção de óxido de grafeno reduzido utilizando métodos eletroquímicos. A redução eletroquímica do óxido de grafeno (OG) foi realizada na superfície de um eletrodo de carbono vítreo (ECV) utilizando voltametria cíclica. O óxido de grafeno reduzido eletroquimicamente (OG-RE) foi caracterizado utilizando espectroscopia Raman, microscopia eletrônica de varredura (MEV), microscopia de força atômica (MFA), espectroscopia de fotoelétrons excitados por raios-X (XPS) e espectroscopia de impedância eletroquímica. A relação ID/IG obtida através dos espectros Raman do OG e do OG-RE foram de 0,98 e 1,15, respectivamente, indicando que o processo de redução resultou em uma maior desorganização estrutural. A espectroscopia de fotoelétrons de raios-X mostrou que a proporção entre C e O no OG foi de 45,7% e, que após a redução eletroquímica essa relação diminuiu para 38,5%. O eletrodo modificado com OG-RE foi empregado para quantificação de furosemida (FUR) em amostras farmacêuticas utilizando voltametria de pulso diferencial e análise por injeção em fluxo com detecção amperométrica. Os limites de detecção e quantificação calculados para o método proposto foram de 0,35 e 1,18 &#181;mol L-1, respectivamente. Visando à aplicação em amostras de interesse clínico, fabricou-se um sensor descartável e de baixo custo para a detecção de FUR utilizando papel sulfite pintado com lápis de desenho e ativado por laser de CO2. Os estudos voltamétricos utilizando o [Ru(NH3)6]Cl3 mostraram que o transporte de massa neste dispositivo foi governado por difusão e que o tratamento com laser diminui a resistência a transferência de carga, assim como resultou em um menor problema relacionado ao envenenamento da superfície do eletrodo / In recent years, graphene-based materials have attracted great interest in the area of electrochemistry due to its excellent electronic properties. In this work, we present the production of reduced graphene oxide using electrochemical methods. The electrochemical reduction of graphene oxide (GO) was carried out on the surface of a glassy carbon electrode (GCE) using the cyclic voltammetry technique. Electrochemically reduced graphene oxide (ER-GO) was characterized using Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), Xray excited photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). ID / IG ratio obtained through Raman spectra of GO and ER-GO were 0.98 and 1.15, respectively, indicating that the reduction process resulted in greater structural disorganization. XPS showed that the ratio between C and O in the GO was 45.7% and that after electrochemical reduction this ratio decreased to 38.5%. The ER-GO modified electrode was used as a sensor for furosemide (FUR) in pharmaceutical samples using the techniques of differential pulse voltammetry and flow injection analysis with amperometric detection. The limits of detection and quantification for the proposed method were 0.35 and 1.18 &#181;mol L-1, respectively. Aiming to the application in clinical samples a disposable, low-cost paper-based sensor for the detection of FUR was fabricated using office paper painted with drawing pencil and activated by CO2 laser. Voltammetric studies using [Ru(NH3)6]Cl3 have shown that mass transport in this device was controlled by diffusion and the laser decreases resistance to charge transfer, as well as, avoided the problem with electrode surface poisoning

Philosophiae Doctor - PhD (Chemistry) / Tuberculosis (TB) is an airborne disease caused by Mycobacterium tuberculosis (MTB) that usually affects the lungs leading to severe coughing, fever and chest pains. It was estimated that over 9.6 million people worldwide developed TB and 1.5 million died from the infectious disease of which 12 % were co-infected with human immunodeficiency virus (HIV) in the year 2015. In 2016 the statistics increased to a total of 1.7 million people reportedly died from TB with an estimated 10.4 million new cases of TB diagnosed worldwide. The development of the efficient point-of-care systems that are ultra-sensitive, cheap and readily available is essential in order to address and control the spread of the tuberculosis (TB) disease and multidrugresistant tuberculosis.

