Browsing by Author "Keskin, Ertugrul"

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Adsorptive Stripping Voltammetric Determination of Higenamine on a Boron-Doped Diamond Electrode Improved by the Use of an Anionic Surfactant
(Elsevier Science Sa, 2020) Allahverdiyeva, Shabnam; Pinar, Pinar Talay; Keskin, Ertugrul; Yunusoglu, Oruc; Yardim, Yavuz; Senturk, Zuhre
The present work describes the first electroanalytical investigation and a new voltammetric method for a cheap, rapid and simple determination of higenamine at a surface of mildly-oxidized boron-doped diamond electrode (at +1.6 V during 180 s). The oxidation of compound was strongly dependent on pH. The sensitivity of method was significantly improved in the presence of anionic surfactant, sodium dodecyl sulfate (SDS). The first oxidation peak was chosen for the electroanalytical determination of higenamine due to its higher sensitivity compared to the other two ones. By employing square-wave stripping mode, there was a linear dependence of the oxidation peak current at +0.75 V and higenamine concentration in the range of 0.5-30.0 mg L-1 (1.84 x 10(-6)-1.11 x 10(-4) M), with a detection limit of 0.13 mg L-1 (4.79 x 10(-7) M) in BR buffer pH 2.0 containing 2 x 10(-4) M SDS (after 30 s accumulation at open-circuit condition). As an example, the practical applicability of the proposed method was tested with the quantification of higenamine in the commercial dietary supplement formulations, with results in good agreement to those obtained declared by high-performance liquid chromatography with diode-array detection as a reference method.
Determination of 7,12-Dimethylbenz[a]anthracene in Orally Treated Rats by High-Performance Liquid Chromatography and Transfer Stripping Voltammetry
(Bentham Science Publ Ltd, 2012) Yardim, Yavuz; Levent, Abdulkadir; Ekin, Suat; Keskin, Ertugrul; Oto, Gokhan; Senturk, Zuhre
A number of polycyclic aromatic hydrocarbons (PAHs) have been shown to be toxicants, and induce carcinogenic and immunotoxic effects. As a model PAH agent, 7,12-dimethylbenz[a]anthracene (DMBA) was the strongest one tested in terms of its biological activities and biotransformation. A new and simple high-performance liquid chromatographic (HPLC) method with diode-array detection at 290 nm was developed and validated for monitoring of DMBA in different matrices (serum, liver and kidney) of rats orally treated with DMBA. Furthermore, the applicability of adsorptive transfer stripping voltammetry (AdTSV) on the pencil-lead graphite electrode to these samples was illustrated using our previously reported data for bulk aqueous solutions of DMBA. HPLC and AdTSV methods, which were compatible with each other, allowed DMBA to be detected down to the levels of 3.82x10(-9) M (0.98 ppb) and 6.73x10(-9) M (1.73 ppb), respectively. Olive oil solutions of DMBA in dose 50 mg/kg were orally administered. 60 days after a single dose of DMBA, its concentrations in these biological samples from rats were measured by means of both methods. Because of rapid biotransformation, DMBA could not be detected in serum. Only low levels of the compounds were deposited unchanged in kidney whereas its levels were considerably higher in liver. These methods were also applied to the assay whether there is an influence of the intake of aqueous extracts of Hypericum Perforatum L. plant on the parent DMBA levels accumulated in rat tissues.
