Study of Ca-ATMP precipitation in the presence of magnesium ion

ATMP (aminotri(methylenephosphonic acid)), a phosphonate scale inhibitor used in the petroleum industry, was used as a model scale inhibitor in this study. One of the goals of this work was to determine the range of conditions under which Mg ions, which are formed in reservoir formations containing dolomite, modulate the formation of Ca-ATMP precipitate as a scale inhibitor. The results revealed that the amount of ATMP precipitated decreased with addition of Mg ions in solution at all values of the solution pH. Furthermore, an increase in both the solution pH and the concentration of the divalent cations in solution resulted in a change of the molar ratio of (Ca + Mg) to ATMP in the precipitates. At a low solution pH (pH 1.5), Mg ions had little effect on the composition of the Ca-ATMP precipitate. However, at higher values of the solution pH (pH 4 and 7), the Ca to ATMP molar ratio in the precipitates decreased with increasing concentration of the Mg. Here it was found that Mg ions replaced Ca ions on available reactive sites of ATMP molecules. These results determined the limits of the Mg ion concentration, which affects the precipitation of Ca-ATMP, Mg-ATMP, and (Ca + Mg)-ATMP. The dissolution of the scale inhibitors was studied using a rotating disk reactor. These experiments showed that the total divalent cation molar ratio (Ca + Mg) to ATMP in the precipitates is the primary factor that controls the rate of dissolution (release) of the phosphonate precipitates. The phosphonate precipitate dissolution rates decreased as the molar ratio of divalent cations to ATMP in the precipitates increased.     

The retention of iodine fission products on iodide precipitates

A fast and selective method has been developed for the separation of the iodine fission products in the primary cooling water of nuclear reactors. The parameters of the selective retention were studied on silver, thallium(I) and mercury(II) iodide. Retention experiments were performed on adequately thick layers of “free” precipitates and on precipitates fixed in filter paper. The latter method substantially increases the retention capacity. The papers with fixed precipitate are easy to handle. The filter paper with silver iodide precipitate was found to be the most satisfactory for the selective retention of fission iodine from reactor water.     

Comparison of two methods of detection,determination, and library search of the substances present in gas chromatography—mass spectrometry data

A comparison is made of two different methods, LIANAL and MSSMET, for the analysis of a g.c.—m.s. data matrix for the purpose of detecting and determining the metabolic profiles of the substances present. The parameters of the methods and the profiles determined on two different data matrices are compared. The two methods agree in 92 out of a possible 103 instances as to the presence or absence of the 103 substances for which they both made determinations. Ratios of the metabolic profiles for the two samples are highly correlated (0.9954) for the two methods.     

Comparison of transition probabilities calculated using different parameters on WBEPM theory for some p‐d and d‐p transitions in excited atomic nitrogen

The transition probabilities between individual and multiplet lines for some quartet terms of excited p‐d and d‐p transition arrays of nitrogen atom have been calculated using the weakest bound electron potential model (WBEPM) theory. For determination relevant parameters, we employed both numerical Coulomb approximation (NCA) method and numerical nonrelativistic Hartree–Fock (NRHF) wave functions for expectation values of radii. The necessary energy values have been taken from experimental energy data in the literature. The expectation values of radii obtained using the two different methods have been employed in the calculation of transition probabilities of all transition arrays. The results obtained have been compared with either each other or NIST data. Good agreement with accepted values taken from NIST has been observed for related excited transitions. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Comparison of PLS and kinetic models for a second-order reaction as monitored using ultraviolet visible and mid-infrared spectroscopy

