Papers by ibrahim Hüdai Taşdemir
Journal of Pharmaceutical Analysis, Jun 1, 2012
In this study, square-wave adsorptive stripping voltammetry (SWAdSV) and differential pulse adsor... more In this study, square-wave adsorptive stripping voltammetry (SWAdSV) and differential pulse adsorptive stripping voltammetry (DPAdSV) were used for determination of ezetimibe (EZE) in the presence of 0.1 m K 2 HPO 4-Na 2 B 4 O 7 (1:1) supporting electrolyte. The well-defi ned peaks for SWAdSV were observed at accumulation time of 15 s, accumulation potential of-0.80 V, frequency of 15 Hz, pulse amplitude of 25 mV, potential increment of 4 mV. For DPAdSV, accumulation time of 15 s, accumulation potential of-0.85 mV, scan rate of 20 mV/s and pulse amplitude of 50 mV were found as the best apparatus parameters. EZE gave rise to a single voltammetric peak in the potential interval from-1236 to-1252 mV for SWAdSV and interval from-1190 to-1210 mV for DPAdSV. The developed methods were validated according to the ICH guideline and were found to be linear, sensitive, specifi c, precise and accurate. The linearity ranges of EZE for SWAdSV and DPAdSV are 33-596 ng/ml and 66-400 ng/ml, respectively. The developed method was applied successfully for the determination of EZE in tablet dosage form.
Philosophical Magazine, 2016
Electrical devices involve different types of diode in prospective electronics is of great import... more Electrical devices involve different types of diode in prospective electronics is of great importance. In this study, p-type Si surface was covered with thin film of TiO 2 dispersion in H 2 O to construct p-Si/TiO 2 /Al Schottky barrier diode (D1) and the other one with TiO 2 dispersion doped with zirconium to construct p-Si/TiO 2-Zr/ Al diode (D2) by drop-casting method in the same conditions. Electrical properties of as-prepared diodes and effect of zirconium as a dopant were investigated. Current-voltage (I-V) characteristics of these devices were measured at ambient conditions. Some parameters including ideality factor (n), barrier height (Φ B0), series resistance (Rs) and interface state density (Nss) were calculated from I-V behaviours of diodes. Structural comparisons were based on SEM and EDX measurements. Experimental results indicated that electrical parameters of p-Si/TiO 2 /Al Schottky device were influenced by the zirconium dopant in TiO 2. KEYWORDS p-si/Tio 2-zr/al structure; I-V characteristic; interface states; series resistance ARTICLE HISTORY
Journal of Food and Drug Analysis, 2014
The oxidation and reduction behavior of cefdinir (CEF) was studied by experimental methods and co... more The oxidation and reduction behavior of cefdinir (CEF) was studied by experimental methods and computational calculations at B3LYP/6-31þG (d)//AM1. Voltammetric studies were carried out based on two irreversible reduction peaks at approximately À0.5 and À1.2 V on a hanging mercury drop electrode (HMDE) and on one irreversible oxidation peak at approximately 1.0 V on a glassy carbon electrode (GCE) versus Ag/AgCl, KCl (3.0M) in BrittoneRobinson (BR) buffer at pH 4.2 and 5.0, respectively. Differential pulse adsorptive stripping voltammetric methods have been developed and validated for determination of CEF in different samples. The linear range was established as 0.25e40.0 mM for HMDE and 0.40e10.0 mM for GCE. Limit of quantification was calculated to be 0.20 and 0.26 mM for HMDE and GCE, respectively. These methods were successfully applied to assay the drug in tablets and human serum with good recoveries between 92.7% and 107.3% having relative standard deviation less than 10%.
