Optimization of dispersive liquid-liquid microextraction of copper (II) by atomic absorption spectrometry as its oxinate chelate: application to determination of copper in different water samples

In this study a dispersive liquid-liquid microextraction (DLLME) method based on the dispersion of an extraction solvent into aqueous phase in the presence of a dispersive solvent was investigated for the preconcentration of Cu(2+) ions. 8-Hydroxy quinoline was used as a chelating agent prior to extraction. Flame atomic absorption spectrometry using an acetylene-air flame was used for quantitation of the analyte after preconcentration. The effect of various experimental parameters on the extraction was investigated using two optimization methods, one variable at a time and central composite design. The experimental design was performed at five levels of the operating parameters. Nearly the same results for optimization were obtained using both methods: sample size 5 mL; volume of dispersive solvent 1.5 mL; dispersive solvent methanol; extracting solvent chloroform; extracting solvent volume 250 microL; 8-hydroxy quinoline concentration and salt amount do not affect significantly the extraction. Under the optimum conditions the calibration graph was linear over the range 50-2000 muicro L(-1). The relative standard deviation was 5.1% for six repeated determinations at a concentration of 500 microg L(-1). The limit of detection (S/N=3) was 3 microg L(-1).     

N-Chloro-2,2-dimethyltaurines: a new class of remarkably stable N-chlorotaurines

The preparation of novel N-chloro-2,2-dimethyltaurine (4) and N,N-dichloro-2,2-dimethyltaurine (5) is described. These 2,2-dimethyltaurines were strategically designed to avoid the hydrolytic dehydrochlorination of N-chlorotaurines. Thus, they possess long-term stability in contrast to the parent N-chlorotaurines, which exhibit broad-spectrum antimicrobial activities.     

Centralized resource allocation with stochastic data

Data Envelopment Analysis (DEA) is a technique based on mathematical programming for evaluating the efficiency of homogeneous Decision Making Units (DMUs). In this technique inefficient DMUs are projected on to the frontier which constructed by the best performers. Centralized Resource Allocation (CRA) is a method in which all DMUs are projected on to the efficient frontier through solving just one DEA model. The intent of this paper is to present the Stochastic Centralized Resource Allocation (SCRA) in order to allocate centralized resources where inputs and outputs are stochastic. The concept discussed throughout this paper is illustrated using the aforementioned example.     

UV effects on marine planktonic food webs: A synthesis of results from mesocosm studies

UV irradiance has a broad range of effects on marine planktonic organisms. Direct and indirect effects on individual organisms have complex impacts on food-web structure and dynamics, with implications for carbon and nutrient cycling. Mesocosm experiments are well suited for the study of such complex interrelationships. Mesocosms offer the possibility to conduct well-controlled experiments with intact planktonic communities in physical, chemical and light conditions mimicking those of the natural environment. In allowing the manipulation of UV intensities and light spectral composition, the experimental mesocosm approach has proven to be especially useful in assessing the impacts at the community level. This review of mesocosm studies shows that, although a UV increase even well above natural intensities often has subtle effects on bulk biomass (carbon and chlorophyll), it can significantly impact the food-web structure because of different sensitivity to UV among planktonic organisms. Given the complexity of UV impacts, as evidenced by results of mesocosm studies, interactions between UV and changing environmental conditions (e.g. eutrophication and climate change) are likely to have significant effects on the function of marine ecosystems.     

Asymptotic properties of some non-autonomous systems in Banach spaces

Let X be a reflexive Banach space. We introduce the notion of weakly almost nonexpansive sequences (xn)_n?0 in X, and study their asymptotic behavior by showing that the nonempty weak ω-limit set of the sequence (xn/n)_n?1 always lies on a convex subset of a sphere centered at the origin of radius d=limn→∞‖xn/n‖. Subsequently we apply our results to study the asymptotic properties of unbounded trajectories for the quasi-autonomous dissipative system , where A is an accretive (possibly multivalued) operator in X×X, and f−f_∞∈Lp((0,+∞);X) for some f_∞∈X and 1?p<∞. These results extend recent results of J.S. Jung and J.S. Park [J.S. Jung, J.S. Park, Asymptotic behavior of nonexpansive sequences and mean points, Proc. Amer. Math. Soc. 124 (1996) 475-480], and J.S. Jung, J.S. Park, and E.H. Park [J.S. Jung, J.S. Park, E.H. Park, Asymptotic behaviour of generalized almost nonexpansive sequences and applications, Proc. Nonlinear Funct. Anal. 1 (1996) 65-79], as well as our results cited below containing previous results by several authors.     

Electrochemistry and Adsorptive Stripping Voltammetric Determination of Amoxicillin on a Multiwalled Carbon Nanotubes Modified Glassy Carbon Electrode

The study of electrochemical behavior of amoxicillin (AMX), a β‐lactam antibiotic, is described on a multiwalled carbon nanotubes (MWCNTs) modified electrode by electrochemical impedance spectroscopy (EIS) and adsorptive stripping voltammetry for sensitive determination of AMX in pharmaceutical and human urine samples within a wide pH range from 2.0 to 10.0. Also, studies by Fe₂O₃ nanoparticles modified carbon paste electrode show that iron oxide impurities in the MWCNTs are not active sites for sensing of amoxicillin. Under optimized conditions, the oxidation peak has two linear dynamic ranges of 0.6–8.0 and 10.0–80.0 μM with a detection limit of 0.2 μM and a precision of <4%.     

A generalized model for data envelopment analysis with interval data

Data envelopment analysis (DEA) is a method to estimate the relative efficiency of decision-making units (DMUs) performing similar tasks in a production system that consumes multiple inputs to produce multiple outputs. So far, a number of DEA models with interval data have been developed. The CCR model with interval data, the BCC model with interval data and the FDH model with interval data are well known as basic DEA models with interval data. In this study, we suggest a model with interval data called interval generalized DEA (IGDEA) model, which can treat the stated basic DEA models with interval data in a unified way. In addition, by establishing the theoretical properties of the relationships among the IGDEA model and those DEA models with interval data, we prove that the IGDEA model makes it possible to calculate the efficiency of DMUs incorporating various preference structures of decision makers.     

Multiwall carbon nanotubes decorated with FeCr2O4, a new selective electrochemical sensor for amoxicillin determination

Direct writing aims to deposit materials onto substrates in localised positions. In this paper, we demonstrate a new method for direct writing of nanoparticles at ambient-air-pressure. An electrical discharge is used to generate gold nanoparticles of the order of 10?nm diameter, which are then transported and ??focused?? by an electric field in air, through the process of electric field-assisted diffusion, as opposed to normal ballistic focusing since the mean free path in air is very short. This process is novel and allows for practical normal atmospheric-pressure focused deposition of nanoparticles. The focusing mechanism is capable of producing patterned arrays of deposited nanoparticles with widths that are less than 10?% of the diameter of the focusing apparatus; in the present experimental configuration, gold spots with diameters of a few tens of micrometres were achieved, with ultimate size being limited by transverse diffusion and by charged particle mutual repulsion. In this study, the process of generating nanoparticles from bulk material, transporting and focusing these particles takes place in one operation, which is a key advantage in rapid prototyping and manufacturing techniques.     

Electrochemical characterization of naproxen and the adsorbed naproxen oxidation products at glassy carbon electrode modified with carboxyl functionalized multi-walled carbon nanotubes and introducing a new route for naproxen determination

Journal of Solid State Electrochemistry - In the present work, a glassy carbon electrode was modified with carboxyl functionalized multi-walled carbon nanotubes (f-MWCNTs) to investigate the...