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Öğe Application of pencil graphite electrode for voltammetric simultaneousdetermination of ascorbic acid, norepinephrine and uric acid in real samples(Batman Üniversitesi, 2018) Levent, Abdulkadir; Önal, GünayÖğe Electroanalytical investigation of antineoplastic drug vinorelbine at pencil graphite electrode in surfactant media(Turkish Chemical Society, 2019) Önal, Günay; Levent, Abdulkadir; Şentürk, ZühreVinorelbine (sold under the brand name Navelbine), one of the semisynthetic derivatives of Vinca alkaloids, has been widely used either alone or in combination with other drugs in the tre- atment of leukemia, lymphoma, advanced testicular cancer and Kaposi's sarcoma. From the electrochemical point of view, only one study that was quite old has been reported on its voltammetric characteris- tics so far (Brett et al.). Keeping the above knowledge in mind, in the present study, a novel application of single-use pencil graphite (PG) electrode is introduced for the determination of Vinorelbine. The electrochemical oxidation of this compound was first investigated by cyclic voltammetry in aqueous solutions. Special attention was given to the use of adsorptive stripping vol- tammetry at a surface of PG electrode and glassy carbon (GC) one (for comparison purpose) in aqueous solutions over the pH range of 2.0-12.0 both without and with the addition of different charged surfactants. The sensitivity of the stripping voltammet- ric measurements was significantly improved when the anionic (sodium dodecylsulfate, SDS) and cationic (tetra-n-butylammo- nium bromide, TBAB) surfactants were present in the Vinorelbi- ne-containing electrolyte solution at pH 2.0-4.0 and pH 9.0-10.0, respectively, by using PG electrode. Using square-wave stripping mode, Vinorelbine yielded a well-defined voltammetric response in Britton-Robinson buffer pH 10.0 containing 3×10−3 M TBAB at +0.75 V (vs. Ag/AgCl) (after 120 s accumulation at +0.0 V). The process could be used to determine this compound in the concentration range of 2.3×10−8 – 5.8×10−6 M, with a detection limit of 7.5×10−9 M (base-5.8 ng mL1−). The proposed method was successfully applied to pharmaceutical formulations and the spiked human urine samples.Öğe Simultaneous electrochemical evaluation of ascorbic acid, epinephrine and uric acid at disposable pencil graphite electrode: Highly sensitive determination in pharmaceuticals and biological liquids by differential pulse voltammetry(Elsevier, 2018) Levent, Abdulkadir; Önal, GünayAim and Objective: As is known, AA, EP and UA can also coexist in biological fluids. Therefore, the determination of the levels of these compounds in biological fluids is extremely important both for the diagnosis and treatment of the related diseases. In the presence of many interfering substances in biological fluids such as blood and urine samples, it is very important that these compounds can be selectively analyzed. Materials and Methods: All electrochemical experiments were performed using an Autolab PGSTAT 128N potentiostat. Before beginning the electrochemical measurements, the PGE was activated. The electrochemical pretreatment of PG was exercised by anodically +1.40 V for 60 s. Then, measurements were performed with CV (-0.4 V to 1.2 V) and DPV (-0.2 V to 0.7 V) for single and simultaneous voltammetric behaviour of AA, EP, and UA in the electrochemical method. Results: The anodic peak potentials of AA and UA were observed at about +0.32 V and +0.62 V, respectively. On the other hand, for EP, while anodic peak potential was observed at about +0.53 V, in the reverse scan, cathodic peak potentials were observed at about +0.41 V and +0.007 V. The39 reduction peak observed at +0.3 V with the oxidation peak observed at +0.53 V are the reversible peaks. In the method developed for the electrochemical simultaneous determination of AA, EP and UA using PGE with DPV technique in BR buffer solution (pH 4.0), the anodic peak potentials are sufficiently separated from each other. Conclusion: A voltammetric method was developed for the simultaneous determination of AA, EP and UA with PGE for the first time. Here, the most important thing is that the simultaneous determination of AA, EP and UA was successfully achieved with that targeted voltammetric method which was sensitive, low-cost, practical and well-repeated; and that these were proven to be selectively applicable in pharmaceutical products and biological liquids.Öğe Miyosmin’nin camsı karbon elektrot ile elektrokimyasal özelliklerinin incelenmesi ve miktar tayini(BioTechBioChem, 2020) Önal, Günay; Keskin, Ertuğrul; Levent, AbdulkadirTütün bitkisi olarak bilinen nikotin türleri (Solanaceae) dünyada en yaygın kullanılan farmasötik bitkilerdir[1]. Miyosmin, çeşitli doğal Nikotin ve ticari tütün çeşitlerinde (Nicotiana tabacum) bulunan yapısal olarak ilişkili küçük alkaloidler olan nornikotin, anabasin, anatabin grubundadır[2]. Nikotin cinsinin tüm üyeleri, tütün bitkileri ve ürünlerinin yaygın insan kullanımından sorumlu olan nikotin üretir[3]. Alkaloid miyosmin sadece tütün ürünlerinde değil aynı zamanda çeşitli yiyeceklerde de mevcuttur. Miyosmin, insan hücrelerinde genotoksiktir ve karsinojenik potansiyele sahip reaktif ara maddeler vermek üzere kolayca nitrozlanır ve peroksidasyona uğrar[4]. Miyosminin prevalansı nedeniyle, risk değerlendirmesi için metabolizması ve aktivasyonu üzerine araştırmalara ihtiyaç vardır[5]. Bu çalışmada, tütün alkaloidlerinden Miyosmin tayininde camsı karbon elektrot uygulaması sunulmuştur. Miyosmin´in elektrokimyasal indirgenmesi farklı destek ve geniş bir pH aralığında, CV (dönüşümlü voltametri) ve Diferansiyel Puls Voltametri (DPV) teknikleri ile araştırıldı.