Süleyman Koçak

Centri-voltammetric determination of molybdenum

Centri-voltammetry is a method developed in the last decade which combines the advantages of centrifugation and voltammetry and hence provides a practical way for application of co-precipitation in trace analysis allowing direct voltammetric scan. The present study describes another application of the centri-voltammetric method for the determination of biologically essential trace elements, in particular, molybdenum ion. For this purpose, a dual-functional voltammetric cell adjustable to the centrifuge was designed and utilized in the determination of molybdenum ions with various carrier reagents, i.e. oxine, pyrogallol red, and cupferron. Optimization studies include solution properties as well as voltammetric measurement and centrifugal parameters. Among the reagents studied, the best results were obtained with pyrogallol red and the reduction peak current of the complex was utilized for analytical purposes. The limit of detection from calibration curves was calculated to be 9.4 × 10−9 M and a better sensitivity was obtained in the presence of chlorate ions that are known to have a catalytic effect on the reaction. The method was employed in the determination of molybdenum in milk samples and the results were compared with those obtained by the ICP-MS method.

A spectrophotometric method for determination of molybdenum in water samples by using pyrogallol red and a water soluble ionic liquid

The present study describes a simple and sensitive spectrophotometric method for the determination of molybdenum in real water samples. The method is based on the hyperchromic and bathochromic effect of an ionic liquid namely, 1-methyl-3-octadecyl-imidazolium bromide (C18mimBr), on molybdenum ion (Mo(VI)) and pyrogallol red (PGR) complex. The ternary complex of Mo–PGR–C18mimBr displays a distinct absorption peak with excellent analytical characteristics and offers the advantages of simplicity for the determination of Mo(VI) ions, without any need for a solvent extraction step. The limit of detection (LOD) and limit of quantification (LOQ) of the method were calculated as 0.74 ng mL−1 and 2.47 ng mL−1 respectively. The method was validated and applied successfully to the determination of Mo(VI) ions in real water samples. The interference of ferric ions was shown to be removed from samples with less ionic content by using an ion exchange resin prior to the analysis, and the performance of the method was compared with that of ICP-MS.

Determination of oleuropein using multiwalled carbon nanotube modified glassy carbon electrode by adsorptive stripping square wave voltammetry.

A multi-walled carbon nanotube modified glassy carbon electrode was used to prepare an electrochemical sensing platform for the determination of oleuropein. Results showed that, the accumulation of oleuropein on the prepared electrode takes place with the adsorption process. Electrochemical behavior of oleuropein was studied by using cyclic voltammetry. Compared to the bare GCE, the oxidation peak current of oleuropein increased about 340 times at MWCNT/GCE. Voltammetric determination of oleuropein on the surface of prepared electrode was studied using square wave voltammetry where the oxidation peak current of oleuropein was measured as an analytical signal. A calibration curve of oleuropein was performed between 0.01 and 0.70µM and a good linearity was obtained with a correlation coefficient of 0.9984. Detection and quantification limits of the method were obtained as 2.73 and 9.09nM, respectively. In addition, intra-day and inter-day precision studies indicated that the voltammetric method was sufficiently repeatable. Finally, the proposed electrochemical sensor was successfully applied to the determination of oleuropein in an olive leaf extract. Microwave-assisted extraction of oleuropein had good recovery values between 92% and 98%. The results obtained with the proposed electrochemical sensor were compared with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis.

Enhanced optical oxygen sensing using a newly synthesized ruthenium complex together with oxygen carriers

In this article, an emission based, simple and fast method is proposed for the determination of gaseous oxygen. A newly synthesized fluorophore, dichloro-{2,6-bis[1-(4-dimethylamino-phenylimino) ethyl]pyridine}ruthenium(II) has been used for oxygen sensing together with oxygen carrier perfluorochemicals (PFCs) in silicon matrix. It should be noted that the solubility of oxygen in fluorocarbons is about three to ten times large as that observed in the parent hydrocarbons or in water, respectively. Employed PFCs are chemically and biochemically inert, have high dissolution capacities for oxygen, and, once doped into sensing film, considerably enhance the response of sensing agent.