A second-order reaction between benzophenone and phenylhydrazine to give benzophenone phenylhydrazone was followed using UV/vis and mid-infrared spectroscopic probes. Established kinetic (hard) and partial least squares (soft) modelling chemometrics methods were applied to both datasets in order to compare the information acquired with each probe. To this purpose, an experimental design with 25 samples and a test set with 5 samples were used to build a partial least squares calibration model to predict the concentration profiles of the compounds present in the reaction vessel. In addition, multivariate kinetic modelling was also performed on the spectroscopic data. Using a guess of the rate constant, concentration profiles were estimated. The profiles are then used to calculate the estimated spectroscopic profile, which is compared to the data acquired experimentally. The residual is minimised and the rate constant estimated; this procedure is iterated until convergence. A total of four profiles were obtained for each compound, corresponding to two sets of probes and two sets of models. The results were compared and discussed. It is shown that several different spectroscopic techniques can be used in reaction monitoring, with increasing benefits in terms of information and interpretation of the results. The profiles obtained agreed well which was also demonstrated when comparing the different rate constants obtained.     

Arsenic speciation in iron hydroxide precipitates

In this study a special sequential extraction method is proposed to discriminate between arsenic adsorbed and co-precipitated in precipitates arising mainly from iron hydroxides or bound in low solubility mineral phases. Synthetic iron hydroxide precipitates were prepared to investigate the influence of the amount of arsenate, of the manganese additionally added and of the valence state of arsenic on the remobilisation of arsenic. After preparing the precipitates with arsenate no arsenic could be detected in the supernatant solution. About 82% (w/w) of the arsenate is adsorbed to the precipitate and the remaining part can be dissolved by shaking with an oxalate buffer. A significant difference between the amount of arsenic added and the amount analysed in the two steps was not found. Consequently, compounds with a low solubility, such as scorodite, were not formed in the synthesized precipitates. The valence of the arsenic and addition of manganese influence significantly the uptake of arsenic by iron hydroxides. Natural precipitate samples from a percolate water of tin mill tailings were investigated using this method.     

Considerations in the determination of orientational order parameters from X-ray scattering experiments

An assessment of the data processing and analysis methods used to obtain the second- and fourth-rank orientational order parameters of liquid crystals from X-ray scattering experiments has been carried out, using experimental data from four extensively studied alkyl-cyanobiphenyls and calculated data generated from two general types of theoretical orientational distribution function. The application of a background subtraction and two different baseline correction methods to the scattering profiles is assessed, along with three different methods to analyse the processed data. The choice of baseline correction method is shown to have a significant effect: an offset to zero overestimates the order parameters from the experimental and calculated data sets, particularly for lower order parameters arising from broad distributions, whereas an offset to a value estimated from regions of low scattering intensity provides experimental values close to those reported from other experimental techniques. By contrast, the three different analysis methods are shown generally to result in relatively small absolute differences between the order parameters. We outline a straightforward general approach to experimental X-ray scattering data processing and analysis for uniaxial phases that results in order parameters that match well with those reported using other experimental techniques.     

Extended Poisson–Nernst–Planck modeling of membrane blockage via insoluble reaction products

A generalized time-dependent mathematical model is developed for a diffusion–migration–reaction system incorporating a pore blockage effect due to generation of insoluble precipitates in a porous membrane. The system behavior is investigated via direct numerical solution of an extended, highly non-linear equation set based on the classical Poisson–Nernst–Planck equations for ion transport. In order to treat the buildup of solid reaction products in the membrane, this novel formulation incorporates both a reaction term and a space- and time-dependent diffusivity expression based on a simple precipitation model. The model is demonstrated for a generalized case and then extended to cover the well-known reaction of silver and chloride ions to form insoluble AgCl. Time-dependent concentration profiles of all ions in the membrane are obtained and the effects of precipitate buildup in the pore space are investigated. The role of counterions in the transient behavior of the system is also clarified.     

Characterizing slow state near Si-SiO2 in MOS structure

The Equilibrium Voltage Step (EVS) technique has been used for extraction of depth and energy concentration profile of traps situated in the oxide of a lightly stressed metal-oxide-semiconductor (MOS) structure. This has been achieved up to the very near Si-SiO₂ interface. The results are discussed and compared with those obtained using charge pumping (CP) technique. A good agreement is achieved between the trap densities extracted using the two methods even though differences in the shape of the profiles can be observed. The results also very well agree with those published previously using current deep level transient spectroscopy (C-DLTS).     

