Papers by Eduardo Richter
Microchemical Journal, 2020
detection of 3,4methylenedioxymethamphetamine (ecstasy) using a boron-doped diamond electrode wit... more detection of 3,4methylenedioxymethamphetamine (ecstasy) using a boron-doped diamond electrode with differential pulse voltammetry: Simple and fast screening method for application in forensic analysis,
Microchemical Journal, 2017
This work demonstrates the sensitive amperometric determination of omeprazole on screen-printed e... more This work demonstrates the sensitive amperometric determination of omeprazole on screen-printed electrodes (SPE) using batch-injection analysis (BIA). A SPE containing a multiwalled carbon nanotube modified electrode coupled to the BIA system provided an analytical method with a low detection limit (9 nmol L-1), high precision (1.3%) and sample throughput (120 h-1), employing microliter sample volumes injected by an electronic micropipette. The full analytical system presents portable characteristics that enable application for on-site analysis. Analytical results for pharmaceutical samples analyzed by the proposed method were in agreement with those obtained by spectrophotometry. Moreover, the BIA method presented advantages over the flowinjection analysis with amperometric detection such as detection limit, sensitivity, and sample throughput.
Carbon nanotube/reduced graphene oxide thin-film nanocomposite formed at liquid-liquid interface: Characterization and potential electroanalytical applications
Sensors and Actuators B: Chemical, 2018
Abstract This paper presents a new route to produce carbon nanotube/reduced graphene oxide (CNT/r... more Abstract This paper presents a new route to produce carbon nanotube/reduced graphene oxide (CNT/rGO) nanocomposites using the interfacial method to produce high-performance electroanalytical sensing. The nanocomposite thin-film is formed at the cyclohexane/water immiscible interface after stirring of a mixture of CNT and rGO in the biphasic solution and can be transferred to any planar substrate. As a proof-of-concept, the nanocomposite film was transferred to a boron-doped diamond electrode, which was compared with glassy-carbon and gold substrates. Improved electrochemical sensing of model phenolic compounds (dopamine and catechol) under stationary (cyclic voltammetry) and flow (amperometry) conditions was verified in comparison with unmodified and modified surfaces with rGO and CNT using the same method. Electrochemical impedance spectroscopy and heterogeneous electron transfer rate constant (k0) values also evidenced the faster electron transfer for a redox probe on the nanocomposite surface, while the increase in electroactive area by CNT/rGO was minimal in comparison with CNT or rGO (6–12%). Scanning electron microscopic images show the interaction of rGO with CNT and Raman spectra revealed the defect density. Amperometric detection of phenolic compounds showed synergistic properties of CNT and rGO on the response of nanocomposite, which resulted in highly sensitive sensors with superior performance in comparison with electrochemical sensors based on CNT or rGO already reported (nanomolar detection limits for dopamine and catechol). Dopamine determination in serum samples was demonstrated. Hence, this new protocol offers great promises to develop improved electrochemical sensors for a wide range of analytes.
Microchemical Journal, 2015
This work reports a fast and efficient ultrasound-assisted extraction of mercury in inorganic fer... more This work reports a fast and efficient ultrasound-assisted extraction of mercury in inorganic fertilizers for its determination by cold vapor atomic absorption spectrometry (CV AAS) and microwave-induced plasma optical emission spectrometry (MIP OES), using a 10% (w/v) SnCl 2 as reductant agent. A multi-mode sample introduction system (MSIS) was coupled to the MIP OES equipment to make possible the generation of mercury vapor in the nebulizer chamber. The optimized protocol involved the treatment of 150 mg of fertilizer with 4 mL of 30% (v/v) HCl inside glass tubes using a conventional ultrasonic bath for 5 min. Comparable analytical results were obtained for mercury determined by both CV AAS and MIP OES, with better detection limits for the latter technique. The proposed extraction procedure is simple and versatile, and contributes to minimal generation of waste (low volume of diluted HCl) in comparison to the official method.
