On the applicability of the HSAB principle through the use of improved computational schemes for chemical hardness evaluation

Finite difference schemes, named Compact Finite Difference Schemes with Spectral-like Resolution, have been used for a less crude approximation of the analytical hardness definition as the second-order derivative of the energy with respect to the electron number. The improved computational schemes, at different levels of theory, have been used to calculate global hardness values of some probe bases, traditionally classified as hard and soft on the basis of their chemical behavior, and to investigate the quantitative applicability of the HSAB principle. Exchange acid-base reactions have been used to test the HSAB principle assuming the reaction energies as a measure of the stabilization of product adducts.     

Synthesis of lead magnesium niobate and La-modified lead magnesium niobate using different Mg precursors

Summary In the present study, the effect of the partial replacement of Pb²⁺ by La³⁺ in the lead magnesium niobate Pb(Mg_1/3Nb_2/3)O₃ (PMN) perovskite structure was examined, taking into account the Mg-source. Pure lead magnesium niobate (PMN) and lanthanum-modified lead magnesium niobate (PLMN) having composition (Pb_1-xLa_x) (Mg_1+x/3Nb_2-x/3)O₃ with x=0.2 were elaborated. The phase formation was investigated by DTA/TG methods correlated with X-ray diffraction, performed on materials obtained in non-isothermal conditions. The diffraction data for the ceramics obtained by isothermal treatments emphasized the influence of the lanthanum on the crystal structure, inducing the doubling of the unit cell parameter. SEM investigations pointed out the lanthanum inhibitor effect on the grain growth process, leading to an uniform grain distribution.     

Etude sur le comportement thermique de quelques polymeres ignifugeants contenant du phosphore et des halogenes

The thermal behaviour a series of polyphosphonates was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The obtained data permitted the calculation of activation energies and reaction orders on decomposition zones by the Coats — Redfern method.     

Construction and analytical applications of a liquid-state iodide-selective electrode with a metal complex as exchanging site

Summary A new type of liquid-membrane iodide-selective electrode based on a 0.001M solution of tris(l,10-phenanthroline)ruthenium(II) iodide in 1,2-dichlorobenzene is described. The electrode has Nernstian behaviour down to 7×1O^–6M iodide. It has good selectivity towards halide (k _{I, Cl}=5.3×10^–6 andk _{I, Br}=1.6×10^–4) and other inorganic ions, and a linear response to iodide at pH-values from 3 to 9. It can be used either in direct iodide analyses or in potentiometric titrations. Titration of halide mixtures or of pseudohalides is also possible. The method has been used for determining the free formaldehyde present in dispersing agents.

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Herstellung und analytische Anwendung einer jodid-spezifischen Elektrode mit Flüssigmembran mit einem Metallkomplex als Austauscher

Zusammenfassung Eine neue jodid-spezifische Flüssig-Membran-Elektrode auf der Basis einer 0,001 M Lösung von Tris(1,10-phenanthrolin)-Ruthenium(II)-jodid in 1,2-Dichlorbenzol wurde beschrieben. Sie zeigt Nernstsches Verhalten bis zu 7×10^–8 M Jodid, gute Selektivität gegenüber Halogeniden (k _{I, Cl}=5,3× 10^–6 undk _{I, Br}=1,6×10^–4) und anderen anorganischen Ionen und ein lineares Verhalten gegenüber Jodid bei pH 3–9. Die Elektrode läßt sich für direkte Jodidbestimmungen oder für potentiometrische Titrationen verwenden. Die Titration von Halogenidgemischen oder Pseudohalogeniden ist ebenfalls möglich. Das Verfahren wurde zur Bestimmung von freiem Formaldehyd in Dispersionsmitteln verwendet.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Plutonium and americium in sediment samples along the Romanian sector of the Danube river and the Black Sea coast

The concentrations of²³⁸Pu,^239,240Pu and²⁴¹Am were determined in eight sediment samples, collected from the bed of the Romanian sector of the Danube river and the Black Sea coast during 1994 and 1995. Fusion with potassium carbonate was used to achieve complete dissolution of the samples. Tracers,²⁴²Pu and²⁴³Am, were added and the separation of plutonium from americium, uranium and thorium was performed by anion exchange. Americium was separated from uranium in two steps, using a conventional anion exchange resin and an extraction chromatographic resin for transuranics. After electrodeposition on stainless steel discs the nuclides were counted with -spectrometry with -PIPS detectors. The total plutonium concentrations obtained by this method were compared with the acid leachable plutonium concentrations reported for the same samples in a previous paper.     

Plutonium concentration distribution in bed load sediment samples along the Romanian sector of the Danube river and the Black Sea coast

The concentrations of²³⁸Pu and^{239, 240}Pu were determined in 12 sediment samples collected from the bed of the Romanian Danube river and Black Sea coast during June–September 1994. After the sample material has been properly prepared and²⁴²Pu tracer added, plutonium was separated from americium and curium by anion exchange. After electrodeposition on stainless steel discs the elements were counted with an -spectrometry system with silicon surface-barrier detectors. The^{239, 240}Pu concentrations range between 150 and 800 mBq kg^–1 dry, while the²³⁸Pu concentrations rise up to max 150 mBq kg^–1 dry. Although the chemical yields are rather low (51%) we appreciate the results as valuable since they report for the first time the distribution of the plutonium contamination along the Danube river and the Black Sea coast-Romanian sector.     

Analysis of Mepivacaine in Human Serum by Gas Chromatography After Solid-Phase Extraction

A method using solid-phase extraction (SPE) has been developed for analysis of mepivacaine in human serum. A procedure for isolation of mepivacaine and lidocaine (internal standard) from human serum by use of Chromosorb 104 (acrylonitrile–divinylbenzene polymer) as extraction adsorbent is described in detail. Analysis was performed by gas chromatography on an HP-INNOWax (cross-linked PEG) capillary column, with flame ionization detection, after splitless injection. Relative standard deviations ranged between 3.6 and 4.4 for a serum mepivacaine concentration of 0.5 g mL^–1 and between 4.7 and 5.9 for a concentration of 1 g mL^–1. Recoveries were approximately 95%. The method was applied in a stomatological clinic to healthy volunteers to whom anesthesia with mepivacaine was administered.