IEEE Transactions on Electron Devices, 2014
The energy dependence of the interface states (N<sub>ss</sub>) and relaxation time (τ... more The energy dependence of the interface states (N<sub>ss</sub>) and relaxation time (τ) and capture cross section (σp) of N<sub>ss</sub> in (Au/PVC+TCNQ/p-Si) heterojunction were investigated using high-low frequency capacitance (C<sub>HF</sub>-C<sub>LF</sub>) and conductance method, which contains many capacitance/conductance [C/(G/ω)-V] plots. The C value of the heterojunction increases with decreasing frequency as almost exponentially due to the existence of N<sub>ss</sub> between metal and semiconductor. The N<sub>ss</sub> and τ values have been obtained in the (0.053- E<sub>v</sub>)-(0.785- E<sub>v</sub>)-eV energy range by considering the voltage-dependent surface potential obtained from the lowest measurable frequency C-V curve at 1 kHz. The magnitude of N<sub>ss</sub> ranges from 3.88×10<sup>12</sup> eV<sup>-1</sup>cm<sup>-2</sup> to 3.24×10<sup>12</sup> eV<sup>-1</sup>cm<sup>-2</sup>. In the same energy range, the value of τ ranges from 5.73×10<sup>-5</sup> to 1.58×10<sup>-4</sup> s and shows almost an exponential increase with increasing bias from the top of the valence band edge toward the midgap of semiconductor. The obtained N<sub>ss</sub> values from C<sub>HF</sub>-C<sub>LF</sub> and conductance methods are in good agreement with each other for the heterojunction. As a result, the mean value of N<sub>ss</sub> was found on the order of 10<sup>12</sup> eV<sup>-1</sup>cm<sup>-2</sup> and this value is very suitable for an electronic device.
Arabian Journal of Chemistry, 2016
Electrochemical behavior of cefditoren pivoxil (CTP) was studied via experimental electrochemical... more Electrochemical behavior of cefditoren pivoxil (CTP) was studied via experimental electrochemical methods and theoretical calculations performed at B3LYP/6-31+G(d)//AM1 level. Experimental studies were carried out based on an irreversible 4eÀ/4H+ reduction peak at ca. À0.8 V on hanging mercury drop electrode (HMDE) and irreversible 1eÀ/1H+ oxidation of CTP at ca. 0.8 V on glassy carbon electrode (GCE) versus Ag/AgCl, KCl (3.0 M) in Britton-Robinson buffer at pH 6.0 and 4.0, respectively. Tentative reduction and oxidation mechanisms were proposed based on computational and experimental results. Square-wave adsorptive stripping voltammetric methods have been developed and validated for quantification of CTP in different samples. Linear working range was established as 0.15-15.0 lM for HMDE and 1.0-50.0 lM for GCE. Limit of quantification (S/N = 10) was calculated to be (0.10 ± 0.02) lM and (0.80 ± 0.03) lM for HMDE and GCE, respectively. Methods were successfully applied to assay the drug in tablets and human serum with good recoveries between (99.2 ± 11.6) % and (102.5 ± 9.5) % having relative standard deviation less than 10%.
TURKISH JOURNAL OF CHEMISTRY, 2015
The reduction behavior of fenoxaprop-p-ethyl (FNX) was studied on a hanging mercury drop electrod... more The reduction behavior of fenoxaprop-p-ethyl (FNX) was studied on a hanging mercury drop electrode. FNX showed 2 reduction peaks at about-0.7 V and at about-0.9 V versus Ag/AgCl/3.0 M KCl in Britton-Robinson buffer at pH 4.8. Both reductions were irreversible and adsorption was effective. The reduction peaks were assigned to the reduction of C=N to CH-NH and the reduction of C=O to CH-OH. Square-wave voltammetry has been proposed and validated for quantification of FNX in different samples. The linear working range was established as 0.30-15.0 µ M. Limit of detection and limit of quantification were calculated as 0.07 µ M and 0.24 µ M, respectively. The proposed method was successfully applied for the determination of FNX in tap water, river water, and plant samples with recoveries between 95.7% and 99.6% showing a relative standard deviation of less than 15%.
