Study of the stabilization of cis-hexadec-11-enal — The main component of the sex pheromone of the cotton boll worm — By tocopherol

The stabilization of cis-hexadec-11-enal — the main component of the sex pheromone of the boll worm — by additions of tocopherol has been studied by UV spectroscopy. It has been shown that the addition of 2–2.5% of tocopherol considerably increases the stability of the attractant.     

Synthesis of (6z)-cis-9S,10R-epoxyheneicosene,a component of the ruby tiger moth pheromone

A 10-step synthesis of the titled pheromone and analogues from an acyclic derivative of D-Xylose is described.     

Voltammetric determination of Cr(III) in plating baths containing Cr(III) salts as the main component

The differential pulse single-sweep voltammetric technique with hanging mercury drop electrode was used for the determination of Cr(III). The determination was carried out in 0.2 mol/l sodium acetate as supporting electrolyte. The reduction peak of Cr(III) was recorded at –1.5 V vs. Ag/AgCl reference electrode. The relative standard deviation was 3% for Cr concentrations in the range of 0.4 mol/l. The determination of impurities (Cd, Cu, Pb and Zn) in fresh and overworked galvanic baths using anodic stripping voltammetry in the differential pulse mode is also described.     

Quasiclassical determination of reaction probabilities as a function of the total angular momentum

This article presents a quasiclassical trajectory (QCT) method to determine the reaction probability as a function of the total angular momentum J for any given value of the initial rotational angular momentum j. The proposed method is based on a discrete sampling of the total and orbital angular momenta for each trajectory and on the development of equations that have a clear counterpart in the quantum-mechanical (QM) case. The reliability of the method is illustrated by comparing QCT and time-dependent wave-packet QM results for the H+D(2)(upsilon=0,j=4,10) reaction. The small discrepancies between both sets of calculations, when they exist, indicate some genuine quantum effects. In addition, a procedure to extract the reaction probabilities as a function of J when trajectories are calculated in the usual way using a continuous distribution of impact parameters is also described.     

Experimental determination of the electron tunneling probability as a function of distance for chemical reactions

The kinetics for the tunnelling reaction of trapped electrons with Cu(en)²⁺₃ in a rigid, glassy matrix at 77 K have been measured using pulse radiolysis. The distribution of the Cu(en)³⁺₃ ions was studied in the same system by measurements of ESR line widths, and found to be uniform (random). These measurements help to confirm the measured tunneling distances and the exponential dependence of the rates on the distance between the electron donor and acceptor.     

Quantitative determination of fluoride as a major pollutant in the emissions from the thermal treatment of clayey raw materials

Three clayey raw materials for production of traditional ceramics, all with medium to high fluorine content, have been investigated for determining their attitude to fluoride emission during firing, at varying parameters of the firing cycle, maximum firing temperature included, and in the presence or in the absence of calcium carbonate either added to the sample or naturally present in it. Different analytical methods for the determination of fluoride have been tested, together with different sample preparation procedures aimed to obtain minimum loss of fluoride in the pre-treatment step.     

A voltammetric sensor based on graphene-modified electrode for the determination of trace amounts of l-dopa in mouse brain extract and pharmaceuticals

l-Dopa is the intermediate precursor of the neurotransmitter dopamine. Unlike dopamine, l-dopa easily enters the central nervous system. l-Dopa, as one of the catecholamines, is widely used as a source of dopamine in the treatment of most patients with Parkinson’s disease and epilepsy. Graphene (GR) is ideally suited for implementation in electrochemical applications due to its reported large electrical conductivity, large surface area, unique heterogeneous electron transfer rate, and low production costs. This work reports the synthesis of GR using a modified Brodie method and its application for the electrochemical determination of l-dopa in real samples. Electrochemical measurements were performed at glassy carbon electrode modified with graphene (GR/GCE) via drop casting method. Cyclic voltammograms of l-dopa at GR/GCE showed an increased current intensity compared with GCE. All the measurements were done in phosphate buffer solution 0.1 M (pH 6.2) and the oxidation peak was observed at 0.27 V vs. Ag/AgCl. The effect of scan rate showed that oxidation of l-dopa on GR/GCE was surface controlled. The oxidation peak current of l-dopa gradually increased with increasing accumulation time from 0 to 300 s and accumulation potential from 0.0 to 0.3 V and reached the maximum current response at 240 s and 0.2 V for the accumulation time and accumulation potential, respectively. Voltammetric peak currents showed a linear response for l-dopa concentration in the range of 0.04 to 79 μM and a detection limit of 0.022 μM (22 nM). The relative standard deviation for five determinations of 50 μM l-dopa was 0.52 %.     

