Palladium extraction from nitrate solutions by tertiary amines and quaternary ammonium salts

The mechanism of palladium extraction by trilaurylamine and trilaurylmethylammonium nitrate from nitric acid solutions was studied. The composition of the extracted compounds was determined by the Job method as well as by organic phase saturation. Both reagents were found to extract palladium as Am₂Pd/NO₃/₄ /Am=ammonium cation/.     

Theory-enforced Re-investigation of the Origin of the Large Metal–Carbon Bond Strength in PdCH2I+ and its reactions with unsaturated hydrocarbons

State-of-the-art ab initio studies demonstrate that the reaction Pd⁺ + CH₃I → PdCH₂I⁺ + H^. is endothermic by ca. 20 kcal/mol, which translates into a bond dissociation energy (BDE) of ca. 83 kcal/mol for the Pd⁺? CH₂I bond. This figure is in agreement with an experimental bracket of 68 kcal/mol < BDE(Pd⁺? CH₂I) < 92 kcal/mol. Based on these findings, the previously studied Pd⁺/CH₃I system was re-investigated, and double-resonance experiments demonstrate that the formation of PdCH₂I⁺ occurs stepwise via PdCH as a reactive intermediate. Further, ion/molecule reactions of PdCH₂I⁺ with unsaturated hydrocarbons are studied, which reveal the formation of carbon–carbon bonds in the gas phase.     

Comparison of the absolute calibration method with the method of standard addition for the determination of halothane in blood by gas chromatographic headspace analysis

As long-term exposure to exhaled halothane can be a cause of hepatitis and/or damage to the liver, the determination of halothane in blood is important in clinical practice. Gas chromatographic headspace analysis appears to be the most successful method. In the present study, two methods of quantitative evaluation of the analysis were compared by statistical treatment and direct comparison. The absolute calibration method was found to be unsuitable since it yields entirely unreliable results. This is due to different contents of lipoid and other components in the blood of the normal population, and this influences the vapour phase concentration of halothane and results in different values for the slopes of calibration curves for different blood samples. The standard addition method gives reliable results.     

pH-dependent electrochemical behaviour of hydrophilic ampholytic membranes

Ampholytic membranes were synthesized by copolymerizing (2-hydroxyethyl)methacrylate as the hydrophilic component, methacrylic acid and (N,N-diethylaminoethyl)methacrylate as ionogenic components (both ionogenic monomers in amounts 2.5 mol% or 10 mol%), and ethylenedimethacrylate as the crosslinking agent (3,5 or 10 mol%). The effects of pH on the swelling and membrane potentials of the membranes were investigated. The dependence of the membrane potentials on pH is characterized by the position of the isoelectric point and by the slope of the straight part of the dependence. This slope reflects the attained degree of ideality of the membrane. By varying the degree of cross linking and the content of ionogenic components, it is possible to vary the pH-dependent response of the membranes.     

Potential energy surface for the CCl4 + H --> CCl3 + ClH reaction: kinetics and dynamics study

An analytical potential energy surface for the gas-phase CCl4 + H --> CCl3 + ClH reaction was constructed with suitable functional forms to represent vibrational modes. This surface is completely symmetric with respect to the permutation of the four chlorine atoms and is calibrated with respect to experimental thermal rate constants available over the temperature range 297-904 K. On this surface, the thermal rate constants were calculated using variational transition-state theory with semiclassical transmission coefficients over a wider temperature range 300-2500 K, therefore obtaining kinetics information at higher temperatures than are experimentally available. This surface was also used to analyze dynamical features, such as tunneling and reaction-path curvature. In the first case, the influence of the tunneling factor is very small since a heavy chlorine atom has to pass through the barrier. In the second, it was found that vibrational excitation of the Cl-H stretching mode can be expected in the exit channel.     

Kb/Ka X-ray intensity ratios in calcium and potassium compounds

Summary Kb/Ka X-ray intensity ratios of some K and Ca compounds were studied. The samples were excited with 59.5 keV g-rays emitted from 75 mCi ²⁴¹Am radioisotope source and characteristic K X-ray from the samples were counted by means of an Si(Li) detector which has a resolution 155 eV at 5.9 keV. We found that Kb/Ka X-ray intensity ratios are changed by chemical effect for different K and Ca compounds. The experimental values were compared with the calculated theoretical values for elemental K and Ca.     

