Esin Canel

Hydrogen ion-selective poly(vinyl chloride) membrane electrode based on a p-tert-butylcalix[4]arene-oxacrown-4.

A hydrogen ion-selective poly(vinyl chloride) (PVC) membrane electrode was developed using p-tert-butylcalix[4]arene-oxacrown-4 as ionophore. Apart from the ionophore, plasticisers and lipophilic anions were blended, in various proportions, with PVC in tetrahydrofurane and mixtures so prepared were poured onto glass surfaces to form the membrane. 2-Nitrophenylpentylether has proved to be the best alternative as plasticiser and the lipophilic anions tried have turned out to have an adverse effect on the pH response. The electrode of the optimum characteristics had a composition of 2% p-tert-butylcalix[4]arene-oxacrown-4, 68.3% o-NPPE and 29.7% PVC. The electrode showed an apparent Nernstian response in the pH range 2-11 with a slope of 54.2+/-0.4mVpH(-1) at 20+/-1 degrees C. It has a rapid potential-response to changes of pH, high ion selectivity towards lithium, sodium and potassium, and other characteristics comparable to those reported for the conventional pH glass membrane electrode. It appears to be a suitable potentiometric indicator electrode specifically for hydrofluoric acid solutions.

Redox pathways of aliskiren based on experimental and computational approach and its voltammetric determination

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%.

Temperature Programmed Pyrolysis and Supercritical Extraction of Turkish Lignites

Abstract The aim of this study was to determine product evolution rate and volatile product distribution with the capillary gas chromatographic detection during temperature programmed pyrolysis of some Turkish lignites. The pyrolysis examinations conducted under non-isothermal conditions at a low heating rate of 2 K/min up to 550°C can show that the typical volatile product evolution begins at about 350°C and reaches its maximum value at approximately 440°C. n-Paraffins and 1-olefins in aliphatic fraction of pyrolysis products were classified as a carbon number. n-Paraffins up to about C30 were observed among the products and these were accompanied by smaller but significant amounts of 1-olefins. Supercritical toluene extraction was also performed on the lignite samples and the conversion degree and the extract yield results were compared with the results of pyrolysis.

Characterization of the Göynük oil shale-derived asphaltenes and pre-asphaltenes by 1H and 13C nuclear magnetic resonance and by gas chromatography

Abstract The oil shale-derived asphaltenes and pre-asphaltenes of the Goynuk oil shale have been studied by means of the nuclear magnetic resonance technique (NMR) and gas chromatography. 1 H and 13 C NMR spectra were obtained on the latter using the inverse gated heteronuclear decoupling pulse sequence. The study and quantitative determination of the different types of hydrogen and carbon atoms present in the samples have shown that the oil shale-derived asphaltenes and pre-asphaltenes are composed basically of aliphatic hydrocarbons, olefins and the contribution, though less important, of aromatic hydrocarbons. Taking into account both the NMR and chromatographic analysis, it can be said that asphaltenes and pre-asphaltenes are formed by similar compounds which mainly differ in the size of the components. These ones are larger in the pre-asphaltenes. It was also observed that with increasing pressure the size of extracted structures increases. The maximum in the recovered aromatic structures obtained under 250 bar and the decrease when the pressure is increased to 300 bar could be explained by rearrangement reactions.

PVC-membran elektrotların performansına plastikleştirici ve iletkenlik arttırıcıların etkisi

Analitik kimyada bir turun matriks ortaminda dogru ve kesin tayini cok onemlidir. Numunelerde mevcut eser turlerin tayini icin genellikle cok pahali ve karmasik cihazlar kullanilmaktadir. Halbuki elektrotlarla tayin, hem daha pratik hem de daha ucuz olmaktadir. Bu durumda cok sayida ture duyarli ve secici elektrotlarin hazirlanmasi ve cesitli matriks ortaminda turlerin tayininin yapilabilmesi icin yontem gelistirilmesi oldukca onemli hale gelmektedir. Bu projede notral tasiyici (iyonofor) olarak makrosiklik bilesikler kullanilarak cesitli iyonlara duyarli bir cesitli PVC-elektrotlar gelistirilmesi amaclanmistir. Bu elektrotlarin omru, cevap suresi, optimum calisma araligi ve diger bazi cevap karakteristikleri arastirilmistir. Hazirlanan bu tip elektrotlarin membrani, iyonofor yaninda polimerik madde, plasiklestirici ve iletkenlik arttirici gibi bir matriks icermektedir. Matriks icinde bulunan bu bilesenlerin, ozellikle de plasiklestirici ve iletkenlik arttirici cinsinin ve oranlarinin membranin performansina etkisi oldukca fazladir. Nernst cevabi elde edilen elektrot hazirlandiginda, bunun calisma araligi, cevap suresi, omru gibi cesitli parametreler belirlenmistir. Hazirlanan elektrodun tayin edilecek iyon disinda diger iyonlara duyarligi tespit edilerek cesitli yontemlerle bu katyonlar icin elektrodun secicilik katsayilari hesaplanmistir. Ayrica hazirlanan bu elektrodun cesitli analitik amaclar icin, kullanilip kullanilamayacagi da incelenmistir. AbstractThe determination of a species in a matrix media is very important in analytical chemistry. There are expensive and sophisticated equipment used in the detection of the trace species present in the samples. These type of determinations can be made both cheap and practical by the use of electrodes. Therefore development of techniques with the use of the electrodes sensitive to the certain species in different matrix is of great importance. The goal of this project is the construction of ion sensitive electrodes with the use of neutral carriers (ionopheres). The lifetime, response time, optimum working range and other response characteristics of these electrodes were also be investigated. The membrane of these electrodes contains a matrix made of a polymeric material, plasticiser and conductive material as well as an ionophere. The type and the ratio of the material present in the matrix have an important effect upon the performance of the electrode. In this study an electrode with Nerstian behaviour has been constructed and its working range, response time and other parameters were evaluated. The selectivity of the electrode towards the ion of the interest and towards other ions was deduced and the selectivity coefficients of the electrode towards various anions was computed. The suitability of the electrode prepared for various analytical purposes was also evaluated.

Piromellitik Asitle Lehimde Kurşun Tayini

This study is concerned with the use of new titrant in the determination of lead in solder . The titrant chosen was pyromellitic acid. The titrations were carried out at pH 3.5 at 250C constant temperature and the ionic strength of the medium was adjusted with sodium nitrate.The determinations carried out on three standard and one commercial solder samples, revealed that the determination of lead can be made with high accuracy by the use of this titrant . The data also show that pyromellitic acid is a much better titrant than sulfuric acid . The data obtained was found to be in good compliance with those obtained with atomic absorption spectrophotometry. This new titration method developed is highly rapid and the results were found accurate and repeatable.