Optimisation of sensitivity in the multi-elemental determination of 83 isotopes by ICP-MS as a function of 21 instrumental operative conditions by modified simplex, principal component analysis and partial least squares

The optimisation of the sensitivity in the ICP-MS determination of 83 isotopes, as a function of 21 operative parameters was performed by generating an initial experimental design that was used to define, by principal component analysis, the multi-criteria target function. The first PC, which contained an overall evaluation of the signal intensity of all isotopes, was used to rank the experiments. The modified simplex optimisation technique was then applied on the ranked experiments. The increase in signal intensity was, on the average, 3.9 times for the isotopes considered for the simplex procedure. When finally convergence was achieved, a PLS regression model calculated on the available experiments allowed to investigate the effect played by each factor on the experimental response. Simplex and PCA proved to be extremely effective to obtain the optimisation and to generate the multi-criteria target function: they can be suggested as an automatic method to perform the optimisation of the instrumental operative conditions.     

Accuracy in the determination of the compositions of main rockforming silicates and oxides on a JXA-8100 microanalyzer

The individual sources of errors in procedures used for considering matrix effects were studied. The ZAF and PRZ analytical programs provided good correction in the predominance of one of the matrix effects, namely, absorption or the atomic number. Their simultaneous occurrence increased the total error to 2–4 rel %. In the ZAF method, normalization to oxygen in terms of stoichiometry introduced errors if the sample simultaneously contained the test element in various oxide forms. The greatest error of up to 1–2 wt % appeared in simple and double oxides. In the analysis of the main rockforming silicates with the determination of total iron as FeO, the presence of Fe₂O₃ can change the concentration of components to ∼0.2%.     

Fulvic acid sorption on muscovite mica as a function of pH and time using in situ X-ray reflectivity

Interfacial structures of the basal surface of muscovite mica in 100 mg kg (-1) Elliott Soil Fulvic Acid II solutions were investigated using in situ X-ray reflectivity. Molecular-scale variations in the thickness and internal structure of the fulvic acid (FA) film were observed and quantified as a function of pH (2-12) and reaction time (3-500 h at pH 3.7). At pH < or =6, the electron-density profile of the FA layer sorbed on the muscovite surface was composed of one near-surface peak followed by a broad peak that diminished in electron density with distance from the surface. The presence of the near-surface peak is attributed to condensation of FA molecules during sorption. The apparent thickness of the FA layer decreased from 12.3 to 7.2 to 6.4 A as pH increased from 2 to 3.7 to 6, respectively. At pH > or =8.5, a distinct interfacial structure was observed, consisting of sharper peaks similar to those previously observed for muscovite in the absence of FA. These peaks are most likely composed of smaller aqueous species, such as H 2O molecules, metal ion impurities from FA, and Na (+) from NaOH. The FA sorbed on the muscovite surface at pH 3.7 maintained a relatively constant thickness after 3 hours. However, the electron density of the near-surface FA peak increased by about 24% from 3 to 12 hours, and remained relatively constant from 12 to 500 hours. The electron density of the more distant part of the sorbed FA layer increased slightly after 12-50 hours of reaction but then decreased, and the broad peak flattened by 500 hours. Internal structural changes are possibly due to the slow sorption rate of FA molecules, or a fractionation effect, i.e., continuous subsitution of smaller FA molecules by larger FA molecules.     

High-performance liquid chromatography using a color-forming agent as a component of the mobile phase. Separation and determination of nickel and zinc wity xylenol orange

Summary A liquid chromatographic procedure for separating nickel and zinc has been developed. Xylenol orange, which is one of the sensitive and commercially available color-forming agents, was used as a component of the mobile phase. The two ions could be separated on weak anion-exchange gels within 10 min. The procedure was suitable for the determination of nickel and zinc in relatively pure solutions with fairly high sensitivity. The described liquid chromatographic analysis would be also potentially applicable for any aqueous sample containing trace levels of metal cations at 1–10 ppm.     

Errors in the determination of activation energies of solid-state reactions by the Piloyan method,as a function of the reaction mechanism

The errors in the activation energies of solid-state reactions determined with the Piloyan method are more larger than those previously assumed in the literature. On the other hand, the errors in the kinetic parameters are strongly dependent on the kinetic law obeyed by the reaction. A theoretical explanation of this behaviour is given.

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Zusammenfassung Die Fehler der nach der Piloyan-Methode bestimmten Aktivierungsenergien von Festkörperreaktionen sind grö\er als bisher in der Literatur angenommen und stark abhÄngig von der Reaktionsordnung. Eine theoretische ErklÄrung dieses Verhaltens wird gegeben.