Química Nova, 2007
THE USE OF PRESSURE GENERATED BY A WATER COLUMN TO CONTROL FLOW RATES IN FLOW ANALYSIS SYSTEMS. T... more THE USE OF PRESSURE GENERATED BY A WATER COLUMN TO CONTROL FLOW RATES IN FLOW ANALYSIS SYSTEMS. This work presents a new approach to control the flow rate in hydrodynamic flow experiments. The combination of air pressure generated by an aquarium air pump and the pressure generated by a water column were used for this purpose. This device supports a stable flow rate without pulsation for a long period of time. Furthermore, the flow rate can be easily controlled at various values in one or more streams. The performance of this approach was investigated using Fe(CN) 6 4solutions in flowing systems using amperometric and voltammetric detection in wall-jet configuration. The results showed that the performance of the proposed device was better than a commercial peristaltic pump. It suggests that this approach can be used successfully in flow analysis systems.
Química Nova, 2013
FAST DETERMINATION OF HYDROQUINONE BY BATCH INJECTION ANALYSIS (BIA) WITH AMPEROMETRIC DETECTION.... more FAST DETERMINATION OF HYDROQUINONE BY BATCH INJECTION ANALYSIS (BIA) WITH AMPEROMETRIC DETECTION. A fast analytical method for determination of hydroquinone in pharmaceutical formulations employing batch injection analysis (BIA) with amperometric detection using a boron-doped diamond electrode is described. The supporting electrolyte was a 0.1 mol L-1 H 2 SO 4 solution (the single reagent used for analysis). The method showed good repeatability (RSD of 0.45%, n=20), wide linear range (from 10 to 2000 µmol L-1 , R=0.9999), low detection limit (0.016 µmol L-1) and satisfactory recovery values (91-96%). Accuracy of the method was evaluated by comparative analyses using high-performance liquid-chromatography. The ability to replace the electronic pipette by disposable syringes (injection procedure) in BIA systems was also shown.
Journal of the Brazilian Chemical Society, 2013
A oxidação electroquímica de clorexidina é investigada pela primeira vez e sua determinação amper... more A oxidação electroquímica de clorexidina é investigada pela primeira vez e sua determinação amperométrica usando um sistema de análise por injeção em fluxo (FIA) é demonstrada. Um pico de oxidação bem definido foi observado próximo de 1,3 V em uma solução 0,1 mol L-1 de HClO 4 em eletrodo de carbono vítreo. O mecanismo da oxidação eletroquímica de clorexidina é dependente do pH e envolve a transferência de um único elétron, possivelmente através da formação de cátion radical. Os parâmetros do sistema FIA foram otimizados e um limite de detecção de 0,3 µmol L-1 foi obtido. O método proposto foi aplicado em enxaguantes bucais e desinfetantes de pele e comparados com cromatografia líquida de alta eficiência. The electrochemical oxidation of chlorhexidine is investigated for the first time and its amperometric determination using a flow-injection analysis (FIA) system is demonstrated. An oxidation peak was observed at around 1.3 V in a 0.1 mol L-1 HClO 4 solution at a glassy-carbon electrode. The mechanism of the electrochemical oxidation of chlorhexidine is pH-dependent and involves a single-electron transfer possibly via radical cation formation. The FIA parameters were optimized and a detection limit of 0.3 µmol L-1 was obtained. The proposed method was applied in mouth rinses and skin disinfectants samples and compared with high-performance liquid chromatography.
