Oxidation process of MoOxCy to MoO3: kinetics and mechanism

A non-isothermal kinetic study of the oxidation of “carbon-modified MoO₃” in the temperature range of 150-550°C by simultaneous TGA-DTA was investigated. During the oxidation process, two thermal events were detected, which are associated with the oxidation of carbon in MoO_xC_y and MoO₂ to MoO₃. The model-free and model-fitting kinetic approaches have been applied to TGA experimental data. The solid state-kinetics of the oxidation of MoO_xC_y to MoO₃ is governed by F1 (unimolecular decay), which suggests that the reaction is of the first order with respect to oxygen concentration. The constant (Ea)_α value (about 115±5 kJ/mol) for this first stage can be related to the nature of the reaction site in the MoO₃ matrix. This indicates that oxidation occurs in well-defined lattice position sites (energetically equivalent). On the other hand, for the second stage of oxidation, MoO₂ to MoO₃, the isoconversional analysis shows a complex (Ea)_α dependence on (α) and reveals a typical behavior for competitive reaction. A D2 (two-dimensional diffusion) mechanism with a variable activation energy value in the range 110-200 kJ/mol was obtained. This can be interpreted as an inter-layer oxygen diffusion in the solid bulk, which does not exclude other simultaneous mechanism reactions.     

Cis- and trans-3-hexene: infrared spectrum in liquid argon solution, ab initio calculations of equilibrium geometry, normal coordinate analysis, and vibrational assignments

The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C₂ and C_s) of cis-3-hexene and of the three lowest energy rotamers (symmetry C_i, C₂, and C₁) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the ΔH of conversion between the rotamers C₂ and C_s of cis-3-hexene and between the rotamers C_i, C₂, and C₁ of trans-3-hexene.     

Gas permeation of porous organic/inorganic hybrid membranes

Selective gas permeation of porous organic/inorganic hybrid membranes via sol-gel route and its thermal stability are described. Separation performance of the hybrid membrane was improved compared with porous membranes governed by the Knudsen flow, and gas permeability was still much higher than that through nonporous membranes. Additionally, it was shown that these membranes were applicable at higher temperatures than organic membranes.SEM observation demonstrated that the thin membrane was crack-free. Nitrogen physisorption isotherms showed the pore size was in the range of nanometers. Gas permeability through this membrane including phenyl group was in the range of 10^–8 [cc(STP) cm/(cm² s cmHg)] at 25°C. The ratios of O₂/N₂ and CO₂/N₂ were 1.5 and 6.0, respectively, showing the permeation was not governed by the Knudsen flow. The permeability decreased as the temperature increased. Furthermore, the specific affinity between gas molecules and surface was observed not only in the permeation data of the hybrid membranes but in the physisorption data. These results suggested that the gas permeation through the hybrid membrane was governed by the surface flow mechanism.Thermal analysis indicated that these functional groups were still stable at higher temperatures. The phenyl group especially remained undamaged even at 400°C.     

Solid phase extraction and analysis of horse urine for aminocaproic acid

Summary A rapid and efficient procedure is described for extraction and determination of aminocaproic acid in horse urine. Urine was extracted by passing through a bonded silica column (Bond-Elut). The adsorbed drug was washed free of endogenous materials before being eluted. The extract was then examined by thin-layer chromatography and HPLC. The purity of the extract was determined by gas chromatography-mass spectrometry.     

Determination of organosilicon compounds in water by atomic absorption spectroscopy

Summary An extraction technique is described for the determination of ppm concentrations of both hydrophobic and hydrophilic methylsiloxane compounds in water, based on a single extraction with a mixed solvent of (11) l-pentanol and methyl isobutyl ketone followed by the determination of the silicone compounds extracted into the mixed solvent by atomic absorption spectroscopy. The method is applicable over the concentration range 0.3–30 ppm Si. Standard deviation in the case of 10 ppm Si is 0.313.

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Bestimmung von siliciumorganischen Verbindungen in Wasser mit Hilfe der Atomabsorptions-Spektralphotometrie

Zusammenfassung Zur Bestimmung von ppm-Konzentrationen an hydrophoben und hydrophilen Methylsiloxanverbindungen im Wasser wird ein Extraktionsverfahren beschrieben. Hierbei wird nach einfacher Extraktion mit l-Pentanol/Methylisobutylketon (11) das Silicium im Extrakt mit Hilfe der AAS bestimmt. Der erfaßbare Konzentrationsbereich liegt bei 0,3–30 ppm Si. Die Standardabweichung beträgt bei 10 ppm Si 0,313.