Determination of Tramadol in Pharmaceutical Forms and Urine Samples Using a Boron-Doped Diamond Electrode
(Serbian Chemical Soc, 2020) Keskin, Ertugrul; Allahverdiyeva, Shabnam; Seyho, Esma; Yardim, Yavuz
The present work describes the electroanalytical investigation and a novel voltammetric method for the cheap, fast and simple quantification of tramadol (TRH) using a boron-doped diamond electrode. TRH displayed one well-defined, irreversible and adsorption-controlled oxidation peak at about 1.58 V (vs. Ag/AgCl) in Britton-Robinson buffer (BR, 0.1 mol L-1, pH 3.0) using the cyclic voltammetry technique. The voltammetric responses of the oxidation peaks are dependent on pH and their sensitivity was significantly enhanced in the presence of surfactant media (sodium dodecyl sulphate, SDS). Under the optimized experiment conditions, employing the square-wave stripping mode, it was found that there was an excellent correlation between oxidation peak current and the TRH concentration in the range 0.25 to 50.0 mu g mL(-1) (8.34 x 10(-7)-1.67 x 10(-4) mol L-1), with a detection limit of 0.072 mu g mL(-1) (2.40 x 10(-7) mol L-1) in 0.1 mol L-1 BR buffer (pH 3.0) solution comprising 8 x 10(-4) mol L-1 SDS at 1.52 V (after 30 s accumulation at open-circuit conditions). The developed approach could be used for the quantification of TRH in pharmaceutical formulations and spiked human urine samples with acceptable recoveries.
Electroanalytical Investigation and Determination of Hepatitis C Antiviral Drug Ledipasvir at a Non-Modified Boron-Doped Diamond Electrode
(Elsevier Science Sa, 2020) Allahverdiyeva, Shabnam; Keskin, Ertugrul; Pinar, Pinar Talay; Yunusoglu, Oruc; Yardim, Yavuz; Senturk, Zuhre
This study is about the use of the boron-doped diamond electrode pretreated electrochemically (anodic and subsequent cathodic) in the voltammetric determination of hepatitis C antiviral drug ledipasvir. Cyclic voltammetric measurements revealed that the compound yielded two well-separated irreversible oxidation peaks (P-A1 and P-A2) in acidic medium. The dependence of intensities of currents and potentials on electrode pretreatment, pH and nature of the supporting electrolyte, and other variables was investigated by square-wave voltammetry. Determination of ledipasvir was performed in Britton-Robinson buffer (pH 2.0) on the basis of both P-A1 and P-A2, which offered linear concentration ranges 0.5-60.0 mu g mL(-1) (5.6 x 10(-7)-6.8 x 10(-5) mol L-1) and 5.0-60.0 mu g mL(-1) (5.6 x 10(-6)-6.8 x 10(-5) mol L-1), respectively, with detection limits of 0.12 mu g mL(-1) (1.4 x 10(-7) mol L-1) and 0.76 mu g mL(-1) (8.6 x 10(-7) mol L-1). The practical applicability of developed methodology was tested by the assay of a fixed-dose combination tablet with sofosbuvir.
Electrochemical Determination of Flavonoid Fisetin in Commercial Dietary Supplements Using a Boron-Doped Diamond Electrode
(Wiley-v C H verlag Gmbh, 2023) Allahverdiyeva, Shabnam; Keskin, Ertugrul; Yoruk, Ibrahim; Yardim, Yavuz
For the first time, a boron-doped diamond electrode was utilized to quantitatively determine flavonoid fisetin (FST). Cyclic voltammetric studies have shown that the electrochemical oxidation of FST is irreversible and well-separated two peaks (P-A1 and P-A2) in 0.1 MHNO3 solution. The effects of electrode pretreatment, solution pH, nature of the supporting electrolyte, and instrumental variables on the peak current and potentials of the FST were investigated by square-wave voltammetry (SWV) and then optimum ones were determined. It was observed that the cathodically pre-treated BDD (CPT-BDD) electrode's performance was better than the other pre-treatment procedures for increasing the FST oxidation signal. Under optimized conditions and using the SWV technique, the response of the first anodic peak (P-A1) of the FST was proportional in a concentration range of 0.5-20.0 mu g mL(-1) (1.7x10(-6)-6.9x10(-5) mol L-1) with a detection limit of 0.08 mu gm L-1 (2.8 x 10(-7) mol L-1). Also, it was successfully demonstrated that the proposed method is applicable in commercial nutritional supplement formulations.
