Asiye Aslıhan Avan

Square-wave stripping voltammetric determination of caffeic acid on electrochemically reduced graphene oxide–Nafion composite film

An electrochemical sensor composed of Nafion-graphene nanocomposite film for the voltammetric determination of caffeic acid (CA) was studied. A Nafion graphene oxide-modified glassy carbon electrode was fabricated by a simple drop-casting method and then graphene oxide was electrochemically reduced over the glassy carbon electrode. The electrochemical analysis method was based on the adsorption of caffeic acid on Nafion/ER-GO/GCE and then the oxidation of CA during the stripping step. The resulting electrode showed an excellent electrocatalytical response to the oxidation of caffeic acid (CA). The electrochemistry of caffeic acid on Nafion/ER-GO modified glassy carbon electrodes (GCEs) were studied by cyclic voltammetry and square-wave adsorption stripping voltammetry (SW-AdSV). At optimized test conditions, the calibration curve for CA showed two linear segments: the first linear segment increased from 0.1 to 1.5 and second linear segment increased up to 10 µM. The detection limit was determined as 9.1×10(-8) mol L(-1) using SW-AdSV. Finally, the proposed method was successfully used to determine CA in white wine samples.

Conducting polymer modified screen-printed carbon electrode coupled with magnetic solid phase microextraction for determination of caffeine

In the current study, we introduce magnetic solid phase microextraction coupled with electrochemical detection of caffeine. A commercially available disposable screen-printed carbon electrodes modified with poly Alizarin Red S are employed as electrochemical sensors in the detection stage. However, the suitability of magnetic solid phase microextraction for electroanalytical methods such as square wave voltammetry has not been declared. With our optimised conditions in hand, the system response was linearly proportional to the concentration of caffeine in the range of 0.5-20µM with a correlation coefficient of about 0.9987. The detection limit of the sensing system was found to be 0.05µM (a signal-to-noise ratio of 3). At the end of the study, the suitability of this new procedure for the analysis of energy drink, soft drink, and chocolate milk samples was demonstrated.

Electrochemical Determination of Brucine in Urine with a Poly(Alizarin Red S)-modified Glassy Carbon Electrode

ABSTRACT A poly(Alizarin Red S)-conducting polymer was prepared on glassy carbon electrodes by multiple scan cyclic voltammetry using 0.1 M Alizarin Red S in pH 7 phosphate buffer. The poly(Alizarin Red S)-modified electrode was used for the direct determination of 2,3-dimethoxystrychnidin-10-one (brucine). The prepared poly(Alizarin Red S) electrodes were characterized by impedance spectroscopy and cyclic voltammetry. The influence of the supporting electrolyte, pH, and scan rate on the brucine current was characterized. The second cycle and the current signal value were selected to be optimum for quantitaive measurements. An irreversible oxidative peak and two pairs of well-defined peaks were obtained at the poly(Alizarin Red S)–glassy carbon electrode. The current from the second scan increased linearly with the concentration of brucine from 30 to 1,000 nM. The limit of detection for brucine was 5.0 × 10−9 M. The developed method was successfully used for the determination of brucine in human urine.

Simultaneous Electrochemical Determination of α-Tocopherol and Retinol in Micellar Media by a Poly(2,2′-(1,4 Phenylenedivinylene)-bis-8-Hydroxyquinaldine)-Multiwalled Carbon Nanotube Modified Electrode

ABSTRACT A novel method was developed for the simultaneous electrochemical determination of α-tocopherol (viatmin E) and retinol (vitamin A) using a poly(2,2′-(1,4-phenylenedivinylene)-bis-8-hydroxyquinaldine)/multiwalled carbon nanotube modified glassy carbon electrode. The simple and rapid voltammetric approach was evaluated for real samples using Triton X-100 to solubilize the analytes in the absence of organic solvent. The calibration graph for α-tocopherol was linear from 8 to 100 µM with a limit of detection of 0.1 µM in the presence of 80 µM retinol. The response was also linear with retinol concentration from 5 to 200 µM with a detection limit of 0.8 µM in the presence of 40 µM α-tocopherol. The developed method was employed for the determination of the vitamins in pharmaceutical products.

