Sevda Ayata

Separation and preconcentration of Pb(II) using ionic liquid-modified silica and its determination by flame atomic absorption spectrometry

A new method based on microcolumn packed with ionic liquid-modified silica combined with flame atomic absorption spectrometry has been developed for the determination of lead in environmental samples. Several factors influencing the preconcentration efficiency of lead and its subsequent determination, such as pH of the sample, flow rate, mass of ionic liquid, and interfering effect, have been investigated. Lead could be quantitatively retained by ionic liquid-modified silica in the pH range of 5-7, and then eluted completely with 3.0 mL 1.0 mol L(-1) HCl. The detection limit of this method for lead was 0.7 μg L(-1) with preconcentration factor of 185, and the relative standard deviation (RSD) was 4.2% at 0.1 μg mL(-1) Pb(II). This method has been applied for the determination of trace amount of lead in NIST standard reference material 2709 (San Joaquin Soil) and river water samples with satisfactory results.

Fluorescence-based sensor for Pb(II) using tetra-(3-bromo-4-hydroxyphenyl)porphyrin in liquid and immobilized medium

A new optical sensor for sensing of Pb(2+) in immobilized medium (PVC film) and ethanol medium was developed by using 5,10,15,20-tetra-(3-bromo-4-hydroxyphenyl)porphyrin (TBHPP) synthesized. The sensor-based TBHPP showed a linear response towards Pb(2+) in concentration range from 5x10(-6) to 4x10(-4)molL(-1) in PVC film and 5x10(-6) to 3x10(-4)molL(-1) in ethanol medium, with a working pH 7. The detection limit was 2x10(-8) and 4x10(-8)molL(-1) for Pb(2+) in PVC film and ethanol medium respectively. The response time of Pb(2+) was found as 4min for PVC film and 2min for ethanol medium. The sensor developed in two different mediums was used for lead determination in standard soil sample with satisfactory results.

Solid phase extractive preconcentration of silver from aqueous samples

N,N-dibutyl-N1-benzoylthiourea (DBBT) impregnated onto a polymeric matrix, Amberlite XAD-16 was prepared. The separation and enrichment of Ag(I) from solution was investigated. Effective extraction conditions were optimized in column methods prior to determination by atomic absorption spectrometry. The optimum pH range for quantitative adsorption is 2–5. Quantitative recovery of Ag was achieved by stripping with 1mol L−1 thiourea in 1mol L−1 HCl. The sorption capacity of resin is 0.115mmol Ag+ g−1 resin. The relative standard deviation and detection limit was 3.1% for 1µg Ag+ mL−1 solution and 0.11µg L−1, respectively. The method was used for the determination of silver in geological water samples.

Free-Standing Networks of Core–Shell Metal and Metal Oxide Nanotubes for Glucose Sensing

Nanotube assemblies represent an emerging class of advanced functional materials, whose utility is however hampered by intricate production processes. In this work, three classes of nanotube networks (monometallic, bimetallic, and metal oxide) are synthesized solely using facile redox reactions and commercially available ion track membranes. First, the disordered pores of an ion track membrane are widened by chemical etching, resulting in the formation of a strongly interconnected pore network. Replicating this template structure with electroless copper plating yields a monolithic film composed of crossing metal nanotubes. We show that the parent material can be easily transformed into bimetallic or oxidic derivatives by applying a second electroless plating or thermal oxidation step. These treatments retain the monolithic network structure but result in the formation of core-shell nanotubes of altered composition (thermal oxidation: Cu2O-CuO; electroless nickel coating: Cu-Ni). The obtained nanomaterials are applied in the enzyme-free electrochemical detection of glucose, showing very high sensitivities between 2.27 and 2.83 A M-1 cm-2. Depending on the material composition, varying reactivities were observed: While copper oxidation reduces the response to glucose, it is increased in the case of nickel modification, albeit at the cost of decreased selectivity. The performance of the materials is explained by the network architecture, which combines the advantages of one-dimensional nano-objects (continuous conduction pathways, high surface area) with those of a self-supporting, open-porous superstructure (binder-free catalyst layer, efficient diffusion). In summary, this novel synthetic approach provides a fast, scalable, and flexible route toward free-standing nanotube arrays of high compositional complexity.

Absorption and fluorescence properties of aryl substituted porphyrins in different media.

Absorption and fluorescence properties of aryl substituted porphyrins, 5,10,15,20-tetra-4-oxy(aceticacid)phenylporphyrin (TAPP), 5,10,15,20-tetra-(4-phenoxyphenyl) porphyrin (TPPP), 5,10,15,20-tetra-(3-bromo-4-hydroxyphenyl) porphyrin (TBHPP), and 5,10,15,20-tetra-p-chloromethylphenyl porphyrin (CMPP) were investigated. The UV/vis absorption, fluorescence and excited spectra as the fluorescence quantum yields and fluorescence lifetimes for the compounds were measured in organic solvents (chloroform (CHCl(3)), tetrahydrofuran (THF)) and immobilized media (PVC film, sol-gel matrix). The fluorescence quantum yields of TAPP and TPPP were higher than the others. The fluorescence lifetimes of all studied porphyrin derivates were found to be fifty percent lower and their fluorescence intensities were increased fifty percent more in both of immobilized mediums, as compared to organic solvents.

Spectrofluorimetric and Potentiometric Determination of Acidity Constants of 4-(4′-Acetyloxy-3′-Methoxybenzylidene)-5-Oxazolone Derivatives

Abstract4-(4′-acetyloxy-3′-methoxybenzylidene)-5-oxazolone fluorescent molecules bearing four different aryl groups attached to the 2-position of 5-oxazolone ring have been investigated by spectrophotometric and potentiometric techniques in solution media. The acidity constants (pKa) of the fluorescent molecules were precisely determined in acetone, acetonitrile, dimethylformamide and in 1:1 mixture of toluene-isopropanol. The studied derivatives were titrated with tetrabutylammonium hydroxide and non-aqueous perchloric acid by scanning the basic and acidic region of the pH scale. A computerizable derivative method was used in order to descript precisely the end point and pKa values. The molecules investigated performed well-shaped and stoichiometric potentiometric titration curves.