Enrichment of copper and nickel with solid phase extraction using multiwalled carbon nanotubes modified with Schiff bases

The behaviour of some Schiff bases in the presence of metal ions is very selective in complex formation. In this study, new, selective and easily prepared adsorbent materials have been developed. Multiwalled carbon nanotubes (MWCNTs) are quite suitable as supporting material for preparation of new solid phase adsorbents modified with Schiff bases due to their selective nature. Different Schiff bases were designed and synthesised as adsorbent agents for Ni(II) and Cu(II) ions, according to the literature, and MWCNTs were modified with these Schiff bases. The modification of CNTs was performed by adsorption from the alcoholic solution of Schiff base. The measurements of Ni(II) and Cu(II) ions were carried out using ICP-MS. Different parameters such as pH, model and eluent solution flow rates, eluent type, amount of ligand, sample volume and effect of foreign ions, which have an effect upon recovery of analytes, were investigated. The obtained results indicated that enrichment can be done with six modified adsorbent materials for Cu(II) at pH 9 and two modified adsorbent materials for Ni(II) at pH 8. It was concluded that four adsorbent materials were selective only for the enrichment of Cu(II). Merely one modified adsorbent material was noneligible for the enrichment of Cu(II) and Ni(II). The solid phase adsorbents prepared by modification with two of the Schiff bases used in this study showed an enrichment factor of 80 for both metal ions, whereas the solid phase adsorbents prepared by modification with four of the Schiff bases showed an enrichment factor of 40 for Cu(II) ions. The confirmation of the developed method was tested with certified reference materials with satisfactory results.     

Application of colloidal palladium modifier for the determination of As, Sb and Pb in a spiked sea water sample by electrothermal atomic absorption spectrometry

Colloidal palladium was used as a chemical modifier for analysis of complex samples by electrothermal atomic absorption spectrometry. In order to demonstrate high potential of the modifier, optimization of the time–temperature program of the atomizer was limited with only pyrolysis and atomization temperatures. Fixed palladium modifier masses were applied (6 μg for pure analyte solutions and 15 μg for matrix-containing solutions). It was shown that in the presence of colloidal palladium, interference-free determinations of As, Sb and Pb are possible up to at least 450 μg of chloride ion, or 40 μg of sulfate ion (as their sodium salts) in the atomizer. Colloidal palladium was used for the direct determination of As, Sb and Pb in a spiked sea water sample (from Bosphorus channel near Istanbul) by means of the calibration graphs prepared with pure analyte solutions. The detection limits for As, Sb and Pb in a sea water matrix calculated according to 2σ criteria are 5.4, 3.6 and 1.1 ng ml⁻¹, respectively (for sample volume 10 μl). In unspiked sea water, the contents of As, Sb and Pb were found to be below the detection limits. Recoveries of spiked analytes (25 and 50 ng ml⁻¹) were in the region of 98–112% depending on the nature of analyte and the concentration of spike.     

Effect of ball-milling conditions on microstructure during production of Fe–20Mn–6Si–9Cr shape memory alloy powders by mechanical alloying

Phase transitions associated with Fe?C20?wt% Mn?C6?wt% Si?C9?wt% Cr alloy during mechanical alloying and after subsequent annealing of that are studied experimentally. The conventional powder metallurgy route was used in preparing the sample. The milling time ranged from 5 to 20?h. Changes in microstructure as a function of milling time were investigated by using X-ray diffraction analysis, differential scanning calorimeter, and scanning electron microscopy. The grain sizes of powder milled are determined. The critical temperatures associated with the transformations are found to change with increasing ball-milling time.     

Electroanalytical Studies and Simultaneous Determination of Amlodipine Besylate and Atorvastatine Calcium in Binary Mixtures Using First Derivative of the Ratio‐Voltammetric Methods

The electrochemical behavior of atorvastatin and amlodipine at a glassy carbon electrode has been studied using different voltammetric techniques. First derivative of the ratio voltammetric methods for determination of amlodipine and atorvastatin in tablets in the presence of the other compound has been described. This technique depends on the measuring of first derivative of the ratio voltammograms of each concentration as a function of the increased concentrations. DP and SW voltammetric methods depend on first derivative of the ratio‐voltammetry by measurements of the selected potentials for amlodipine and atorvastatin. The linear response was within the range of 4×10^?6–1×10^?4 M for amlodipine and 2×10^?6–1×10^?4 M for atorvastatin. The proposed methods have been extensively validated.     

