Insight into the extractability of metals from soils using an implementation of the linear adsorption isotherm model

This paper deals with an often overlooked artifact in sequential and single extraction of metals from soils, viz. the volume to mass (V/m) ratio as a potential source for inadequate extraction yields. We offer a theoretical framework to get a grip on this intricate parameter and came up with a model based on a linear adsorption isotherm to derive the correct maximal metal extractability for a certain extractant. We verified the model experimentally using 0.1 mol l⁻¹ nitric acid for extraction of seven metals (Cr, Co, Cu, Cd, Pb, Ni and Zn) from an urban soil sample, and concluded that commonly used V/m ratios in the range of 10-40 ml g⁻¹ may give as much as 50% too low extraction yields. Thus, a strong caveat is in place as to be very critical what V/m ratios to use and preferably apply the model derived to obtain the correct maximal extractability using a variable V/m ratio method.     

Osmotic Coefficients of Aqueous Solutions of Some Poly(oxyethylene) Glycols at the Freezing Point of Solution

Summary. The freezing temperatures of dilute aqueous solutions of some poly(oxyethylene) glycols (PEG, HO–(CH₂CH₂O) _n –H, n varying from 4 to 117) were measured over a solute to solvent mass ratio from 0.0100 to 0.3900. The second and third osmotic virial coefficient (A ₂₂ and A ₂₂₂) of poly(oxyethylene) glycols in aqueous solution were determined. The molecular weight dependence of the second virial coefficient can be described by a simple relation A ₂₂=2×10^–5 M _n ^1.86, and the third virial coefficient is A ₂₂₂=0.038A ₂₂ ². The activity coefficients of the solute were calculated using the Gibbs-Duhem equation as applied by Bjerrum. From the osmotic and activity coefficients the excess Gibbs energies of solution, as well as the respective partial molar functions of solute and solvent and the virial pair interaction coefficients for the excess Gibbs energies were estimated. The second and the third osmotic virial coefficients are correlated with the Mc-Millan-Mayer virial coefficients.     

Simultaneous radiochemical neutron activation analysis of iodine, uranium and mercury in biological and environmental samples

The determination of medium and long-lived nuclides can be combined with short-lived ones if a medium or long irradiation is made prior to the short irradiation and radiochemical processing. Thus, an RNAA method previously developed for determination of iodine based on the reaction¹²⁷I(n,)¹²⁸I (T _1/2=25 m) using oxygen flask ignition of the irradiated sample, followed by solvent extraction with an iodine-iodide redox cycle, was combined with an overnight preirradiation to induce the²³⁵U fission product¹³³I (T _1/2=20.8 h). By reactivating the sample, cooled 1–2 days after the first irradiation, for few minutes both¹²⁸I and¹³³I could be quantified in the separated iodine fraction. Non-combustible inorganic materials (e.g., sediment, soil, etc.) can be successfully ignited after mixing with excess cellulose powder. Chemical yields for iodine were determined spectrophotometrically in the organic phase, while homogeneously spiked Whatman cellulose powder was used as uranium standard. Mercury is also released on ignition and collected in the absorbing solution, from where it was separated by toluene extraction. Its chemical yield was determined for each aliquot using²⁰³Hg tracer and counting on an LEPD. Results for some suitable SRMs are presented, and the general features of the double irradiation technique discussed.     

Heats of Mixing of Mixed Solvent Solutions of Alkali Metal Salts of Substituted Benzenesulfonic Acids

The enthalpy change on mixing solutions of methyl-substituted benzenesulfonic acids and their salts, with salts having a common cation or anion, at constant ionic strength in mixtures of 1,4-dioxane with water, were measured at 25°C. The heat effects of mixing solutions having a common anion increase almost linearly with the reciprocal value of the dielectric constant of the solvent. The heat effects of mixing solutions having a common cation, which are all negative in water-rich solutions, become endothermic after a certain value of the dielectric constant is passed. The results are discussed in terms of the solute-solvent structural properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Exploring the local conformational space of a membrane protein by site-directed spin labeling