Current Pharmaceutical Analysis, 2012
Bu tez calismasinda hipertansiyon tedavisinde kullanilan hidrokloratiyazit (HKA), indapamit (INDA... more Bu tez calismasinda hipertansiyon tedavisinde kullanilan hidrokloratiyazit (HKA), indapamit (INDA), peridopril (PER), moeksipril (MOE) ve zofenopril (ZOF) molekullerinin asili damla civa elektrot (ADCE) ve camsi karbon elektrot (CKE) yuzeylerindeki elektrokimyasal davranislari incelenmis, elektrot tepkimesine katilan elektron ve proton sayilari ile difuzyon katsayisi ve yuzey kaplama katsayisi hesaplanmistir. Deneysel calismalarda elde edilen veriler teorik hesaplama sonuclari ile birlikte degerlendirilerek indirgenme-yukseltgenme tepkimeleri icin olasi elektrot tepkime mekanizmalari onerilmistir. Elektrokimsal davranislari belirlenen ilac etken maddelerinin; tablet ve kapsul gibi farmasotik orneklerden ve kan, idrar ve serum gibi biyolojik numunelerden tek halde ve birlikte es zamanli nicel tayini icin voltametrik yontem gelistirme calismalari yapilmistir. Bu calismalardaher bir ilac etken maddesi icin diferansiyel puls voltametri (DPV), kare dalga voltametri (KDV), diferansiyel puls adsorptif siyirma voltametri (DPAdSV) ve kare dalga adsorptif siyirma voltametri (KDAdSV) yontemlerinin gelistirilmesine yonelik yontem ve cihaz parametrelerinin optimizasyonu yapilmistir. Optimum kosullarda yapilan kalibrasyon calismalarinda her bir madde icin dogrusal calisma araligi belirlenmistir. Kalibrasyon verilerinin en kucuk kareler yontemi kullanilarak degerlendirilmesi ilegelistirilen yontemlerin bazi validasyon parametreleri belirlenerek yontemler valide edilmistir. Gelistirilen yontemlerin tablet, serum ve idrar numunelerine uygulanmasi ile her bir yontemin performans parametreleri belirlenmistir. Yapilan uygulama calismalarinda yontemlerin geri kazanim degerlerinin % 100’e oldukca yakin oldugu, bununla birlikte gun ici ve gunler arasi akim ve potansiyel olcumlerinde bagil standart sapma degerlerinin % 10’dan kucuk oldugu belirlenmistir.Abstract In this study, electrochemical behavior of drug active materials found in some anti-hypertensive drugs namely as hydrochlorothiazide, indapamide, perindopril, moexiprile, and zofenopril used in treatment of hypertensive were investigated on hanging mercury drop electrode (HMDE) and glassy carbon electrode (GCE), number of electrons and protons participated to electrode reaction mechanism were calculated. Diffusion coefficient and surface coverage coefficient were also calculated. Experimental and theoretical results were coevaluated to propose the tentative electrode reaction mechanism to electrooxidation and electroreduction. Studies to develop voltammetric determination methods to be used to determine these drug-active materials from pharmaceuticals such as tablet and capsule form and biological samples such as blood, urine and serum samples were carried out. In such studies voltammetric methods such as; differential pulse voltammetry (DPV), square wave voltammetry (SWV), differential pulse adsorptive stripping voltammetry (DPAdSV) and square wave adsorptive stripping voltammetry (SWAdSV) were developed to determine each of these drug-active materials in both usage alone and combined with one another. In method development stage firstly optimization for experimental and equipmental variables were carried out. Calibration studies were done by using optimum variables after optimization studies. Calibration data were subjected to calculations in least square methods to evaluate some validation parameters and all methodswere validated. Developed methods were applied to tablet, serum and urine samples to find out the performance of proposed methods. In such applications, recovery values around 100 % were reconised and with-in-day (intra-day) and between-day (inter-day) test for current and potential reproducibility resulted with relative standart deviation of 10.0 %.
Biocontrol Science and Technology
The electrochemistry of moexipril (MOE) was studied by electrochemical methods with theoretical c... more The electrochemistry of moexipril (MOE) was studied by electrochemical methods with theoretical calculations performed at B3LYP/6-31 + G (d)//AM1. Cyclic voltammetric studies were carried out based on a reversible and adsorption-controlled reduction peak at -1.35 V on a hanging mercury drop electrode (HMDE). Concurrently irreversible diffusion-controlled oxidation peak at 1.15 V on glassy carbon electrode (GCE) was also employed. Potential values are according to Ag/AgCI, (3.0 M KCI) and measurements were performed in Britton-Robinson buffer of pH 5.5. Tentative electrode mechanisms were proposed according to experimental results and ab-initio calculations. Square-wave adsorptive stripping voltammetric methods have been developed and validated for quantification of MOE in pharmaceutical preparations. Linear working range was established as 0.03-1.35 microM for HMDE and 0.2-20.0 microM for GCE. Limit of quantification (LOQ) was calculated to be 0.032 and 0.47 microM for HMDE and GCE,...