Journal of the Brazilian Chemical Society, 2014
Neste trabalho apresentamos um método de eletroforese capilar simples e de baixo custo para deter... more Neste trabalho apresentamos um método de eletroforese capilar simples e de baixo custo para determinação ultra-rápida de princípios ativos presentes em três formulações farmacêuticas diferentes: (i) escopolamina (SCO) e dipirona (DIP); (ii) orfenadrina (ORP), cafeína (CAF) e DIP; (iii) mepiramina (MEP), CAF, DIP e ácido ascórbico (AA). O método proposto é baseado em eletroforese capilar com detecção condutométrica sem contato (CE-C 4 D). As amostras podem ser analisadas em uma única corrida (≤ 1 minuto) usando 10 mmol L-1 de 3,4-dimetoxicinamato e 12 mmol L-1 de trietanolamina como eletrólito de corrida (pH = 8,5). Uma resposta linear (r ≥ 0,993
Journal of the Brazilian Chemical Society, 2008
Este trabalho apresenta uma técnica alternativa de microfabricação para construção de microcélula... more Este trabalho apresenta uma técnica alternativa de microfabricação para construção de microcélulas eletroquímicas descartáveis contendo os eletrodos de trabalho, auxiliar e de referência em um único dispositivo. Trata-se de um processo simples no qual a termo-transferência de máscaras de toner sobre superfícies de ouro obtidas a partir de discos compactos graváveis (CD-R) definem o formato dos eletrodos (contornos). Numa etapa seguinte, o formato é manualmente coberto com tinta usando uma caneta de retroprojetor. A superfície de ouro não protegida pela tinta é convenientemente removida (corrosão química) e a tinta, por sua vez, é facilmente removida com etanol gerando superfícies de ouro sem contaminação. A área final e reprodutível dos eletrodos é definida pela termo-transferência de uma segunda máscara de toner. O eletrodo de referência é obtido por meio de uma deposição manual de cola de prata sobre uma banda de ouro. As microcélulas foram eletroquimicamente caracterizadas usando as técnicas de voltametria cíclica, voltametria linear e voltametria de onda quadrada e várias espécies eletroativas como sistemas modelo. A reprodutibilidade de área dos eletrodos para diferentes microcélulas foi estudada e um desvio-padrão relativo melhor do que 1,0% foi obtido. As microcélulas descartáveis foram usadas com sucesso para a análise de amostras em volumes menores que 200 µL demonstrando boa estabilidade e reprodutibilidade (RSD menor que 2,0%). Essas microcélulas também foram avaliadas para a quantificação de paracetamol e dipirona em formulações farmacêuticas. An alternative technique for the fabrication of disposable electrochemical microcells containing working, reference and auxiliary electrodes on a single device is reported. The procedure is based on thermal-transfer of toner masks onto CD-R (recordable compact discs) gold surfaces to define the layout of the electrodes (contour). In a subsequent step, the layout is manually painted with a permanent marker pen. The unprotected gold surface is conveniently etched (chemical corrosion) and the ink is then easily removed with ethanol, generating gold surfaces without contamination. The final and reproducible area of the electrodes is defined by heat transference of a second toner mask. Silver epoxy is deposited on one of the gold bands which is the satisfactorily used as reference electrode. These microcells were electrochemically characterized by cyclic, linear, and square wave voltammetry, and several electroactive species were used as model systems. The area reproducibility of the electrodes for different microcells was studied and a relative standard deviation better than 1,0% (n = 10) was obtained. Disposable electrochemical microcells were successfully used in analysis of liquid samples with volumes lower than 200 µL and good stability and reproducibility (RSD less than 2.0%) were achieved. These microcells were also evaluated for quantification of paracetamol and dipyrone in pharmaceutical formulations.
Journal of the Brazilian Chemical Society, 2004
O controle do conteúdo de íons inorgânicos em combustíveis veiculares tem uma importante função n... more O controle do conteúdo de íons inorgânicos em combustíveis veiculares tem uma importante função na manutenção do motor. Um método novo e versátil para análise rápida de íons em etanol é apresentado. Eletroforese capilar foi utilizada para quantificar cátions (sódio, potássio, cálcio, magnésio e amônio) e ânions (sulfato, cloreto e nitrato). A injeção direta da amostra no capilar apresentou falta de repetibilidade nos resultados. A evaporação prévia do etanol, seguida pela resuspensão do material residual, levou a resultados confiáveis. Os limites de detecção para os oito íons estiveram na faixa de 0,06 a 0,18 mg L-1. Limites de detecção inferiores podem ser obtidos com o aumento do tempo de injeção e/ou da pressão de injeção. The control of the content of inorganic ions in vehicular fuels plays an important role in the engine maintenance. A novel and versatile methodology to carry out rapid analysis of ions in ethanol is presented. Capillary electrophoresis was used to quantify cations (sodium, potassium, calcium, magnesium, and ammonium) and anions (sulfate, chloride, and nitrate). The injection of the sample directly in the capillary shows some lack of repeatability of the results. The prior evaporation of the ethanol, followed by a re-suspension of the residual material, leads to reliable results. The detection limits of the eight ions range between 0.06 and 0.18 mg L-1. Lower detection limits could be attained by increasing the injection time and/or the injection pressure.