Electrochemical Determination of Fluoroquinolone Antibiotic Norfloxacin in the Presence of Anionic Surfactant Using the Anodically Pretreated Boron-Doped Diamond Electrode
(Wiley-v C H verlag Gmbh, 2020) Karahan, Fatih; Basi, Zehra; Keskin, Ertugrul; Pinar, Pinar Talay; Yardim, Yavuz; Senturk, Zuhre
In this article, a simple, fast and inexpensive methodology has been developed for the determination of fluoroquinolone class antibiotic norfloxacin (NFX) in anionic surfactant media (sodium dodecyl sulphate, SDS) using an anodically pretreated boron-doped diamond (APT-BDD) electrode. Cyclic voltammetric studies showed that the NFX gave an irreversible and adsorption controlled anodic oxidation signal at a potential of about +1.32 V on the APT-BDD electrode. The effects of parameters such as the electrode pre-treatment procedure, SDS concentration, and instrumental variables on the electrochemical sensitivity of NFX were evaluated. Under optimized conditions, the linearity was achieved in the range of 0.05 to 4.0 mu g mL(-1) (1.57x10(-7)-1.25x10(-5) mol L-1), with a detection limit of 0.013 mu g mL(-1) (4.07x10(-8) mol L-1) by using square-wave adsorptive stripping voltammetry (SW-AdSV). The feasibility of the developed approach for the quantification of NFX in urine samples was tested.
Electrochemical Determination of Norepinephrine by Adsorptive Stripping Voltammetry Using a Bare Boron-Doped Diamond Electrode
(Editura Acad Romane, 2019) Keskin, Ertugrul; Yardim, Yavuz; Levent, Abdulkadir; Senturk, Zuhre
A boron-doped diamond electrode was used for the first time for sensitive and selective analysis of norepinephrine (NE) using square wave voltammetry (SWV) technique. NE displayed one welldefined, irreversible and adsorption-controlled oxidation peak at about +0.85 V (vs. Ag/AgCl) in Britton-Robinson buffer (BR, 0.1 M, pH 2.0) using cyclic voltammetry (CV) technique. The effect of supporting electrolyte, solution pH and instrumental variables on oxidation peak current were optimized. In optimal experiment conditions, it was found that there was an excellent correlation between oxidation peak current and NE concentration in the range of 1 to 100 mu g mL(-1) (4.9X10(-6) M-4.9 x10(-4) M) with a detection limit of 0.254 mu g mL(-1) (1.2X10(-6) M) in 0.1 M BR buffer (pH 2.0) solution employing square-wave stripping mode. The developed technique can be used for the quantification of NE in the pharmaceutical formulation with acceptable recoveries.
Electrooxidation of Thiourea and Its Square-Wave Voltammetric Determination Using Pencil Graphite Electrode
(Walter de Gruyter Gmbh, 2011) Levent, Abdulkadir; Keskin, Ertugrul; Yardim, Yavuz; Senturk, Zuhre
The electrochemical properties of thiourea (TU) were investigated in pH range 2.0-12.0 by cyclic and square-wave voltammetry. The compound was irreversibly oxidized at a pencil graphite electrode in one or two oxidation steps which are pH-dependent. Based on the voltammetric peak for the second oxidation process of TU in phosphate buffer at pH 12.0, a square-wave voltammetric method was proposed for the determination of the compound in the range 6.3-30 mu m, with a detection limit of 1.29 mu m. The applicability to direct assays of wastewaters was also tested.