Analytical Electron Microscopy Study of a ZnO-NiO Solid Solution

 Results of an analytical electron microscopy study of a binary ZnO-NiO system are reported and discussed. Emphasis was placed on the determination of Ni concentration (solubility) in the ZnO grains using quantitative TEM-EDXS. The influence on the results of beam diameter, foil thickness and corrections used are described and discussed. During the study small precipitates, presumably NiO, were found in the ZnO grains of the ZnO-NiO samples with different ZnO/NiO ratios. In TEM, the precipitates exhibited image contrast only at certain orientations and were normally invisible during the EDXS analysis. The presence of the precipitates too small to be seen using scanning electron microscopy could explain erroneous results for the Ni concentration in a ZnO solid-solution phase obtained previously using SEM-EDXS. Quantitative EDXS analyses were performed on ZnO grains using different electron beam diameters. In each sample, the spread of the results was correlated to the beam diameter (analysed volume). It was found that when the average number of precipitates was less than one per analysed volume the measured points that included precipitates could easily be identified on the basis of their deviation from the mean value of the Ni content.     

Formation and transformation of Al<Subscript>13</Subscript> from freshly formed precipitate in partially neutralized Al(III) solution

Al₁₃ is one of the novel nanospecies in partially neutralized Al(III) solution and Al-OH sol or precipitate could be generated simultaneously in the neutralization. Unfortunately, the precipitate is believed to be harmful to the formation of Al₁₃ due to the consumption of Al(OH)₄ ⁻, which was regarded as the precursor of Al₁₃. In this paper, the feasibility and potential of transformation of freshly formed Al-OH precipitate into Al₁₃ species were studied by using ferron colorimetric method and ²⁷Al NMR spectroscopy. The Al-OH precipitates were produced by two ways: injection of base solution into Al(III) solution gradually and mixing of Al(III) and base solutions instantaneously. The re-dissolving behaviors of the freshly formed precipitates were examined under different basicities (OH/Al molar ratio) and temperatures. It has been shown that Al₁₃ could be formed through the re-dissolution of intermediate Al-OH precipitate generated in partially neutralized Al(III) solution. A possible formation mechanism of Al₁₃ was suggested. Easily transformable precipitate was developed when the OH/Al molar ratio was less than 2.5. Rapid re-dissolution of freshly formed precipitate was favorable for Al₁₃ formation, which could be enhanced by heating.     

On the Intrinsic Volumes of Ions in Aqueous Solutions

Various methods that have been proposed in the literature for the estimation of the intrinsic volumes of electrolytes in aqueous solutions are briefly discussed. Most of these depend on the radii of the constituent ions. A method that is independent of the radii but requires a long extrapolation from the temperatures involved in salt melts is also mentioned. A new method is developed here, independent of ionic radii, which employs the partial molar volumes of salts in their concentrated solutions (and is, therefore, limited to highly soluble salts). These are extrapolated to a virtual concentration at which all the water present is as closely packed as possible, hence no longer capable of being electrostricted. The resulting intrinsic volumes of salts are reasonable when compared to other estimates of these quantities.     