     

Untersuchungen zur mikroanalytischen Bestimmung der langkettigen Fetts?uren im Blut

Zusammenfassung Für die im Plasma an Albumin gebundenen sog. freien Fettsäuren (FFS) wird ein neues gas-chromatographisches Analysenverfahren vorgestellt. Das Probenvolumen beträgt 50 l Serum oder Plasma. Die Extraktion erfolgt in 1,1 ml CHCl₃/CH₃OH (21, v/v) mit n-Heptadecansäure als innerem Standard (0,05 Val C₁₇₀/ml). Nach Eindampfen am Rotationsverdampfer werden die FFS im verschlossenen Reaktionskölbchen mit 20 l CH₃J/Essigsäureäthylester (11, v/v) über festem K₂CO₃ bei 90°C 1 h verestert. Die Varianz des Verfahrens errechnet sich bei 15 Parallelbestimmungen zu 4,85%.Vortrag anläßlich der Tagung Spurenanalyse, 2. bis 5. April 1973 in Erlangen.     

Net information measures for modified Yukawa and Hulthén potentials

The dimensional analyses of the position and momentum variances‐based quantum mechanical Heisenberg uncertainty measure, as well as the entropic information measures given by the Shannon information entropy sum and the product of Fisher information measures are carried out for two widely used nonrelativistic isotropic exponential‐cosine screened Coulomb potentials generated by multiplying the superpositions of (i) Yukawa‐like, ?Z(e^?μr/r), and (ii) Hulthén‐like, ?Zμ(1/(e^μr ? 1)), potentials by cos(bμr) followed by addition of the term a/r², where a and b ≥ 0, μ are the screening parameters and Z, in case of atoms, denotes the nuclear charge. Under the spherical symmetry, all the information measures considered are shown to be independent of the scaling of the set [μ, Z] at a fixed value of μ/Z, a, and b and the other parameters defining the superpositions of the potentials. Numerical results are presented, which support the validity of the scaling properties. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Quantitative HPTLC determination of prostaglandin E1

Direct in situ determination of PGE₁ in dioxane/water (1:1) at concentrations between 50 μg/ml and 1 mg/ml is described. HPTLC of PGE₁ was carried out on HPTLC Kieselgel 60 o.F. plates; application (200 nl) was with a Nano-Appllcator and ethyl acetate/formic acid (400:5, v/v) served as mobile phase. The spots were located by dipping the plates into a 3% cupric acetate solution in 15% aqueous phosphoric acid, followed by heating at 120°C for 15 min. The plates were then evaluated directly at λ = 345 nm by chromatogram spectrometry. The coefficient of variation is 3.6%.     

Sampling procedure and a radio-indicator study of mercury determination in whole blood by using an AMA 254 atomic absorption spectrometer

A sampling procedure appropriate for the determination of mercury in whole blood was tested by using both inactive controls and a ¹⁹⁷Hg mercury radio-indicator. To exclude the influence of the instrumental device (an AMA 254 single-purpose mercury atomic absorption spectrometer) on the determination of mercury in whole blood, the function of the instrument was checked by using rat blood with metabolised ¹⁹⁷Hg. The measurement procedure was found to be free of errors. However, the study showed that the material used for the sampling vessels is a crucial parameter for obtaining accurate analytical results. The stability of solutions and samples was tested towards polyethylene (PE) and polypropylene (PP) vessels. PE displayed a time-dependent increase in the mercury content both in the samples and in the blood control material. The probable cause of this increase was direct contamination from the material of the vessel and/or diffusion of mercury from the environment through the vessel walls related to a strong complexing affinity of the sample matrix. This assumption was confirmed by supplying the vessels with the complexing agent Na₂EDTA (0.05 mol L^–1). Commercial PP vessels for blood sampling (Sarstedt S-Monovette Metall Analytik) did not give rise to statistically significant variations in mercury content in the samples and blood control material over a 30-day period.     

Effects of citrate on the composition and enzymic coagulation of colloidal bovine casein aggregates

Colloidal casein aggregates (CCA) prepared from soluble whole bovine caseinates in the presence of Ca²⁺ and phosphate (Pi) ions by addition of different citrate (Cit) concentrations showed different mineral and proteic composition. Citrate concentration conditions the Ca and Pi concentrations incorporated into CCA, probably due to the complexing effect of this anion on calcium. A significant change in the incorporated Ca/Pi ratio at 8 mM citrate could very likely be associated to changes in CCA net charge. The incorporation of individual caseins to the colloidal particles obtained, as well as their average size and size distribution, depended also on the Cit concentration used [Cit]_P. α_S- and β-caseins assembled in the CCA structure sharply decreased at a [Cit]_P higher than 15 mM, i.e., at a low Ca²⁺ concentration in the aggregates, showing that the presence of this cation is necessary for the incorporation of these caseins. An inverse relationship between the aggregation step rate in CCA enzymic coagulation and their average size was observed. The aggregation rate vs the average size curve obtained at [Cit]_P 8 mM clearly differed from the curves obtained at 10 and 12 mM, respectively, a fact probably related to a change in the CCA net charge. This behavior showed the effect of citrate concentration on CCA functional properties.