Sevda Aydar

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.

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.