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Interpretation of the ultrasonic effect on induction time during BaSO4 homogeneous nucleation by a cluster coagulation model

The effects of power ultrasound on the induction time of BaSO4 are studied experimentally and theoretically. In the experiments, barium sulfate is precipitated by mixing aqueous BaCl2 solution and Na2SO4 solution. The induction time is identified and measured by recording the change of turbidity in solution. Various energy inputs are used to investigate the effect of energy on nucleation. The results show that the induction time decreases with increasing supersaturation and increasing energy input. Employing the classical nucleation theory, the interfacial tension is estimated. In addition, the ultrasonic effects on nucleation order (n) and the nucleation coefficient (kN) are also investigated. A cluster coagulation model, which brings together the current nucleation models and the theories describing the behavior of colloidal suspensions, was applied to estimate the induction time under various energy inputs. A comparison between the results of model and the results of experiments shows that the number of monomers in dominating clusters (g) in the solution remains constant with increasing of energy input.     

Application of calorimetry as a main tool in evaluation of the effect of carbonate additives on cement hydration

Calorimetry was applied to follow the hydration in the Portland cement–dolomite–limestone mixtures. In the experiments the limestone additive of various fineness (standard component of various common cements), as well as the dolomite additive (not a standard component) were used. The rate of hydration versus time for common cements reflects the proper setting and early hardening during the first days after mixing with water (two or three peaks and the induction period between them). The aim of measurements presented in this work was to show the course of heat evolution curve and the heat evolved values, equivalent to the acceleration/retardation of hydration, in case of the pastes produced from Portland cement and the carbonate additives mixed in variable proportions, as well as to verify the results by other methods. The rate of heat evolution accompanying cement paste hydration, total heat evolved, conductivity of hydrating suspension and rheological (flow) properties versus time are modified by the fine grained carbonate additives. This is due to the hypothetical nucleating effect of limestone and dolomite.     

The influence of PEEK as a pore former on the microstructure of brush-painted LSCF cathodes

Journal of Solid State Electrochemistry - At lower operation temperature of intermediate temperature solid oxide fuel cells (IT-SOFC), polarization resistance was recognized as a limiting step...     

Gastrointestinal absorption of chlorothiazide: evaluation of a method using salicylazosulfapyridine and acetaminophen as the marker compounds for determination of the gastrointestinal transit time in the dog

Gastrointestinal absorption properties of chlorothiazide was investigated in dogs by a double-marker method using acetaminophen and salicylazosulfapyridine as the markers. The mean absorption time of acetaminophen (MATAAP) and the time for first appearance of sulfapyridine in plasma (TFASP) were used for the assessment of gastric emptying and oro-colonic transit times, respectively. Chlorothiazide absorption efficiency was increased by pretreatment with atropine sulfate. There was a good correlation between MATAAP and the extent of bioavailability of chlorothiazide, however, there was no correlation between TFASP and the extent of bioavailability of the drug. These results indicate that chlorothiazide absorption takes place primarily in a limited segment of the upper small intestine, supporting the assumption reported previously. This double-marker method seems to be a useful tool for the investigation of the relationship between drug absorption and its gastrointestinal transit.     

Application of crude extract of kohlrabi (Brassica oleracea gongylodes) as a rich source of peroxidase in the spectrofluorometric determination of hydrogen peroxide in honey samples.

Crude extract of kohlrabi (Brassica oleracea gongylodes) was prepared by a simple procedure and its enzymatic activity and total protein concentration were determined. It was found that this crude extract is a rich source of peroxidase (POx) and has high specific activity. Cross-linked polyvinylpyrrolidone was used as a stabilizer in the preparation of the crude extract. The POx activity of kohlrabi crude extract did not vary for at least 2 months when deoxygenated and stored at 4 degrees C. This extract was applied for the spectrofluorometric determination of hydrogen peroxide using homovanillic acid as a fluorogenic substrate. POx catalyzes the hydrogen peroxide oxidation of homovanillic acid to produce a dimer which shows strong fluorescence at 420 nm with excitation at 312 nm. In the optimum conditions, the calibration graph for hydrogen peroxide was linear up to 190 ng mL(-1), with a detection limit of 4.4 ng mL(-1). The relative standard deviation (RSD) was 1.48% for 50 ng mL(-1) hydrogen peroxide. The proposed method was successfully applied to the determination of hydrogen peroxide in honey. The concentration-time profile of H2O2 produced upon dilution of honey was studied and H2O2 contents of some different honeys from various areas of Iran were determined.     

Equilibrium contact angles as a function of the concentration of nonionic surfactants on quartz plate

The contact angles of aqueous solution of Triton X-100 and Triton X-305 for airwater-quartz and cyclohexane-water quartz systems have been studied. It has been found that the equilibrium contact angle (measured through water) against quartz is increased by the addition of small amounts of nonionic surfactants, but beyond a certain concentration the angle decreases again. Based on the bilayer adsorption model on quartz/water interface, the experimental results can be explained.