Journal of the Brazilian Chemical Society, 2009
Este trabalho descreve a construção e caracterização de uma célula eletroquímica microfluídica co... more Este trabalho descreve a construção e caracterização de uma célula eletroquímica microfluídica com a inserção dos três eletrodos (trabalho, pseudo-referência e auxiliar) em microcanais com espessuras menores que 20 µm. Os microcanais foram construídos entre duas bases de policarbonato com o uso de uma ou mais máscaras de toner sobrepostas como espaçador. Esta estratégia permite a construção de microcélulas com um volume interno sobre o eletrodo de trabalho entre 0,6 a 2,4 µL. Três diferentes materiais foram otimizados como eletrodos nas microcélulas: filmes de ouro ou compósito de grafite como eletrodo de trabalho, compósito de prata como pseudo-referência e compósito de grafite como eletrodo auxiliar. O desempenho das células microfluídicas foi avaliado usando as técnicas de voltametria cíclica, redissolução potenciométrica a corrente constante e voltametria de redissolução anódica por onda quadrada empregando ferrocianeto e alguns metais pesados (Cu 2+ , Hg 2+ , Pb 2+ , e Cd 2+) como analitos modelo. This work describes the construction and characterization of an electrochemical flow-through microcell with the three electrodes (working, pseudo-reference, and auxiliary) inserted in microchannels with thickness smaller than 20 µm. These microchannels were constructed between two stacked polycarbonate slides using one or more overlapped toner masks as spacer. This strategy allows the construction of microcells with a variable internal volume on the working electrode (0.6 to 2.4 µL). Three different materials were optimized as electrodes: gold film or graphiteepoxy composite as working electrode, silver-epoxy composite as pseudo-reference electrode and, graphite-epoxy composite as auxiliary electrode. The performance of the microfluidic cell was characterized by cyclic voltammetry, potentiometric stripping analysis at constant current, and square wave anodic stripping voltammetry using ferrocyanide and heavy metals (Cu 2+ , Hg 2+ , Pb 2+ , and Cd 2+) as model analytes.
Journal of the Brazilian Chemical Society, 2012
Um método eletroanalítico original e rápido para a determinação de naproxeno em formulações farma... more Um método eletroanalítico original e rápido para a determinação de naproxeno em formulações farmacêuticas usando análise por injeção em batelada (BIA) com detecção amperométrica pulsada é descrito. Eletrodo de carbono vítreo foi usado como eletrodo de trabalho e solução tampão fosfato 0,05 mol L-1 como eletrólito suporte. O método amperométrico envolveu a aplicação contínua de dois pulsos de potencial ao eletrodo de trabalho com intuito de detectar naproxeno pela sua oxidação eletroquímica (+1,5 V por 200 ms) e de limpar a superfície do eletrodo de produtos de adsorção (+1,0 V por 100 ms), evitando contaminação do eletrodo. O método proposto possui várias vantagens para análises de rotina, incluindo: baixo desvio padrão relativo (3,0%, n = 10), elevada frequência analítica (90 h-1), exatidão satisfatória (baseado em determinações comparativas por espectrofluorimetria) e baixo limite de detecção (0,3 µmol L-1). A novel and fast electroanalytical method for naproxen determination in pharmaceutical formulations using batch injection analysis (BIA) with pulsed amperometric detection is described. Bare glassy carbon electrode was used as working electrode and 0.05 mol L-1 phosphate buffer solution as supporting electrolyte. The amperometric method involved the continuous application of two sequential potential pulses to the working electrode in order to detect naproxen by its electrochemical oxidation (+1.5 V for 200 ms) and to clean the electrode surface from adsorption products (+1.0 V for 100 ms), avoiding electrode contamination. The proposed method has several advantages for routine analysis, including: a low relative standard deviation between injections (3.0%, n = 10), high analytical frequency (90 h-1), satisfactory accuracy (based on comparative determinations by spectrofluorimetry) and low limit of detection (0.3 µmol L-1).