International journal of electrochemical science
Anodic behavior of binary mixture of amlodipine besylate (AMD) and valsartan (VAL) was studied on... more Anodic behavior of binary mixture of amlodipine besylate (AMD) and valsartan (VAL) was studied on glassy carbon electrode based on the irreversible oxidation signal of AMD at 0.95 V and that of VAL at 1.15 V versus Ag/AgCl at pH 5.0 in Britton-Robinson buffer. Differential pulse voltammetric method was proposed to direct determination of AMD and VAL in pharmaceuticals and spiked human serum. Linearity for AMD was in the range from 1.0 μM to 35.0 μM and that for VAL was in the range from 1.5 μM to 32.0 μM when concentrations of AMD and VAL are increased simultaneously. Limit of detection and limit of quantification were found to be 0.31 μM and 1.03 μM, for AMD and 0.36 μM and 1.21 μM for VAL, respectively. The method was successfully applied with good recoveries between 90.8 % and 100.4 % with relative standard deviation less than 10 % for tablet samples and around 15 % for serum samples.
International journal of electrochemical science
Electrochemical reduction behavior of Zofenopril (ZFN) was studied via experimental electrochemic... more Electrochemical reduction behavior of Zofenopril (ZFN) was studied via experimental electrochemical methods and theoretical calculations performed at B3LYP/6-31+G (d)//AM1. Electrochemical studies based on one reversible and adsorption-controlled and two irreversible diffusion-controlled reduction peaks at-0.75 V,-1.3 V and-1.65 V, respectively on hanging mercury drop electrode (HMDE) versus Ag/AgCl, KCl (3.0 M) in Britton-Robinson buffer (BR) of pH 5.5. First peak (reversible one) was thought to be the reduction of carbonyl group activated by vicinal nitrogen and reoxidation to its original form, second reduction was supposed to be the reduction of other carbonyl and reduction of proton to hydrogen gas catalyzed by lone-pair electrons was proposed as third. Square-wave cathodic adsorptive stripping voltammetry has been developed and validated for quantification of ZFN in different samples. Linear working range was established as 0.03-1.05 µM. Limit of determination (LOD) was calculated to be 0.01 µM. Proposed method was successfully applied to assay the drug in tablets and human serum with good recoveries between 96.9 % and 101.4 % having relative standard deviation less than 10 %.
Collection of Czechoslovak Chemical Communications, 2011
Electrochemical oxidation and reduction properties of Moclobemide (MCB) were investigated at glas... more Electrochemical oxidation and reduction properties of Moclobemide (MCB) were investigated at glassy carbon electrode (GCE) and hanging mercury drop electrode (HMDE). Diffusion-adsorption behavior and some extra electrochemical parameters such as diffusion coefficient, number of transferred electrons and proton participated to its electrode mechanisms on both electrode and surface coverage coefficient were calculated from the results of cyclic voltammetry and square-wave voltammetry. Reversible catalytic hydrogen wave mechanism was proposed at HMDE and single two-electron/two-proton irreversible oxidation mechanism controlled by adsorption with some diffusion contribution at GCE was proposed. Experimental parameters were optimized to develop new, accurate, rapid, selective and simple voltammetric methods for direct determination of MCB in pharmaceutical dosage forms and spiked human serum samples without time-consuming steps prior to drug assay. In these methods, the lowest limit of ...
Environmental Toxicology and Chemistry, 2010
In the present study, an enrichment and separation method for the simultaneous determination of t... more In the present study, an enrichment and separation method for the simultaneous determination of trace amounts of Cu and Zn in water samples was developed. Copper and Zn ions found in water matrix in trace amounts were preconcentrated on Duolite XAD 761 resin without using any chelating agent and determined by flame atomic absorption spectrometer (FAAS). Experimental parameters such as pH, concentration of metal ions, amount of resin, and sample volume for quantitative determination of Cu and Zn ions were optimized. The elution process was performed by using 5 ml of 2 mol/L HCl solution. The preconcentration factors for Cu and Zn were found to be 160 and 200, respectively. Under optimized conditions, limit of detection for Cu and Zn were 2.46 and 3.54 µg/L, respectively. The Langmuir adsorption model was applied to describe the equilibrium isotherm. The Langmuir monolayer adsorption capacity of resin was estimated as 31.2 and 17.7 mg/g for Cu and Zn, respectively. The proposed method was successfully applied to determine the Cu and Zn content of various water samples.
