Levent Pelit

Biosorption of Cu(II) and Pb(II) ions from aqueous solution by natural spider silk

Aside from its excellent mechanical properties, spider silk (SS) would offer an active surface for heavy metal interaction due to its rich protein structure. The present study describes the potential use of natural (SS) as a sorbent of heavy metals from aqueous solutions. Single and multi-species biosorption experiments of heavy metals by natural SS were conducted using batch and column experiments. The biosorption kinetics, in general, was found to follow the second-order rate expression, and the experimental equilibrium biosorption data fitted reasonably well to Freundlich isotherm. From the Freundlich isotherm, the biosorption capacities of Cu(II) and Pb(II) ions onto SS were found as 0.20 and 0.007 mmol g⁻¹, respectively. The results showed a decrease in the extent of metal ion uptake with lowering the pH.

A novel polythiophene – ionic liquid modified clay composite solid phase microextraction fiber: Preparation, characterization and application to pesticide analysis

This report comprises the novel usage of polythiophene - ionic liquid modified clay surfaces for solid phase microextraction (SPME) fiber production to improve the analysis of pesticides in fruit juice samples. Montmorillonite (Mmt) clay intercalated with ionic liquids (IL) was co-deposited with polythiophene (PTh) polymer coated electrochemically on an SPME fiber. The surface of the fibers were characterized by using scanning electron microscopy (SEM). Operational parameters effecting the extraction efficiency namely; the sample volume and pH, adsorption temperature and time, desorption temperature and time, stirring rate and salt amount were optimized. In order to reveal the major effects, these eight factors were selected and Plackett-Burman Design was constructed. The significant parameters detected; adsorption and temperature along with the stirring rate, were further investigated by Box-Behnken design. Under optimized conditions, calibration graphs were plotted and detection limits were calculated in the range of 0.002-0.667ng mL(-1). Relative standard deviations were no higher than 18%. Overall results have indicated that this novel PTh-IL-Mmt SPME surface developed by the aid of electrochemical deposition could offer a selective and sensitive head space analysis for the selected pesticide residues.

Preparation and application of a polythiophene solid-phase microextraction fiber for the determination of endocrine-disruptor pesticides in well waters

A robust solid-phase microextraction fiber was fabricated by electropolymerization of thiophene on a stainless steel wire. This fiber was applied for the determination of endocrine-disruptor pesticides, namely, chlorpyrifos, penconazole, procymidone, bromopropylate, and λ-cyhalothrin in well waters by a headspace solid-phase microextraction procedure. Operational parameters, namely, pH, sample volume, adsorption temperature and time, desorption temperature, stirring rate, and salt amount were optimized as 7.0, 8 mL, 70°C and 20 min, 250°C, 600 rpm, and 0.3 g/mL, respectively. The separation power of GC was coupled with the excellent sensitivity of the developed fiber enabling us to determine pesticide mixtures simultaneously in a ng/mL range. The LOD was in the range of 0.02-0.64 ng/mL. The method was successfully applied for the selective and sensitive determination of target pesticides in well water samples with acceptable recovery values (92-110%). The polythiophene fiber gives satisfactory results compared with commercial fibers. Commonly used pesticides with different polarities were chosen as representative compounds to search the applicability of the fiber for well water analysis collected from vineyards.

Preparation and characterization of sodium dodecyl sulfate doped polypyrrole solid phase micro extraction fiber and its application to endocrine disruptor pesticide analysis.

A robust in house solid-phase micro extraction (SPME) surface has been developed for the headspace (HS)-SPME determination of endocrine disruptor pesticides, namely, Chlorpyrifos, Penconazole, Procymidone, Bromopropylate and Lambda-Cyhalothrin in wine sample by using sodium dodecylsulfate doped polypyrrole SPME fiber. Pyrrole monomer was electrochemically polymerized on a stainless steel wire in laboratory conditions in virtue of diminishing the cost and enhancing the analyte retention on its surface to exert better selectivity and hence the developed polymerized surface could offer to analyst to exploit it as a fiber in headspace SPME analysis. The parameters, mainly, adsorption temperature and time, desorption temperature, stirring rate and salt amount were optimized to be as 70°C and 45min, 200°C, 600rpm and 10gL(-1), respectively. Limit of detection was estimated in the range of 0.073-1.659ngmL(-1) for the pesticides studied. The developed method was applied in to red wine sample with acceptable recovery values (92-107%) which were obtained for these selected pesticides.

Development of a gas chromatographic method for the determination of Chlorpyrifos and its metabolite Chlorpyrifos-oxon in wine matrix

A reliable method has been developed for the determination of Chlorpyrifos (CP) and its metabolite Chlorpyrifos-oxon (CPO) in wine sample using pulsed splitless technique coupled with gas chromatography by using electron capture detector. In this study, a quick, easy and cheap sample preparation method (QuEChERS) based on liquid extraction with acetonitrile, followed by dispersive solid phase extraction using primary secondary amine was tested for the separation and quantification of CP and CPO in wine samples. The accuracy of the developed method was tested upon recovery studies and it was calculated as (92.3 ± 18.2)% for CP and (96.6 ± 16.1)% for CPO. LOD and LOQ values of CP were found as 0.04 and 0.15 ng/mL and 0.49 and 1.62 ng/mL for CPO respectively. By using the pulsed splitless injection mode, the sensitivity of the determination of CP and its metabolite CPO in wine samples was improved compared to splitless technique. CP content of analyzed wine sample was found as 2.05 ± 0.15 ng/mL with a RSD of 7.6% and CPO content was found as 4.99 ± 0.15 ng/mL with a RSD of 3.0% (n=3). The expanded measurement uncertainties were calculated as 17% and 6% for CP and CPO, respectively.