Agricultural planning of annual plants under demand,maturation, harvest,and yield risk

In this study we present a planning methodology for a firm whose objective is to match the random supply of annual premium fruits and vegetables from a number of contracted farms and the random demand from the retailers during the planning period. The supply uncertainty is due to the uncertainty of the maturation time, harvest time, and yield. The demand uncertainty is the uncertainty of weekly demand from the retailers. We provide a planning methodology to determine the farm areas and the seeding times for annual plants that survive for only one growing season in such a way that the expected total profit is maximized. Both the single period and the multi period cases are analyzed depending on the type of the plant. The performance of the solution methodology is evaluated by using numerical experiments. These experiments show that the proposed methodology matches random supply and random demand in a very effective way and improves the expected profit substantially compared to the planning approaches where the uncertainties are not taken into consideration.     

Effects of annealing and high radiation dose on the thermoluminescence characteristics of natural fluorite

In this study, the various dosimetric properties of the thermoluminescent (TL) phosphor of CaF₂:natural including response characteristics, sensitivity to thermal annealing and decay of stored energy were investigated in detail. The analysis of the peak temperature values and the half widths of the resolved components in the glow curves, by using the Computerized Glow Curve Deconvolution (CGCD) Method, resulted in the activation energy (E) of 0.85–1.83 eV and frequency factor (s) of 6.17E+9–2.90E+15 s^?1. The effects of pre-irradiation thermal annealing on the radiation-induced sensitization of the thermoluminescent response of CaF₂:natural were presented. An enhancement of sensitivity after being subjected to a high beta particle exposure was clarified. The effect was complicated by the influence of heat treatments before the exposure to radiation. Replicate runs on CaF₂:natural after irradiation with 1 Gy absorbed dose indicated good reproducibility of peak temperatures and intensities; they can be re-used for repeated measurements. It appeared that the main dosimetric peak at 280 °C exhibits negligible fading over 4 weeks and may be used for dosimetry. This study has demonstrated that the potential exists for the use of CaF₂:natural for TL radiation dosimetry.     

Effect of Lewis acid catalysts on Diels-Alder and hetero-Diels-Alder cycloadditions sharing a common transition state

The thermal and Lewis acid catalyzed cycloadditions of beta,gamma-unsaturated alpha-ketophosphonates and nitroalkenes with cyclopentadiene have been explored by using density functional theory (DFT) methods. In both cases, only a single highly asynchronous bis-pericyclic transition state yielding both Diels-Alder and hetero-Diels-Alder cycloadducts could be located. Stepwise pathways were found to be higher in energy. On the potential energy surface, the bis-pericyclic cycloaddition transition state is followed by the Claisen rearrangement transition state. No intermediates were located between these transition states. Claisen rearrangement transition states are also highly asynchronous, but bond lengths are skewed in the opposite direction compared to the bis-pericyclic transition states. The relative positions of the bis-pericyclic and Claisen rearrangement transition states may control periselectivity due to the shape of the potential energy surface and corresponding dynamical influences. Inspection of the thermal potential energy surface (PES) indicates that a majority of downhill paths after the bis-pericyclic transition state lead to the Diels-Alder cycloadducts, whereas a smaller number of downhill paths reach the hetero-Diels-Alder products with no intervening energy barrier. Lewis acid catalysts alter the shape of the surface by shifting the cycloaddition and the Claisen rearrangement transition states in opposite directions. This topographical change qualitatively affects the branching ratio after the bis-pericyclic transition state and ultimately reverses the periselectivity of the cycloaddition giving a preference for hetero-Diels-Alder cycloadducts.     

Alloying effects on Kβ/Kα intensity ratios and electrical properties in Cd1−xZnxS semi-conductor alloys

The alloying effect on K_β/K_α intensity ratio in Cd_1−xZn_xS semi-conductor alloys and on structural, electrical and optical properties of these alloys were investigated. The sample was excited by gamma rays with energy 59.5 keV photons from an Am-241 radioisotope source. K X-rays emitted by the sample were counted with a Si(Li) detector. We found that the K_β/K_α intensity ratio is changed by the alloying effect in Cd_1−xZn_xS semi-conductor alloys for different compositions x. We compared our results with the theoretical values.     

Synthesis and Characterization of Novel N-, S-, O-Substituted P-Chloranil Derivatives

A series of novel N-, S-, and O-substituted p-chloranil derivatives were synthesized from the reactions of p-chloranil (1) and related nucleophiles in sodium carbonate (Na₂CO₃) solution of acetonitrile or in chloroform with Et₃N. The structures of novel compounds were characterized by using microanalysis, Fourier transform–infrared, ¹H NMR, ¹³C NMR, and mass spectrometry.