Determination of beryllium in solid samples by flame atomic absorption spectrometry after preconcentration on activated carbon.

It is generally supposed that the preconcentration procedure is used for the determination of metal concentrations under the sensitivity of the measurement method. This study showed that preconcentration is also need for the beryllium (Be) concentration over the sensitivity of atomic absorption spectrometry. For this purpose, a simple and selective method for the determination of Be in solid samples is modified. The method is based on the preconcentration of the complexes of beryllium-acetylacetone plus morin, oxine, PAN and PAR on activated carbon at different pH values. The adsorbed beryllium was eluted with aqua regia and measured by flame atomic absorption spectrometry (FAAS). Recoveries of up to 85% were achieved. For removing chemical interferences and applying the method to Be determination in solid samples, the masking studies and reproducibility were examined. The detection limit was found to be 0.12 ng mL(-1). The relative sandard deviations (RSD) were found to be 8% for 60 mL of 10.0 ng mL(-1) using 10 replicate enrichment procedures. Beryllium concentrations in the studied solid samples were found in the range of 0.28 - 3.95 mg kg(-1).     

Variations in Toxic Metal Levels of Two Fish Species,Pomatomus saltatrix and Dicentrarchus labrax,and Risk Estimation for Children

The concentrations of five toxic metals were monthly determined in two fish species,obtained from fish markets in Turkey during 2010—2011.For the determinations,AAS and ICP-AES were used.The obtained lead concentrations for all studied Pomatomus saltatrix(mean 635μg·kg-1)and Dicentrarchus labrax(mean 463μg·kg-1)samples were found to be significantly higher than the maximum allowances concentration(MAC)of 300μg·kg-1.Mean chromium(324μg·kg-1)and Cu(940μg·kg-1)concentrations in Pomatomus saltatrix were higher than in Dicentrarchus labrax(268μg Cr·kg-1 and 600μg Cu·kg-1)while Ni in Pomatomus saltatrix(216μg·kg-1)was lower in Dicentrarchus labrax(291μg·kg-1).The estimated non-carcinogenic and carcinogenic health risks by the Target Hazard Quotient and target carcinogenic risk indicate that there are no sytemic effects,and the risk of developing cancer over a human lifetime is between 2~9in 1 000 000.     

Can Extensional Flow Rupture Macromolecules in an Electrospinning Process?

The fracture of high molecular weight poly(ethylene oxide) (PEO) chains under extensional stretching during the electrospinning of aqueous solutions was investigated by measuring solution viscosities and monitoring the change of molecular weight. The degree of macromolecular chain fractures in 1.0% polymer solutions increased with the increase in molecular weight. The strain rates for stretching and fracturing of macromolecules are critical for the degradation of polymers along with experimental elongational strain rates. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1051–1054     

Quantitative characterization of chemical degradation of heat‐treated wood surfaces during artificial weathering using XPS

The X‐ray photoelectron spectroscopy (XPS) study of three heat‐treated North American wood species (jack pine, birch and aspen) was carried out to evaluate chemical modifications occurring on the wood surface during artificial weathering for different times. The results suggest that the weathering reduces lignin content (aromatic rings) at the surface of heat‐treated wood, consequently, the carbohydrates content increases. This results in surfaces richer in cellulose and poorer in lignin. Heat‐treated wood surfaces become acidic due to weathering, and the acidity increases as the weathering time increases. Three possible reasons are given to account for the increase of acidity during weathering. The lignin content increases, whereas the hemicelluloses content decrease due to heat treatment. Heat‐treated woods have lower acidity to basicity ratios than the corresponding untreated woods for all three species because of the decrease in carboxylic acid functions mainly present in hemicelluloses. The wood composition changes induced by weathering are more significant compared to those induced by heat treatment at wood surface. Exposure to higher temperatures causes more degradation of hemicelluloses, and this characteristic is maintained during weathering. However, the wood direction has more effect on chemical composition modification during weathering compared to that of heat treatment temperature. The heat‐treated jack pine is affected most by weathering followed by heat‐treated aspen and birch. This is related to differences in content and structure of lignin of softwood and hardwood. The use of XPS technique has proved to be a reliable method for wood surface studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Polyhedral Analysis for Concentrator Location Problems

The concentrator location problem is to choose a subset of a given terminal set to install concentrators and to assign each remaining terminal node to a concentrator to minimize the cost of installation and assignment. The concentrators may have capacity constraints. We study the polyhedral properties of concentrator location problems with different capacity structures. We develop a branch and cut algorithm and present computational results.     