Molecular modeling based on a hybrid evolutionary optimization and an information condensation algorithm, called GHOST, of spin label ESR spectra was applied to study the structure and dynamics of membrane proteins. The new method is capable of providing detailed molecular information about the conformational space of the spin-labeled segment of the protein in a membrane system. The method is applied to spin-labeled bacteriophage M13 major coat protein, which is used as a model membrane protein. Single cysteine mutants of the coat protein were labeled with nitroxide spin labels and incorporated in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers. The new computational method allows us to monitor distributions of local spatial constraints and molecular mobility, in addition to information about the location of the protein in a membrane. Furthermore, the results suggest that different local conformations may coexist in the membrane protein. The knowledge of different local conformations may help us to better understand the function-structure relationship of membrane proteins.     

The Dold-Lashof-Fuchs construction revisited

Sia dato uno spazio topologicoE con azione di un monoide topologicoH e siaE→B una funzione continue che, su ogni apertoU di una partizione dell'unità diB, sia, a meno di omotopia, la proiezioneU×H→U (ovvero una fibrazione numerabile). Un classico risultato di A. Dold e R. Lashof (1959) permette di costruire, a partire daE→B, una funzione continuaE _∞→B_∞, conE _∞ debolmente contraibile e munito di azione diH: laH-fibrazione universale associata daH. Tale funzione, in generale, non è purtroppo numerabile e quindi non si presta alla classificazione delleH-fibrazioni numerabili. Successivamente (1971), M. Fuchs ha trovato un modo di modificare la costruzione di Dold-Lashof per recuperare la numerabilità. La costruzione di Dold-Lashof-Fuchs è, da allora, uno dei principali strumenti nella teoria degli spazi classificanti di monoidi topologici, anche se vi è un uso di topologie alquanto complesse e quindi poco maneggevoli. In questo lavoro ci proponiamo di mostrare come, lavorando nella categoria conveniente deik-spazi, sia possibile descrivere la costruzione di Dold-Lashof-Fuchs in modo estremamente semplificato ed adattarla anche alla classificazione delleF-fibrazioni numerabili.

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Conferenza tenuta da R. Piccinini il 15 maggio 1995     

Memory effect of pH glass electrodes in emulsions

In the pH measurements of very viscous w/o emulsions, having a high electrical resistance, the "memory effect" of glass membrane is observed. Its dependencies on type of glass and on pretreatment conditions of electrode membrane, and its relation to the gel layer properties are presented. The results complement the findings of other authors.     

Ion chromatographic determination of alkali and alkaline earth metals in mineral waters

Summary The rapid, simultaneous, suppressed ion chromatographic determination of alkali, alkaline earth metals and ammonium in highly mineralized waters has been examined using the novel cation exchange IonPac CS12 column. General ability for the determination of lithium, sodium, ammounium, potassium, magnesium, calcium and strontium in concentrations from a few g to several mg per liter was studied. The relative standard deviations of retention times of all seven cations were below 0.7% and the relative standard deviations of the measurements of peak areas and peak heights were mostly below 5%. Six natural mineral waters of different types were selected for evaluation of the method. It was not possible to determine lithium in the one run and ammonium usually partially coelutes with sodium precluding quantitative determination. Strontium was undetectable because of the necessary dilutions. All the reltionships between peak areas and concentrations or peak height and concentrations were linear and there was also no evidence of the effect of different matrices on the slope of regression lines.     

Tensor products over abelian Walgebras

Tensor products of Calgebras over an abelian Walgebra are studied. The minimal Cnorm on is shown to be just the quotient of the minimal Cnorm on if or is exact.

     

The stability of the exponential equation

We generalize the well-known Baker's superstability result for exponential mappings with values in the field of complex numbers to the case of an arbitrary commutative complex semisimple Banach algebra. It was shown by Ger that the superstability phenomenon disappears if we formulate the stability question for exponential complex-valued functions in a more natural way. We improve his result by showing that the maximal possible distance of an -approximately exponential function to the set of all exponential functions tends to zero as tends to zero. In order to get this result we have to prove a stability theorem for real-valued functions additive modulo the set of all integers .