Solid-phase spectrophotometric microdetermination of iron with ascorbic acid and ferrozine

 A very sensitive and selective method for the determination of trace amounts of iron has been developed, based on the reduction of Fe(III) to Fe(II) by ascorbic acid, followed by chromogenic chelation of Fe(II) with ferrozine. The complex Fe(II)-ferrozine is easily sorbed on a dextran-type anion-exchange gel packed in a 1 mm cell, and the absorbance of the gel is measured directly at 569 and 800 nm. The extended linear range of the determination is 0.5–10 ng ml^-1 of iron (apparent molar absorptivity=4.4×10⁷ l mol^-1 cm^-1) and the precision (RSD) 1.3% for a concentration of 5 ng ml^-1 of iron (n=10). The detection limit for a sample volume of 1000 ml, using 0.040 g of anion-exchanger, corresponds to 0.12 ng ml^-1. The method has been successfully applied to the determination of iron in natural and waste waters, wine, soil extract and previously digested vegetal tissues, drugs and human hair. Received: 20 November 1995/Revised: 23 January 1996/Accepted: 26 January 1996     

Extraction of barium picrate into nitrobenzene in the presence of benzo-15-crown-5

From extraction experiments with ¹³³Ba as a tracer, the extraction constant corresponding to the equilibrium Ba²⁺(aq) + 2A^-(aq) + 2L(nb) BaL₂ ²⁺(nb) + 2A^-(nb) in the two-phase water-nitrobenzene system (A^- = picrate, L = benzo-15-crown-5; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (BaL₂ ²⁺, 2A^-) = 5.7. Furthermore, the stability constant of the benzo-15-crown-5 - barium complex in nitrobenzene saturated with water was calculated: log b_nb (BaL₂ ²⁺) = 14.6.     

Chromatographic analysis of phenethylamine-antihistamine combinations using C8, C18 or cyano columns and micellar sodium dodecyl sulfate-pentanol mixtures

The chromatographic behaviour of binary and ternary mixtures of several phenethylamines (phenylephrine, phenylpropanolamine, ephedrine, pseudoephedrine and methoxyphenamine) and antihistamines (pheniramine, carbinoxamine, doxylamine, chlorpheniramine, dexchlorpheniramine, dexbrompheniramine, diphenhydramine, tripolidine, azatadine and phenyltoloxamine), found in cough-cold pharmaceutical preparations, was studied using C8, C18 and cyano columns, micellar mobile phases of sodium dodecyl sulfate (SDS) and pentanol and UV detection. Using a C8 column and mobile phases of 0.05 mol l-1 SDS-6% v/v pentanol or 0.15 mol l-1 SDS-2% v/v pentanol at pH 7, more than 30 different phenethylamine-antihistamine combinations can be resolved in < 15 min. Intra- and inter-day repeatabilities and reproducibilities evaluated at three different drug concentrations (0.5, 5 and 25 micrograms ml-1, n = 10) were below 1.6, 2.5 and 2.4%, respectively. The drug amounts found in 18 formulations agreed with those declared by the manufacturers within the tolerance limits, and with those obtained using a mobile phase of 55% v/v methanol at pH 7. No interference was observed from other accompanying drugs such as acetylsalicylic acid, ascorbic acid, betamethasone, bromhexine, caffeine, codeine, dextromethorphan, paracetamol, prednisolone, salicylamide and tartrazine. The proposed procedure has the advantage over the conventional aqueous-organic procedure of using a small amount of organic solvent, which is highly retained in the SDS solution. The efficiencies are also greater. On the other hand, in the micellar system, the retentions of phenethylamines and antihistamines are similar, although the compounds can be easily resolved. In contrast, using the methanol-water mobile phase, the phenethylamines are weakly retained, whereas the antihistamines usually show a high retention.     

The infrared spectra of solid solutions of some iron and chromium oxides

Oxides Fe_2–x Cr _x O₃ (corundum-type) and Fe_3–y ,Cr _y O₄ (spinel-type) were studied by transmission IR spectroscopy. The wavenumbers corresponding to characteristic absorption maxima depend linearly on the composition of both types of solid solutions, i.e. onx andy. The results show that IR spectroscopy can contribute to the analysis of solid solutions of iron and chromium oxides and of the oxidation products of Fe-Cr alloys.The authors are indebted to Ing. P. Holba for the preparation of synthetic oxide samples. The cooperation of Yu. Borodkin and I. Zuika (Riga) who made the measurements in the far IR region is gratefully acknowledged.