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.

Head space voltammetry: A novel voltammetric method for volatile organics and a case study for phenol

Present paper describes the results of a novel method which combines the Head space (HS) preconcentration of the analyte on the electrode prior to the voltammetric analysis. Thereafter, the method was called HS-Voltammetry. The performance of the method was tested upon using an electroactive and volatile molecule, phenol molecule, which gives an oxidation peak at conventional electrodes. In this study, a glassy carbon electrode was modified with polypyrrole by electropolymerization and then, the electrode was placed over the solution in a sealed vial heated gently on a hotplate with a stirrer for phenol determination. By controlling the thickness of the polymeric coating and optimizing preconcentration parameters such as vial pH and temperature, stirring rate and exposure time, a very consistent (5.2% at 5.0×10(-7) M) fraction of the analyte can be extracted during a predetermined time. The oxidation peak current at 0.8 V depended linearly on the phenol concentration over a wide range (3 orders of magnitude). The detection limit was estimated as 7.0×10(-8) M at 60 °C (S/N=3) which is well below the limit set by the European Community for phenols in wastewaters (ca. 5×10(-6) M). The effect of other phenolic compounds was also examined and it was shown that head space preconcentration eliminated the interference of non-volatile phenolic acids studied. For volatile phenolic compounds, the selectivity can be maintained in cases when isolated peaks are obtained for each component. The proposed method has been applied successfully for the determination of phenol in artificial wastewater and recovery percentage was calculated as 93%.

A green photometric method for determination of mercuric ions in saline samples by a single-drop microextraction technique

This study describes a rapid, simple and sensitive spectrophotometric method for determination of Hg(II) ions in saline samples by a single-drop microextraction (SDME) technique. The method is based on the extraction of dithizone (DTZ) complex of mercury(II) into an undecanol droplet which serves as the organic phase, and then the absorbance of the colored complex is measured at 490 nm by using a microvolume quartz cuvette. This procedure provides a simple, rapid, cost-efficient and, most of all, a green method for detecting mercuric ions by minimizing the organic solvent consumption. A variety of parameters affecting the signal, such as pH, DTZ concentration, sample and extraction solvent volume, extraction time and temperature and salt effects were optimized. Under optimized conditions the linear range was found between 3.2 × 10−8 and 5.0 × 10−7 mol L−1 (6.4–100.8 μg L−1) and the detection limit was calculated as 9.6 × 10−9 mol L−1 (1.9 μg mL−1) attained by a high enrichment factor of 203. The performance and accuracy of the method were compared with those of atomic fluorescence spectrometry. Validation of the proposed method was performed for determination of mercury in saline samples including sea water, mineral water, thermal spring water, and table and rock salt samples, which is difficult to analyze by conventional methods.

Polythiophene–Clay Composite Solid-Phase Microextraction Fiber: Preparation, Characterization, and Application to the Determination of Methanol in Biodiesel

ABSTRACT A novel polymer-clay composite solid phase microextraction fiber is reported for the adsorption of methanol in biodiesel with subsequent determination by gas chromatography coupled with a flame ionization detector. The fiber was fabricated using a stainless steel wire that was subjected to electropolymerization in 0.1 mol NaClO4 containing thiophene and montmorillonite clay dispersed in acetonitrile. Electrochemical deposition was maintained by cycling the potential from −0.2 to +2.2 V at a scan rate of 50 mV/sec. Examination of the surface by scanning electron microscopy revealed that the fiber had a porous surface suitable for the adsorption of volatile analytes. The properties of the fiber were investigated by thermogravimetric analysis and infrared spectroscopy that showed that the clay was inserted in the structure. The fiber was exposed to methanol in biodiesel. The adsorption time, adsorption temperature, and desorption temperature were optimized. Under the optimized conditions, the linear dynamic range for methanol extended from 0.029 to 0.24% (m/m) with a limit of detection of 0.009% (m/m). The method was employed for the analysis of biodiesel and the results were validated with a standard EN 14110 method.

Adsorptive Cathodic Stripping Voltammetric Determination of Boscalid in the Presence of Cobalt Ions at a Pencil Lead Electrode

ABSTRACT Here is described a novel voltammetric method for boscalid. Boscalid is a broad-spectrum fungicide known to be electrochemically inactive. However, it forms complexes with cobalt(II) through its pyridine carboxamide group that allows its indirect determination by adsorptive cathodic stripping voltammetry after deposition at positive potentials. The catalytic character of the reduction peak at −1.2 V was established by the mechanistic studies. After optimization of the parameters, calibration relationships were obtained at nanomolar concentrations and the method was used to analyze tomato juice and tomato paste with satisfactory recoveries.