Journal of the Brazilian Chemical Society, 2011
Neste trabalho, o desenvolvimento de um método limpo de preparo de amostras para a análise de fer... more Neste trabalho, o desenvolvimento de um método limpo de preparo de amostras para a análise de fertilizantes inorgânicos baseado em extração assistida por ultrassom usando um banho de ultrassom é descrito. Amostras (70 mg) foram sonicadas por 5 min na presença de 2 mL de HNO 3 50% (v/v) dentro de tubos de vidro. A determinação de cobre, chumbo e cádmio nos extratos foi realizada empregando espectrometria de absorção atômica com chama (FAAS). É também demonstrada a possibilidade de empregar um agitador vortex como fonte de agitação mecânica para realizar a extração dos metais. O método proposto usando banho de ultrassom ou agitador vortex é simples, versátil e minimiza a geração de resíduos devido ao emprego de volumes reduzidos de ácido e amostra, contribuindo para o desenvolvimento de um método analítico limpo. In this work, the development of a "green" sample preparation procedure for the analysis of inorganic fertilizers based on ultrasound-assisted extraction using an ultrasonic bath is described. Samples (70 mg) were sonicated for 5 min in the presence of 2 mL of 50% (v/v) HNO 3 inside glass tubes. The determination of copper, lead and cadmium in the extracts were carried out by flame atomic absorption spectrometry (FAAS). It is also demonstrated the possibility of using of a vortex shaker as a mechanical agitation source to perform the metal extraction. The proposed extraction procedure using an ultrasonic bath or a vortex shaker is simple and versatile, and minimizes waste generation due to the employment of reduced volumes of acid and sample, contributing for the development of a clean analytical method.
ELECTROPHORESIS, 2004
Electrophoresis microchip fabricated by a direct-printing process with end-channel amperometric d... more Electrophoresis microchip fabricated by a direct-printing process with end-channel amperometric detection We describe the development of an electrophoresis microchip fabricated by a directprinting process, based on lamination of printed polyester films with end-channel amperometric detection. The channel structures are defined by polyester (base and cover) and by a toner layer (walls). The polyester-toner devices presented an electroosmotic flow (EOF) magnitude of ,10 25 cm 2 V 21 s 21 , which is generated by a polymeric mixture of the toner and polyester composition. The microelectrodes used for detection were produced combining this laser-printer technology to compact discs. The performance of this device was evaluated by amperometric detection of iodide and ascorbate. The detection limits found were 500 nmol?L 21 (135 amol) and 1.8 mmol?L 21 (486 amol) for iodide and ascorbate, respectively.
ELECTROPHORESIS, 2004
Disposable twin gold electrodes for amperometric detection in capillary electrophoresis We descri... more Disposable twin gold electrodes for amperometric detection in capillary electrophoresis We describe a simple and easy way to construct gold microelectrodes for amperometric detection in capillary electrophoresis (CE). The gold microelectrodes, in single or twin sets, were obtained from recordable compact discs (gold-sputtered type), which present highly reproducible surface characteristics. The performance of these electrodes was evaluated by using a home-made CE equipment. The basic steps for the electrode construction are: drawing on a microcomputer; laser printing of the design on wax paper; heat-transfer of the toner onto the gold surface of a peeled recordable compact disc (CD-R); etching of the gold layer from unprinted regions; removal of the toner with a solvent; sealing of unused electrode areas with varnish. One electrode at a time was connected to a potentiostat (or two, to a bipotentiostat) and operated in a wall jet configuration relative to the CE capillary outlet. The amperometric signals were integrated for quantification purposes. Repetitive injections (n = 10) of a mixture containing iodide, ascorbic acid, dipyrone, and acetaminophen (20, 200, 500, and 100 mM), presented relative standard deviations of 2.9, 4.5, 6.1, and 4.0%, respectively. For these analytes, the detection limits (S/N = 3, 30 s of 100 mm hydrodynamic injection) were 0.1, 0.5, 3.1, and 1.1 mM, respectively.