A novel approach to identify plant parasitic nematodes using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Plant parasitic nematodes are difficult to identify because different species are morphologically similar, and this makes their control more difficult. The aim of this work was to develop a rapid, simple method to identify plant parasitic nematodes, based on analysis of protein profiles of nematodes generated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Two methods have been used: grinding and direct analysis of intact nematodes. Both methods were standardised using the nematode Anguina tritici (wheat seed-gall nematode) as a model. Development of the approach involved optimisation of experimental parameters to generate reproducible diagnostic protein profiles for plant parasitic nematodes. With alpha-cyano-4-hydroxycinnamic acid (CHCA) as the matrix, the most effective solvent extraction was with 90% acetone. With sinapinic acid (SA) as matrix, 90% ethanol was most effective. When intact nematodes were analysed directly by mixing with the matrix solution, 40 min extraction with CHCA matrix solution generated the best protein profiles. The standardised methods were applied to analyse the seed-gall nematodes A. tritici and A. funesta and to the root-knot nematode, Meloidogyne javanica, which infects many horticultural crops. Typical protein profiles and diagnostic peaks were identified for these nematode species and for mixtures of Anguina species. The results provide 'proof-of-concept' that these nematode species can be identified by protein profiling using MALDI-TOFMS. This new approach could be extended to identify other plant and non-plant parasitic nematodes.     

The parameterization and validation of generalized born models using the pairwise descreening approximation

Generalized Born Surface Area (GBSA) models for water using the Pairwise Descreening Approximation (PDA) have been parameterized by two different methods. The first method, similar to that used in previously reported parameterizations, optimizes all parameters against the experimental free energies of hydration of organic molecules. The second method optimizes the PDA parameters to compensate only for systematic errors of the PDA. The best models are compared to Poisson-Boltzmann calculations and applied to the computation of potentials of mean force (PMFs) for the association of various molecules. PMFs present a more rigorous test of the ability of a solvation model to correctly reproduce the screening of intermolecular interactions by the solvent, than its accuracy at predicting free energies of hydration of small molecules. Models derived with the first method are sometimes shown to fail to compute accurate potentials of mean force because of large errors in the computation of Born radii, while no such difficulties are observed with the second method. Furthermore, accurate computation of the Born radii appears to be more important than good agreement with experimental free energies of solvation. We discuss the source of errors in the potentials of mean force and suggest means to reduce them. Our findings suggest that Generalized Born models that use the Pairwise Descreening Approximation and that are derived solely by unconstrained optimization of parameters against free energies of hydration should be applied to the modeling of intermolecular interactions with caution.     

Determination of tannic acid after precipitation with bovine serum albumin by visible light scattering in a flow injection system

Tannic acid can form a precipitate with bovine serum albumin (BSA), and this was explored for its determination using a flow injection system along with detection via light scattering at 600 nm. The results on light scattering are confirmed using a particle sizing method. Scattering signals are negligible compared to the background generated by BSA in solutions with a pH of <4 or >8. Any precipitates on the wall of the flow cell pipeline were effectively removed by using a sodium dodecyl sulfate washing solution. The analytical range is from 70 to 250 µgmL^-1 of tannic acid. The results imply that increasing BSA concentrations will enhance sensitivity and analytical ranges. The system can be used in solutions of pH values between 5 and 7. The results correlated closely (r²?>?0.97) with those obtained by the ferrous tartrate method when analyzing a single tannic acid and two tea tannins.     

Two grid refinement methods in the lattice Boltzmann framework for reaction-diffusion processes in complex systems

This paper studies the optimisation of a numerical model and a computer code to solve numerically reaction-diffusion processes in environmental or biological systems with complicated geometries and mixtures of reactions including time and spatial scales extending over several order of magnitude. In particular, we consider different grid refinement techniques in the framework of a lattice Boltzmann solver for reaction-diffusion systems. Two new grid refinement methods are proposed, which are both quantitatively good. The first method is based on the matching of the concentration profiles and fluxes across two adjacent sub-domains, while the second method is based on nested subgrids. The focus of our study is the trade off between accuracy and CPU time. We show how the different parameters of the method, such as the refinement factors, the location of the boundary between different grids or coupling methods at the interface affect the quality of the numerical solution and the efficiency of the method.     