Canadian Journal of Chemistry, 2013
The electrochemical behavior of metoprolol (MTP) was studied via experimental and computational a... more The electrochemical behavior of metoprolol (MTP) was studied via experimental and computational approaches. Theoretical calculations were performed at the B3LYP/6-31+G(d)//AM1 level whereas experimental studies were carried out on a hanging mercury drop electrode (HMDE) and glassy carbon electrode (GCE). According to the computational results, both HOMO and LUMO of MTP were located at the phenyl ring. Hence, oxidation and reduction are expected to take place at the phenyl ring. Experimental studies on HMDE were based on reversible reduction at approximately –1.4 V and studies on GCE were based on irreversible oxidation at approximately 0.9 V versus Ag/AgCl (3 mol L−1 KCl) in Britton−Robinson buffer. Voltammetric methods with and without adsorptive stripping modes were developed. Proposed methods were successfully applied to tablet solutions and spiked human serum samples. Results are satisfactory with recovery values between 94.5% and 102.5% and a relative standard deviation lower t...
Journal of the Brazilian Chemical Society, 2013
O comportamento eletroquímico do aliscireno (ALS) foi estudado por meio de métodos experimentais ... more O comportamento eletroquímico do aliscireno (ALS) foi estudado por meio de métodos experimentais eletroquímicos e cálculos teóricos realizados em nível B3LYP/6-31+G (d)//AM1. Estudos eletroquímicos foram baseados nos processos de redução reversível controlada por adsorção a ca. −1,5 V em eletrodo gotejante de mercúrio (HMDE) e de oxidação eletroquímica irreversível a ca. 1,0 V em eletrodo de carbono vítreo (GCE) do ALS vs. Ag/AgCl, KCl (3,0 mol L −1) em solução tampão Britton-Robinson pH 10 e 8, respectivamente. De acordo com os achados computacionais e experimentais, o ALS é esperado ser irreversivelmente oxidado na posição benzílica e reversivelmente reduzido nos grupos carbonila da amida. Métodos voltamétricos com e sem modo de redissolução adsortiva foram desenvolvidos e validados para quantificação do ALS em diferentes amostras. Limites de detecção e de quantificação para o ALS foram 6,3 × 10 −8 e 2,1 × 10 −7 mol L −1 por voltametria de pulso diferencial em HMDE e 1,2 × 10 −8 e 3,9 × 10 −8 mol L −1 por voltametria de onda quadrada com redissolução catódica adsortiva. Os métodos foram aplicados com sucesso em ensaios de fármacos em comprimidos e em sangue humano com boas recuperações, entre 91,7 e 102,3%, e desvio padrão relativo menor que 10%. Electrochemical behavior of aliskiren (ALS) was studied via experimental electrochemical methods and theoretical calculations performed at B3LYP/6-31+G (d)//AM1. Cyclic voltammetry studies were carried out based on the adsorption-controlled reversible reduction at ca. −1.5 V on hanging mercury drop electrode (HMDE) and irreversible electrochemical oxidation of ALS at ca. 1.0 V on glassy carbon electrode (GCE), vs. Ag/AgCl, KCl (3.0 mol L −1), in Britton-Robinson buffer at pH 10 and 8, respectively. According to computational and experimental findings, ALS is expected to be oxidized irreversibly at benzylic position and reduced reversibly at amide carbonyl groups. Voltammetric methods with and without adsorptive stripping mode were developed and validated for quantification of ALS in different samples. Limits of detection and of quantification for ALS were 6.3 × 10 −8 and 2.1 × 10 −7 mol L −1 for differential pulse voltammetry on HMDE and 1.2 × 10 −8 and 3.9 × 10 −8 mol L −1 for square-wave cathodic adsorptive stripping voltammetry. The methods were successfully applied to assay the drug in tablets and human serum with good recoveries, between 91.7 and 102.3%, having relative standard deviation less than 10%.