Disposable Gold Electrodes with Reproducible Area Using Recordable CDs and Toner Masks
Electroanalysis, 2006
ABSTRACT The fabrication and characterization of very cheap disposable gold disk electrodes with ... more ABSTRACT The fabrication and characterization of very cheap disposable gold disk electrodes with reproducible area is reported. The innovation of the proposed procedure is the use of toner masks to define reproducible areas on uniform gold surfaces obtained from recordable compact disks (CD-R). Toner masks are drawn in a laser printer and heat transferred to gold surfaces, defining exactly the electrodes area. The electrochemical behavior of these disposable electrodes was investigated by cyclic voltammetry in Fe(CN)64− solutions. The relative standard deviation for signals obtained from 10 different gold electrodes was below 1 %. The size of the disk electrodes can be easily controlled, as attested by voltammetric responses recorded by using electrodes with radii varying from 0.5 to 3.0 mm. The advantages of using this kind of electrode for analytical measurements of substances that strongly adsorb on the electrode surface such as cysteine are also addressed.
Electroanalysis, 2005
This paper proposes a simple methodology for mercury quantification in natural water by stripping... more This paper proposes a simple methodology for mercury quantification in natural water by stripping chronopotentiometry at constant current, using gold (film) electrodes constructed from recordable CDs in stationary cell. The proposed method allows the direct measurement of labile mercury in natural waters. To quantify total mercury, a robust and low cost UV irradiation system was developed for the degradation of organic constituents of water. The proposed system presents such advantages as excellent sensitivity, low cost, versatility, and smaller dimensions (portability for on-field applications) when compared with other techniques (ICP, GFAAS, fluorimetry) traditionally utilized for mercury quantification. A large linear region of responses was observed, situated over the range 0.02-200 mg L À1. Various experimental parameters were optimized and the system allowed quantifications in natural samples, with detection limit of 8 ng L À1 and excellent reproducibility (RSD of 1.4% for 48 repetitive measurements using a 10 mg L À1 mercury solution). Different metal ions were evaluated, including copper, as possible interferences on stripping mercury signals. Applications of the new method were demonstrated for the analysis of certified and groundwater samples spiked with a known amount of mercury and for the quantification of methylmercury in synthetic oceanic water, originally utilized for fishes contamination experiment.
Journal of the Brazilian Chemical Society, 2014
Este trabalho reporta a determinação simultânea de paracetamol e naproxeno usando a detecção ampe... more Este trabalho reporta a determinação simultânea de paracetamol e naproxeno usando a detecção amperométrica de múltiplos pulsos em um eletrodo impresso modificado com nanotubos de carbono de parades múltiplas (MWCNT-SPE) adaptado em uma célula de análise em fluxo (FIA) construída em laboratório. Uma sequência de dois pulsos de potencial (+0,30 e 0,70 V por 70 ms cada) foi aplicada continuamente de tal forma que paracetamol foi selectivamente oxidado em +0,30 V e ambos compostos (paracetamol e naproxeno) são oxidados em +0,70 V. Subtração da corrente depois de usar um fator de correção foi empregada para a determinação de naproxeno sem a interferência do paracetamol. O método FIA proposto apresenta alta seletividade e sensibilidade, exatidão adequada (resultados em concordância com cromatografia líquida de alta eficiência), elevada frequência analítica (90 h-1) e baixo custo uma vez que um único SPE pode ser usado durante todo o dia de trabalho adaptado em uma célula em fluxo. This work reports the simultaneous determination of paracetamol and naproxen using multiple-pulse amperometric detection on a multi-walled carbon nanotube modified screenprinted electrode (MWCNT-SPE) adapted in a homemade flow-injection analysis (FIA) cell. A sequence of two potential pulses (+0.30 and +0.70 V for 70 ms each) was applied continuously in such a way that paracetamol is selectively oxidized at +0.30 V and both compounds (paracetamol and naproxen) are oxidized at +0.70 V. Current subtraction after using a correction factor was employed for determination of naproxen without the interference of paracetamol. The proposed FIA method presents high selectivity and sensitivity, adequate accuracy (results in agreement with high-performance liquid chromatography), elevated analytical frequency (90 h-1), and low-cost once a single SPE strip can be used during the whole working day adapted in a flow-cell.
Portable amperometric method for selective determination of caffeine in samples with the presence of interfering electroactive chemical species
Journal of Electroanalytical Chemistry
Uploads
Papers by Eduardo Richter