Analysis of the linear tension of two-dimensional droplets on heterogeneous adsorbents

A procedure for analyzing the formation processes of two-dimensional droplets of an adsorbate on a rigid adsorbent support is considered. The molecular theory is based on data on the potential functions between adsorbent atoms and adsorbate molecules. Interactions between nearest neighbors are considered in the quasi-chemical approximation. The internal motions of adsorbent atoms and adsorbate molecules are ignored. Problems of describing the formation of droplets on heterogeneous adsorbents are associated with calculations for binodals (illustrated with the simplest example of two different homogeneous crystal faces) due to the choice of methods for calculating linear tension and the structural model of the region of the liquid–vapor transition. The dependence of the characteristics of droplets in the layered structural model on the method for determining the reference lines of the tension is shown for their metastable and equilibrium states. It is found that for a number of structural parameters, the thermodynamic determination of the line of tensions of metastable droplets can result in nonmonotonic dependences of the linear tension on their radii. The characteristics of two-dimensional liquid–vapor interfaces are compared for two structural models: coordination sphere and layered. It is found that the coordination sphere model allows the exclusion of the structural parameter of the layered model, but both models need refinement at small radii.     

The formation of mixed copper(II) sulfide—silver(I) sulfide membranes for copper(II)-selective electrodes

Several methods for the preparation of mixed copper(II) sulfide—silver(I) sulfide precipitates have been investigated. Pellets of these materials have been tested for their suitability as copper(II)-selective membranes. Homogeneous membranes with satisfactory electrochemical properties can be prepared only from precipitates obtained by addition of the metal salts to sodium sulfide Membrane leakages, limits of detection, calibration curves and titration curves with different types of precipitate are discussed.     

Effect of the precipitation of neutral-soap, acid-soap, and alkanoic acid crystallites on the bulk pH and surface tension of soap solutions

The natural pH of sodium dodecanoate (laurate), NaL, and sodium tetradecanoate (myristate), NaMy, solutions is measured as a function of the surfactant concentrations at 25 degrees C, and at several fixed NaCl concentrations. Surface tension isotherms are also obtained. Depending on the surfactant concentration, the investigated solutions contain precipitates of alkanoic acid, neutral soap, and acid soaps. The latter are complexes of alkanoic acid and neutral soap with a definite stoichiometry. A method for identification of the different precipitates from the experimental pH isotherms is developed. It is based on the analysis of precipitation diagrams, which represent plots of characteristic functions. This analysis reveals that for the NaL solutions there are three concentration regions with different precipitates, including lauric acid and 1:1 acid soap. In the case of NaMy solutions, we identified the existence of concentration regions with precipitates of myristic acid: 4:1, 3:2, and 1:1 acid soaps, and coexistence of two solid phases: 1:1 acid soap and neutral soap. The solubility products of the precipitates have been determined. Modeling the acid soaps of different stoichiometry as solid solutions of alkanoic acid and 1:1 acid soap, we derived a theoretical expression for their solubility products, which agrees well with the experiment. The kinks in the surface-tension isotherms of the investigated solutions correspond to some of the boundaries between the regions with different precipitates in the bulk. The theoretical analysis indicates that for the NaL solutions the adsorption layer is composed mostly of lauric acid, while for the NaMy solutions + 10 mM NaOH the adsorption layer is composed of nondissociated molecules of neutral soap. The developed approach could be applied to analyze the type of precipitates and the behavior of the surface tension for solutions of sodium and potassium alkanoates with different chain lengths at various temperatures and concentrations.     

Comparison of different extraction and detection methods for sugars using amino-bonded phase HPLC

In this study, different methods are compared in order to quantitate individual sugars extracted from apple samples using methanol and water. Glucose, fructose, and sucrose are separated in 20 min using an amino-bonded carbohydrate column and a 75:25 acetonitrile-water mobile phase, followed by UV (190 nm) and refractive index detection. Variations in the sugar profiles are observed using different extraction or detection methods (or both) at a 1.4-mL/min flow rate. The data obtained show differences (p < 0.01) from both extraction or detection methods. The highest contents of free sugars studied occur in samples extracted with water.