Asian Journal of Chemistry
Acta Chimica Slovenica
Electrochemical behavior and adsorption-diffusion properties of lercanidipine (LCN) on a glassy c... more Electrochemical behavior and adsorption-diffusion properties of lercanidipine (LCN) on a glassy carbon electrode (GCE) were investigated in a mixture of ethanol-Britton Robinson buffer (BR) using voltammetric methods. From experimental results LCN was found to be reduced irreversibly via a single four-electron process controlled mainly by diffusion with some adsorption contribution at about -0.65 V (vs. Ag/AgCl reference electrode). Therefore, a new, accurate, rapid, selective and simple square-wave cathodic adsorptive stripping voltammetric (SWCAdSV) method could be developed for direct determination of LCN in pharmaceutical preparations, spiked human urine and spiked human serum samples without time-consuming steps prior to drug assay. The peak current of the reduction wave linearly changed with the concentration of LCN in the concentration range between 4.0 × 10-8 molL-1 and 7.6 × 10-6 molL-1 in two different regions where optimum preconcentration potential and optimum preconcentration time were applied as -0.20 V and 90 s, respectively. The limit of detection (LOD) and the limit of quantitation (LOQ) values were found to be 2 × 10-8 molL-1 (0.01 mgL-1) and 6 × 10-8 molL-1 (0.04 mgL-1), respectively. The method was applied to determine the content of LCN in commercial pharmaceutical preparation, spiked human serum and spiked human urine. The method was found to be highly accurate and precise, having a relative standard deviation of less than 10% in all applications.
Acta chimica Slovenica, 2011
Electrochemical behavior and adsorption-diffusion properties of lercanidipine (LCN) on a glassy c... more Electrochemical behavior and adsorption-diffusion properties of lercanidipine (LCN) on a glassy carbon electrode (GCE) were investigated in a mixture of ethanol-Britton Robinson buffer (BR) using voltammetric methods. From experimental results LCN was found to be reduced irreversibly via a single four-electron process controlled mainly by diffusion with some adsorption contribution at about -0.65 V (vs. Ag/AgCl reference electrode). Therefore, a new, accurate, rapid, selective and simple square-wave cathodic adsorptive stripping voltammetric (SWCAdSV) method could be developed for direct determination of LCN in pharmaceutical preparations, spiked human urine and spiked human serum samples without time-consuming steps prior to drug assay. The peak current of the reduction wave linearly changed with the concentration of LCN in the concentration range between 4.0 × 10-8 molL-1 and 7.6 × 10-6 molL-1 in two different regions where optimum preconcentration potential and optimum preconcent...
Collection of Czechoslovak Chemical Communications, 2011
Risperidone (RPN) belongs to a class of antipsychotic drugs known as atypi-cal neuroleptics. It w... more Risperidone (RPN) belongs to a class of antipsychotic drugs known as atypi-cal neuroleptics. It was approved in 1993 for the treatment of schizophre-nia. In 2007, risperdal (RPL) was approved as the only drug agent available ... Collect. Czech. Chem. Commun. ...
Journal of Electroanalytical Chemistry, 2012
ABSTRACT In this article, for the first time the possibility of the application of an in situ pla... more ABSTRACT In this article, for the first time the possibility of the application of an in situ plated lead film electrode to adsorptive stripping voltammetric determinations of organic compounds at alkaline conditions, to pH of 13.3 was showed. As an example of the application of such electrode a procedure for disopyramide determination by adsorptive stripping voltammetry was elaborated. In non-deaerated solutions of ammonium buffer and sodium hydroxide, an in situ plated lead film electrode exhibited well-developed stripping voltammetric signals for disopyramide. For stabilization of Pb(II) at mild alkaline conditions, potassium sodium tartrate was added to an ammonium buffer used as a supporting electrolyte. The proposed voltammetric procedure was applied to disopyramide determination in pharmaceutical formulation.
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Papers by ibrahim Hüdai Taşdemir