Öğe Application of bismuth film electrode in determination of Loratadine by cathodic stripping voltammetry in the presence of cationic surfactant(ICNTC, 2020) Önal, Günay; Altunkaynak, Yalçın; Levent, AbdulkadirLoratadine, histamine - H1 antihistamine receptors it is being used for many years in the treatment of an allergic condition illustrating the effects on[1]. When the literature is reviewed, there are limited number of studies on Loratadine based on electrochemistry [2-5]. Stripping voltammetry is a very sensitive and selective method for determining drugs and organic / inorganic substances in biological fluids. The electrochemical behavior of Loratadine with BiFE in different supporting electrolyte and pH values, and its performance characteristics in electroanalytical determinations were investigated by cyclic voltammetry and linear sweep cathodic stripping voltammetry (LS-CSV) methods. LS-CSV measurements on the BiFE surface of 6.5x10-4 M Loratadine in 0.04 M BR buffer (pH 7.0) and 4 mM cationic surfactant (CTAB) were taken between 0.0 V and -2.0 V. Loratadine gave a voltammetric response about at -1.486 V. The limit of detection was found LOD = 1.2x10-7 M* at the BIFE surface at liner concentration range [1.305x10-6 M – 14.3x10-6 M, r = 0,998* (n = 11)]. This voltammetric method, developed under optimum conditions, has been successfully applied to pharmaceutical formulations of Loratadin as fast, easy to apply, sensitive and environmentally friendly.Öğe Application of a pencil graphite electrode for voltammetric simultaneous determination of ascorbic acid, norepinephrine, and uric acid in real samples(TÜBİTAK, 2018-04-27) Levent, Abdulkadir; Önal, GünayA pencil graphite electrode (PGE) was used for the simultaneous detection of ascorbic acid (AA), norepinephrine (NE), and uric acid (UA) by differential pulse voltammetry and cyclic voltammetry. The anodic peaks of AA, NE, and UA in their mixture can be well separated in 0.1 M Britton–Robinson buffer solution at pH 4.0. The effects of various experimental parameters such as pH, scan rate, and voltammetric parameters on the voltammetric response of these compounds were investigated. Under optimum conditions, linear calibration graphs were obtained from the AA, NE, and UA concentration ranges, which were 100–800 nM, 20–170 nM, and 40–175 nM, respectively. The detection limits for AA, NE, and UA were 27 nM, 4 nM, and 10 nM in the form of a mixture at the PGE. This electrode shows great analytical performance characteristics, corresponding repeatability and recovery for the simultaneous determination of these compounds. PGE, which was used for the first time in this method, has been successfully applied for the assay of UA in human urine samples with the aim of determining AA and NE in pharmaceutical drugs.Öğe Simultaneous electrochemical evaluation of ascorbic acid, epinephrine and uric acid atdisposable pencil graphite electrode: Highly sensitive determination in pharmaceuticals and biolocigial liquids by differential pulse voltammetry(Batman Üniversitesi, 2018) Önal, Günay; Levent, AbdulkadirÖğe Katyonik sürfaktan madde varlığında bizmut film elektrot kullanarak desloratadinin elektrokimyasal olarak indirgenmesi: Lineer taramalı sıyırma voltametrisi ile ilaç ve idrar numunelerine uygulanması(BioTechBioChem, 2020) Altunkaynak, Yalçın; Önal, Günay; Levent, AbdulkadirHistamin, mide salgısının güçlü bir uyarıcısı olan biyolojik bir amin olup etkili bir nörotransmitterdir[1]. Literatürde biyolojik sıvı ve ilaç şekillerinde desloratadin (DESL) analizi için önerilen elektrokimyasal yöntemlerin temel alındığı teknikleri kullanıldığı birkaç çalışma vardır[2-6]. Bu çalışmada, ikinci nesil antihistaminikler grubundan olan DESL’nin elektrokimyasal özellikleri, Bizmut Film eleketrot (BİFE) kullanılarak sulu ve sulu/yüzey aktif madde çözeltilerinde gerçekleştirildi. Bu bileşik dönüşümlü voltametri ile yaklaşık -1.65 V da tersinmez ve adsorpsiyon kontrollü bir indirgenme piki göstermiştir. Katyonik yüzey aktif madde (setiltrimetilamonyum bromür, CTAB) ilavesinin desloratadinin indirgeme akım sinyalini arttırdığı, anyonik (sodyum dodesilsülfat, SDS) ve iyonik olmayan (Tween 80) yüzey aktif maddelerinin ise ters etki sergilediği bulundu. Linear taramalı adsorptif sıyırma voltametrisi kullanılarak akım, 5 mM CTAB içeren BrittonRobinson tamponunda, pH 8.0'de 0.1 ile 4 µM derişim aralığında doğrusal bir bağıntı göstermiştir(Şekil 1). Şekil 1. 0.1- 4 μM derişim aralığında BR tampon( pH 8.0 / 5 mM CTAB içeren) ortamında lineer taramalı sıyırma voltametri eğrileri Bu çalışmada geliştirilen yöntem, farmasötik preparatlarda ve idrar örneklerinde herhangi bir ayırma işlemi yapılmadan DESL analizi için başarılı bir şekilde uygulanmıştır.