First Electroanalytical Investigation and Simple Quantification of a Thrombopoietin-Receptor Agonist Drug Eltrombopag in the Presence of Cationic Surfactant at a Non-Modified Boron-Doped Diamond Electrode
(Elsevier Science Sa, 2020) Allahverdiyeva, Shabnam; Calisir, Meryem; Keskin, Ertugrul; Yardim, Yavuz; Senturk, Zuhre
The present study describes the first electroanalytical investigation and the development of a novel voltammetric method for a sensitive, simple, fast, cheap and eco-friendly determination of eltrombopag (ELT). At a borondoped diamond electrode pretreated electrochemically (anodic and subsequent cathodic), the compound presented one or two oxidation steps at relatively low positive potentials within the pH range 6.0-12.0 by employing square-wave voltammetry. The sensitivity of the measurements was significantly enhanced with the positive effect of cetyltrimethylammonium bromide (CTAB) under the accumulation condition. In Britton-Robinson buffer pH 12.0 containing 2 x 10(-4) mol L-1 CTAB (after 30 s accumulation at open-circuit condition), there was a linear dependence of peak current at +0.19 V (vs. Ag/AgCl) and ELT concentration in the range of 0.1-12.5 mu g mL(-1) (2.3 x 10(-7)-2.8 x 10(-5) mol L-1) with a detection limit of 0.0125 mu g mL(-1) (5.7 x 10(-8) mol L-1). The developed approach could be used for ELT determination in commercial tablet formulations.
First Electroanalytical Methodology for the Determination of Hordenine in Dietary Supplements Using a Boron-Doped Diamond Electrode
(Wiley-v C H verlag Gmbh, 2019) Allahverdiyeva, Shabnam; Keskin, Ertugrul; Pinar, Pinar Talay; Yardim, Yavuz; Senturk, Zuhre
The present work describes the first electrochemical investigation and a simple, rapid and modification-free electroanalytical methodology for quantification of hordenine (a potent phenylethylamine alkaloid) using a boron-doped diamond electrode. At optimized square-wave voltammetric parameters, the observed oxidation peak current in 0.1 M HClO4 at +1.33 V (vs. Ag/AgCl) increased linearly from 5.0 to 100 mu g mL(-1) (3.0x10(-5)-6.1x10(-4) M), with detection limit of 1.3 mu g mL(-1) (7.8x10(-6) M). The applicability of the developed method was tested with the determination of hordenine in the commercial dietary supplement formulations.
First Voltammetric Procedure for Sensing Synthetic Thyroid Hormone Liothyronine Sodium in Tablet Dosage Form Using Anionic Surfactant Media at a Boron-Doped Diamond Electrode
(Elsevier Science Sa, 2025) Ozok, Hande Izem; Keskin, Ertugrul; Yardim, Yavuz
In this study, the voltammetric sensing of liothyronine sodium (LT3Na) was assessed using a boron-doped diamond (BDD) electrode, which had undergone electrochemical pretreatment to improve its surface activity. Cyclic voltammograms of LT3Na revealed well-defined, single, irreversible behavior that is governed by a dual mechanism of adsorption and diffusion at around +1.16 V (vs. Ag/AgCl) in 0.1 mol L- 1 H2SO4 solution. The oxidation peaks of LT3Na were studied using various electrolyte solutions, including Britton-Robinson buffer (0.04 mol L- 1, pH 2-10), phosphate buffer (0.1 mol L- 1, pH 2.5 and 7.4), acetate buffer (0.1 mol L- 1, pH 4.7), and 0.1 mol L- 1 solutions of HNO3, H2SO4, and HClO4, by square wave adsorption stripping voltammetry. The results showed that the oxidation peaks of LT3Na were pH-dependent across the range of 5.0 to 9.0; however, the optimal peak was observed in the H2SO4 solution. Introducing a sodium dodecyl sulfate (anionic surfactant, SDS) into the working electrolyte enhanced the anodic peak currents of LT3Na. A linear correlation for the quantification of LT3Na was obtained at +1.05 V in a 0.1 mol L- 1 H2SO4 solution containing 4 x 10-4 mol L- 1 SDS, under optimized conditions (vs. Ag/AgCl) (using open-circuit condition in 30 s accumulation step). The linear range spanned from 0.5 to 30.0 mu g mL-1 (7.4 x 10- 7-4.5 x 10-5 mol L- 1), with a detection limit of 0.15 mu g mL-1 (2.2 x 10-7mol L- 1). The LT3Na concentration in the drug formulation was successfully quantized using this method. According to our knowledge, this is the initial study to present an electrochemical analysis of this compound.