Poly(2,2′-(1,4-phenylenedivinylene) Bis-8-hydroxyquinaldine) Modified Glassy Carbon Electrode for the Simultaneous Determination of Paracetamol and p-Aminophenol

A novel assay is reported for the simultaneous determination of paracetamol and p-aminophenol using a poly(2,2′-(1,4-phenylenedivinylene)bis-8-hydroxyquinaldine) modified glassy carbon electrode. Poly(2,2′-(1,4-phenylenedivinylene)bis-8-hydroxyquinoline) modified electrodes were prepared by electrochemical polymerization. The electrode surface was characterized by scanning electron microscopy. The electrochemical behavior of the modified electrode was investigated by cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy. The anodic peak potentials for paracetamol and p-aminophenol were at 580 and 337 millivolts, respectively, with a separation of 243 millivolts, adequate for their simultaneous determination. The results showed that the linear dynamic ranges for paracetamol and p-aminophenol were 0.5–200 micromolar and 3–150 micromolars, whereas the limits of detection were 0.075 and 0.45 micromolar, respectively. The novel poly(2,2′-(1,4-phenylenedivinylene)bis-8-hydroxyquinaldine) modified electrode provided excellent selectivity, sensitivity, and stability and was employed for the determination of paracetamol and p-aminophenol in pharmaceutical products and urine.

Electrochemical Determination of Dopamine Using a Graphene–Screen-Printed Carbon Electrode with Magnetic Solid-Phase Microextraction

ABSTRACT A magnetically separable Fe3O4@Diaion HP-2MG composite was prepared using the coprecipitation method and the resulting magnetic Fe3O4@Diaion HP-2MG composites were used for the separation and preconcentration of trace amounts of dopamine. For the detection stage, square wave voltammetry on a disposable graphene–screen-printed carbon electrode was successfully used for the determination of dopamine. The graphene–screen-printed carbon electrode exhibited excellent electroanalytical performance for dopamine. The linear concentration range was from 0.8 to 80 µM and a detection limit of 50 nM for dopamine was obtained. In combination with the magnetic solid-phase extraction method, the sensor response was linearly proportional to the concentration of dopamine in the range of 0.01–6.0 µM with a correlation coefficient of approximately 0.9992. The detection limit of the sensor was found to be 5.0 nM by square wave voltammetry. The combined methodology was successfully applied to determine dopamine in urine samples with good recoveries ranging from 95 to 98%.

Magnetic solid phase microextraction for determination of caffeine coupled with poly (Alizarin Red) modified screen-printed carbon electrode detection