Philosophiae Doctor - PhD / A novel monomer (N,N'-Bis-(1H-pyrrol-2-ylmethylene)-benzene-1,2-diamine-BPPD) was derived from the condensation reaction between o-phenylenediamine and a pyrrole derivative. The monomer was polymerized electrochemically to produce the new polymer material - polymerized(N,N'-Bis-(1H-pyrrol-2-ylmethylene)-benzene-1,2-diamine) PBPPD. This novel polymer material was deposited at the surface of a screen-printed carbon electrode, as a thin film, in the development of chemical sensors for the detection of polycyclic aromatic hydrocarbons (PAHs). The monomer material was characterized in terms of its optical (spectroscopy) and thermal properties. The polymer material was characterized in terms of its surface morphology and its redox electrochemistry. Fourier transform infrared spectroscopy (FTIR) was used to confirm the azomethine bond formation during the condensation reaction of an aldehyde and primary amine derivative. / 2020-08-31

Main goal of this Ph.D. thesis is to develop voltammetric methods for the electrochemical study of novel antimycobacterial compounds hydroxynaphthalene- carboxamides. Firstly, this study was focused on the miniaturization of voltammetric methods and construction of an electrochemical microcell due to usually small volume of samples that are associated with an analysis of biologically active compounds in biological matrices. Therefore, all aspects of the voltammetric procedure were studied in a relation to miniaturization. Microcells were based on commercially available electrodes: glassy carbon electrode as a reliable electrode material with well-described characteristics and a novel silver solid amalgam electrode. This study was carried out with analytes 4-nitrophenol, pesticide difenzoquat, and 1-hydroxy-N-(4-nitrophenyl)naphthalene-2-carboxamide. Attention was paid especially to the optimization of oxygen removal procedures in the drop of a solution. Developed miniaturized methods had the same parameters for the determination of studied compounds as in bigger volumes. The proposed electrochemical microcell can be generally used for voltammetric analysis of those samples of biological or environmental origin that are usually available in very limited volumes. Second part of the thesis was focused...

The object of the study was the pharmaceutical substance TRIAZID of the newest Russian antiviral drug azolo-azinovogo series containing nitro group. Objective: development and validation of the methodology for voltammetric determination of triazide in the pharmaceutical substance TRIAZID on a glassy carbon electrode. Analysis of literature data showed that in the case of biologically active nitro compounds, the most useful for quantitative determination is the electroreduction signal of the nitro group. The advantages of the signal include both the large amount of current generated per mole of the electroactive connection and the relatively low energy requirement for the reduction of the nitro group. This makes it possible to obtain a high current / concentration ratio at low recovery potentials. The conditions for obtaining an analytical signal of triazide on a glassy carbon electrode are optimized. A simple and expressive method for eliminating the interfering effect of dissolved oxygen with the help of sodium sulphite is proposed. / Объектом исследования служила фармацевтическая субстанция ТРИАЗИД новейшего российского противовирусного препарата азоло-азинового ряда, содержащего нитрогруппу. Цель работы: разработка и валидация методики вольтамперометрического определения триазида в фармацевтической субстанции ТРИАЗИД на стеклоуглеродном электроде. Анализ литературных данных показал, что в случае биологически активных нитросоединений наиболее полезным для количественного определения является сигнал электровосстановления нитрогруппы. К преимуществам сигнала можно отнести как большое количество тока, вырабатываемое на моль электроактивного соединения, так и относительно низкую потребность в энергии для восстановления нитрогруппы. Это позволяет получать высокое отношение ток / концентрация при низких потенциалах восстановления. Оптимизированы условия получения аналитического сигнала триазида на стеклоуглеродном электроде. Предложен простой и экспрессный способ устранения мешающего влияния растворенного кислорода с помощью сульфита натрия. Разработана и валидирована по актуальным требованиям Государственной Фармакопеи РФ XIII издания вольтамперометрическая методика определения триазида в фармацевтической субстанции ТРИАЗИД. Контроль содержания триазида по разработанной методике удовлетворяет заявленным критериям приемлемости, не требует дорогостоящего оборудования, привлечения высококвалифицированного персонала, отличается коротким временем анализа. При условии включения в фармстатью предприятия разработанный метод может применяться испытательными лабораториями предприятия в процессе производства препарата.