Simple and Rapid Voltammetric Determination of Cephalosporin Drug Cefixime on Boron-Doped Diamond Electrode
(Springer Wien, 2019) Keskin, Ertugrul; Allahverdiyeva, Shabnam; Seker, Hamza; Yardim, Yavuz
A boron-doped diamond electrode was used for the first time in sensitive and selective analysis of cefixime, a third-generation cephalosporin drug, using the square-wave voltammetry technique. The effect of the pretreatment procedure on the current response at the electrode was investigated. The best signals were obtained by polishing the electrode with a polishing pad after applying anodic and cathodic electrochemical pretreatment to the electrode. Cefixime gave a well-defined, irreversible and diffusion-controlled oxidation peak in 0.1 mol dm(-3) H2SO4 support electrolyte at + 1.25 V (vs. Ag/AgCl 3 mol dm(-3) NaCl). Under the best instrumental conditions and with the pretreatment procedure, a calibration curve was obtained with linearity between 2.2x10(-6) mol dm(-3) and 1.3x10(-4) mol dm(-3) at 5.9x10(-7) mol dm(-3) detection limit. The effect of possible interference substances on the current response for cefixime was investigated and the method was found to have sufficient selectivity. The developed method was successfully applied for the analysis of cefixime from pharmaceutical formulations. The method can be an alternative to the other analytical approaches due to its speed, simplicity, low cost, wide calibration range, and repeatable responses. [GRAPHICS] .
Voltammetric Behavior of Benzo[A]pyrene at Boron-Doped Diamond Electrode: a Study of Its Determination by Adsorptive Transfer Stripping Voltammetry Based on the Enhancement Effect of Anionic Surfactant, Sodium Dodecylsulfate
(Elsevier, 2011) Yardim, Yavuz; Levent, Abdulkadir; Keskin, Ertugrul; Senturk, Zuhre
Benzo[a]pyrene (BaP), a member of the polycyclic aromatic hydrocarbon (PAH) class, is one of the most potent PAH carcinogens. The electrochemical oxidation of BaP was first studied by cyclic voltammetry at the boron-doped diamond electrode in non-aqueous solvent (dimethylsulphoxide with lithium perchlorate). The compound was irreversibly oxidized in a single step at high positive potential, resulting in the well-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure in aqueous and aqueous/surfactant solutions over the pH range of 2.0-8.0. The technique in aqueous solutions had little value in practice because of too small oxidation peak current. This problem was solved when surfactants were added into the sample solution, by which the oxidation peak currents of BaP were found enhanced dramatically. The employed surfactants were sodium dodecylsulfate (anionic, SDS), cetyltrimethylammonium bromide (cationic, CTAB) and Tween 80 (nonionic). Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 2.0 containing 2.5 x 10(-4) M SDS at +1.07 V (vs. Ag/AgCl) (after 120 s accumulation at +0.10 V). The process could be used to determine BaP in the concentration range of 16-200 nM (4.04-50.46 ng mL(-1)), with a detection limit of 2.86 nM (0.72 ng mL(-1)). This method was also applied to determine BaP in model water sample prepared by adding its different concentrations into tap water. (C) 2011 Elsevier B.V. All rights reserved.
Voltammetric Determination of Mixtures of Caffeine and Chlorogenic Acid in Beverage Samples Using a Boron-Doped Diamond Electrode
(Elsevier, 2013) Yardim, Yavuz; Keskin, Ertugrul; Senturk, Zuhre
Herein, a boron-doped diamond (BDD) electrode that is anodically pretreated was used for the simultaneous determination of caffeine (CAF) and chlorogenic acid (CGA) by cyclic and adsorptive stripping voltammety. The dependence of peak current and potential on pH, scan rate, accumulation parameters and other experimental variables were studied. By using square-wave stripping mode after 60 s accumulation under open-circuit voltage, the BDD electrode was able to separate the oxidation peak potentials of CAF and CGA present in binary mixtures by about 0.4 V in Britton-Robinson buffer at pH 1.0. The limits of detection were 0.107 mu g mL(-1) (5.51 x 10(-7) M) for CAF, and 0.448 mu g mL(-1) (1.26 x 10(-6) M) for CGA. The practical applicability of this methodology was tested in commercially available beverage samples. (C) 2013 Elsevier B.V. All rights reserved.