E technologies have been experiencing a recent renaissance in water treatment. These techniques are used for brackish desalination as well as in industrial applications. Examples of electrochemical separation processes include electrodialysis (ED) and capacitive deionization (CDI) and its advanced version, membrane CDI (MCDI). Very little is reported about the biofouling propensity of electrochemical treatment processes used for natural types of water. Adhered cells are not only likely to decrease the ion capacity of the electrical double layer, electrodes conductivity and transport properties of ion exchange membranes, but also as inactivated or dead cells they might present a beneficial substratum for the undesired attachment and proliferation of approaching planktonic bacteria. Surprisingly, only a few studies in the ED, CDI, and MCDI fields deal with the fundamental aspects of bacteria adherence to the electrodes and the development of biofilms under the influence of the electric fields prevailing in these installations. Most of the studies in this field refer to the problem from a sanitary point of view, preventing device-related infections in hospital environments or disinfecting contaminated liquids. The mechanisms of bacteria inactivation remained however rather speculative in most of the mentioned reports. The present study is focused on the factors governing bio-macromolecule and bacterial adherence and biofilm development on electronically conductive surfaces such as carbon, graphite and gold, as well as on ion exchange membranes, in the absence and the presence of an externally applied electric field. A two-electrode flow cell including one transparent (ITO) electrode for on-line microscopic observations is used for bacterial attachment and biofilm growth studies. The biofouled electrodes are analyzed for biovolume and live/dead bacteria by using confocal laser microscopy (CLSM). Quartz crystal microbalance with dissipation and electrochemical module (E-QCM-D) is used for studying mass and rate of electrosorption of model biomacromolecules and bacteria.Abstract: Oxidoreductase enzymes have been employed for almost 5 decades for energy conversion in the form of biofuel cells. However, most enzymatic biofuel cells in the literature utilize complex biofuels, but only partially oxidize the complex biofuel via the use of a single enzyme (i.e. glucose oxidase or glucose dehydrogenase). This presentation will detail the use of enzyme cascades at bioanodes for deep to complete oxidation of fuels to improve performance. These enzyme cascade will include natural metabolic pathways (i.e. the Krebs cycle), as well as minimal metabolic pathways to promote electron flux. It will also compare fuel options for biofuel cells and discuss the importance of structural orientation of enzymes and enzyme complexation in enzymatic cascades for efficient energy conversion. This enzyme cascades inspired us to consider mitochondria as bioelectrocatalysts as well, so direct mitochondrial bioelectrocatalysis will also be discussed.The electrooxidation of small organic molecules such as formaldehyde, formic acid, methanol, ethanol, ethylene glycol, glycerol, and so on is relevant to interconversion between chemical and electrical energies. Although these have considerably low thermodynamic potentials compared to hydrogen, the oxidation process generally demands high overpotentials because of the ubiquitous formation of surface‐blocking carbonaceous species. The occurrence of parallel pathways and the formation of stable soluble by‐products also contribute to the poor utilization of all electrons involved in the oxidation process. Thecomplex kinetics found in these systems can also result in nonlinear manifestations such as autocatalysis and oscillatory dynamics. Besides the considerable amount of earlier experimental reports, only recently has some understanding of the chemistry underlying the dynamics been achieved. Moreover, a number of interesting and unexpected behaviors have been observed under oscillatory regime. In this chapter, we briefly review the recent advances on the oscillatory electrooxidation of small organic molecules, with emphasis on (a) the general phenomenology, (b) the use ofin situ andonline approaches, (c) the effect of temperature, and (d) the oscillations on modified surfaces. Moreover, some implications of nonlinearities in low temperature fuel cells are also discussed.1 Universidade Federal do Rio de Janeiro, UFRJ Campus-Macaé Professor Aloísio Teixeira, Av. Aluizio da Silva Gomes, 50, Granja dos Cavaleiros, CEP: 27930-560, Macaé, RJ, Brazil. 2 Universidade Federal do Rio de Janeiro, Escola de Química, Departamento de Processos Inorgânicos, Av. Athos da Silveira Ramos, 149, Bloco E, Sl E-206 Ilha do Fundão, CEP: 21941-909, Rio de Janeiro, RJ, Brazil. * E-mail: rodrigosqm@macae.ufrj.brL cell operated with ionic liquid electrolytes is a very promising energy storage technology for electric vehicle and plug-in hybrid electric vehicle due to several favorable characteristics of ionic liquids. However, Li-air cells that employ room temperature ionic liquid (RTIL) electrolytes exhibit poor performance due to limited oxygen solubility and low reactant species mobility. To circumvent these aforementioned drawbacks, we investigated the electrical performance of a Li-air cell with ionic liquid electrolytes operating at high temperature. A continuum based model developed for ternary electrolyte system is used to quantify the performance of the Li-air cell, with an ionic liquid (MPPY-TFSI) electrolyte, as a function of operating temperature. Key parameters of ionic liquid electrolytes are obtained from atomistic simulations, such as molecular dynamics (MD) and density functional theory (DFT) calculations. The continuum based cell level simulation results show that the battery performance can be improved significantly by increasing operating temperature. For instance, specific capacity as high as 3000 mAh/g can be achieved at 110°C operating temperature, which is almost 25 times higher than its counterpart at room temperature. Simulation results also reveal that by increasing the operating temperature, the specific capacity can be improved significantly for high load current density, which is one of the most critical drawbacks in RTIL based Li-air battery. We also studied the effect of cathode thickness on the performance of Li-air battery at different operating temperature. The transport limitation of oxygen and lithium ions can be alleviated at higher operating temperature suggesting that even thicker cathode materials can be used to enhance the cell capacity at elevated temperature.