Electrochemical Determination of Hydrazine at Gold and Platinum Nanoparticles Modified Poly(L-Serine) Glassy Carbon Electrodes

ABSTRACT L-serine monomer was polymerized electrochemically on a glassy carbon electrode by cyclic voltammetry. After L-serine polymerization, gold and platinum metal nanoparticles were doped by electrochemical reduction on the surface. The modified electrodes were characterized by using scanning electron microscopy and electrochemical impedance spectroscopy. The electrochemical behavior of hydrazine oxidation at the electrodes was investigated in 0.1 M pH 7.0 phosphate buffer. Hydrazine oxidation peaks were observed at 650, 399, 280, and −395 mV at the bare glassy carbon, poly(L-serine) modified glassy carbon, gold nanoparticle modified poly(L-serine) film glassy carbon electrode, and platinum nanoparticles modified poly(L-serine) film glassy carbon electrode, respectively. The most active surface towards hydrazine oxidation was the platinum nanoparticle modified poly(L-serine) film glassy carbon electrode with a 1045 mV negative potential shift and approximately three-fold higher peak current. The hydrazine oxidation peak was shifted to a 370 mV negative potential with a 2.5 times higher current at the gold nanoparticle modified poly(L-serine) film glassy carbon electrode compared to the bare electrode. The linear concentration ranges were from 1.0 to 1000 µM and 0.5 to 1000 µM for the gold nanoparticle modified poly(L-serine) film glassy carbon and the platinum nanoparticles modified poly(L-serine) film glassy carbon electrodes with limits of detections of 0.5 and 0.2 µM, respectively.

Determination of Hydrazine at a Platinum Nanoparticle and Poly(Bromocresol Purple) Modified Carbon Nanotube Electrode

ABSTRACT Bromocresol purple was polymerized electrochemically at a carbon nanotube modified glassy carbon electrode and platinum nanoparticles were doped on the polymer film by electrochemical reduction. The modified electrodes were characterized by electrochemical impedance spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The oxidation of hydrazine was investigated at the platinum nanoparticle modified electrode in phosphate buffer. The results were compared with those obtained using other modified and bare electrodes. The best catalytic activity was obtained at the platinum nanoparticle modified electrode due to shift of the oxidation peak to more negative values and highest current. The peak potential and current for hydrazine were −445 mV and 175.5 µA, respectively. Linear calibration curves for hydrazine were obtained from 10 to 1000 mM. The limits of detection and quantitation for hydrazine were 1.0 and 3.0 mM, respectively.

Polymer Film Supported Bimetallic Au–Ag Catalysts for Electrocatalytic Oxidation of Ammonia Borane in Alkaline Media

Ammonia borane is widely used in most areas including fuel cell applications. The present paper describes electrochemical behavior of ammonia borane in alkaline media on the poly(p-aminophenol) film modified with Au and Ag bimetallic nanoparticles. The glassy carbon electrode was firstly covered with polymeric film electrochemically and then, Au, Ag, and Au–Ag nanoparticles were deposited on the polymeric film, respectively. The surface morphology and chemical composition of these electrodes were examined by scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that alloyed Au–Ag bimetallic nanoparticles are formed. Electrochemical measurements indicate that the developed electrode modified by Au–Ag bimetallic nanoparticles exhibit the highest electrocatalytic activity for ammonia borane oxidation in alkaline media. The rotating disk electrode voltammetry demonstrates that the developed electrode can catalyze almost six-electron oxidation pathway of ammonia borane. Our results may be attractive for anode materials of ammonia borane fuel cells under alkaline conditions.Graphical Abstract

Lead and copper removal using Kula volcanics from environmental waters

ABSTRACT The ability of Kula volcanics (the youngest volcanic rocks of western Anatolia) to remove Pb(II) and Cu(II) from aqueous solutions has been demonstrated, for the first time, in this study. The optimum parameters viz., pH, contact time and sorbent amount/solution volume ratio were evaluated using batch experiments. Langmuir isotherm model excellently described the sorption process and both of the ions followed pseudo-second-order kinetics. The method was applied to the natural river water samples and it was observed that the sorbent can successfully be used for the removal Pb(II) and Cu(II) ions with acceptable accuracy and precision.