Voltammetric Quantification of a Nonsteroidal Anti-Inflammatory Agent Diflunisal Based on the Enhancement Effect of Cationic Surfactant on Boron-Doped Diamond Electrode
(Soc Chemists Technologists Madeconia, 2021) Keskin, Ertugrul; Allahverdiyeva, Shabnam; Alali, Amer; Yardim, Yavuz
The present work describes a simple, fast and inexpensive voltammetric method for diflunisal measurement using a non-modified boron-doped diamond (BDD) electrode. The oxidation of the agent was irreversible and was a diffusion-controlled process. The sensitivity of the square wave voltammetric measurements were significantly improved when the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was present in the supporting electrolyte solution. Using the square-wave mode, a linear response was obtained for diflunisal quantification in a 0.1 mol l(-1) phosphate buffer solution (pH 2.5) containing 5.10(-5) mol l(-1) CTAB at +1.07 V (vs. Ag/AgCl) (after 30 s accumulation under open-circuit conditions). Linearity was found for 0.05 to 2.0 mu g ml(-1) (2.0.10(-7) - 8.0.10(-6) mol l(-1)) with a detection limit of 0.013 mu g ml(-1) (5.2.10(-8) mol l(-1)). The developed approach could be used for the quantification of diflunisal in pharmaceutical formulations.
Voltammetric Quantification of the Anesthetic Drug Propofol (2,6-Diisopropylphenol) in Pharmaceutical Formulations on a Boron-Doped Diamond Electrode
(Serbian Chemical Soc, 2021) Keskin, Ertugrul; Allahverdiyeva, Shabnam; Ozok, Hande Izem; Yunusoglu, Oruc; Yardim, Yavuz
In this paper, the detailed electrochemistry of propofol (PRO), which is one of the intravenous agents commonly used for sedative-hypnotic purposes, was examined. In cyclic voltammetry, the agent showed one irreversible and diffusion-controlled oxidation peak, resulting in the formation of a couple with a reduction and re-oxidation wave at less positive potentials. The effect of electrode pretreatment procedures on the electrochemical response of PRO was investigated using square wave voltammetry (SWV) and the optimum procedure was used to improve the signal response in subsequent studies. Quantification of PRO was realized based on the first oxidation peak using SWV. After optimization of all variables, the linear working range of PRO was found to be between 2.5 mu g mL(-1) (1.4x 10 s mol L-1) and 160.0 mu g mL(-1) (1.1x 10(-3) mol L-1 , n = 15) with a detection limit 0.71 mu g mL(-1) (3.9 x 1 0(-6) mol L-1). No noteworthy interference effect was detected. Furthermore, the developed method was used for quantification of PRO in pharmaceutical samples.
Voltammetry of Benzo[A]pyrene in Aqueous and Nonaqueous Media: Adsorptive Stripping Voltammetric Determination at Pencil Graphite Electrode
(Wiley-v C H verlag Gmbh, 2010) Keskin, Ertugrul; Yardim, Yavuz; Senturk, Zuhre
A detailed study of the electrochemical oxidation of Benzo[a]pyrene (BaP) at the glassy carbon and pencil graphite electrodes was carried out in aqueous and nonaqueous media. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response at pencil graphite electrode in acetate buffer, pH 4.8 at +1.13 V (vs. Ag/AgCl) (a preconcentration step being carried out at a fixed potential of +0.70 V for 180 s). The process could be used to determine BaP concentrations in the range 0.25-1.25 mu M, with a detection limit of 0.027 mu M (6.82 mu g L-1). The applicability to assay of spiked human urine samples was also illustrated.