Determination of molybdenum in biological samples by flame atomic spectrometry after preconcentration on activated carbon

Abstract  

Molybdenum is well known for its toxic effects, although it is also essential for N₂-fixing cyanobacteria and several enzymes. This study proposes a simple and accurate procedure for separation, preconcentration, and determination of trace amounts of molybdenum in biological samples by flame atomic absorption spectrometry. It is based on complexation of Mo by cupferron and sorption onto activated carbon. Effects of parameters such as pH, stirring time, and amounts of activated carbon and cupferron on recovery were examined. The results demonstrated that Mo at pH range of 2.5–3.5 was quantitatively sorbed onto activated carbon as its cupferron complex. The optimum stirring time was found to be 30 min. The relative standard deviation was found to be 12% for 200 cm³ 50 ng/cm³ Mo using 10 replicate preconcentration procedures. The limits of detection and quantification were found to be 1.0 and 3 ng/cm³, respectively, by preconcentration of 200 cm³ initial sample to 2 cm³ final volume. As a result, an enrichment factor of 100-fold was achieved. The proposed preconcentration procedure was applied to determine Mo in biological samples such as vegetables, milk, and animal liver. The molybdenum concentrations were found (as μg/dm³ or μg/kg) in the range of 70–5,500 for plants, 3–124 for milk and milk powder, and 960 for liver samples.     

Electronic absorption and Raman resonance scattering of spectroscopically pure SiO2

An ultraviolet absorption, as well as Stokes and anti-Stokes Raman resonance scattering of spectroscopically pure SiO2 was investigated by flash photolysis technique. The whole spectrum of 'absorption and scattered bands' was recorded photographically in ultraviolet. A resonance absorption line was observed at 288.2 nm, without structure, while scattered lines were observed at 285-288.2 and 288.2-290 nm.     

Variations in Toxic Metal Levels of Two Fish Species,Pomatomus saltatrix and Dicentrarchus labrax,and Risk Estimation for Children简

The concentrations of five toxic metals were monthly determined in two fish species, obtained from fish markets in Turkey during 2010—2011. For the determinations, AAS and ICP-AES were used. The obtained lead concentrations for all studied Pomatomus saltatrix (mean 635 μg·kg-1) and Dicentrarchus labrax (mean 463 μg·kg-1) samples were found to be significantly higher than the maximum allowances concentration (MAC) of 300 μg·kg-1. Mean chromium (324 μg·kg-1) and Cu (940 μg·kg-1) concentrations in Pomatomus saltatrix were higher than in Dicentrarchus labrax (268 μg Cr·kg-1 and 600 μg Cu·kg-1) while Ni in Pomatomus saltatrix (216 μg·kg-1) was lower in Dicentrarchus labrax (291 μg·kg-1). The estimated non-carcinogenic and carcinogenic health risks by the Target Hazard Quotient and target carcinogenic risk indicate that there are no sytemic effects, and the risk of developing cancer over a human lifetime is between 2～9 in 1 000 000.     

Eco‐friendly Sensors Developed by Herbal Based Silver Nanoparticles for Electrochemical Detection of Mercury (II) Ion

In our study, the single‐use & eco‐friendly electrochemical sensor platform based on herbal silver nanoparticles (AgNPs) was developed for detection of mercury (II) ion (Hg²⁺). For this purpose, the surface of pencil graphite electrode (PGE) was modified with AgNPs and folic acid (FA), respectively. The concentrations of AgNPs and FA were firstly optimized by differential pulse voltammetry (DPV) to obtain an effective surface modification of PGE. Each step at the surface modification process was characterized by using cyclic voltammetry (CV) and electrochemical impedence spectroscopy (EIS). The limit of detection (LOD) for Hg²⁺ was estimated and found to be 8.43 μM by CV technique. The sensor presented an excellent selectivity for Hg²⁺ against to other heavy metal ions such as Ca²⁺, Cd²⁺, Cr³⁺, Cu²⁺, Mg²⁺, Ni²⁺, Pb²⁺, Zn²⁺, Co²⁺ and Mn²⁺. Moreover, a rapid, selective and sensitive detection of Hg²⁺ was successfully performed in the samples of tap water within 1 min.