Standardization of pH measurements based on the ion interaction approach

The Pitzer method was used to calculate the pH values on the conventional and “true” scales for the TRIS—TRIS·HCl−NaCl−H₂O buffer system in the 0–40 °C temperature region and 0–4 NaCl molality interval. This buffer can be used as a standard for pH measurements in a wide range of ionic strengths. The conventional scale is used in cells without a salt bridge. The “true” scale is recommended for pH measurements using cells with a salt bridge. At the same concentrations of the buffer solution, the “true” scale is essentially transformed into the scale of the National Bureau of Standards (NBS) of the USA. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 676–680, April, 2000.     

Phase equilibria in binary subsystems of urea–biuret–water system

Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the fusion enthalpy and temperature determination of the biuret (NH₂CO)₂NH (synthesis by-product of the urea fertilizer (NH₂)₂CO). Recommended values are Δ_m H = (26.1 ± 0.5) kJ mol⁻¹, T _m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested.     

Sol-Gel Microsphere Pelletisation Process for Fabrication of (U,Pu)O2, (U,Pu)C and (U,Pu)N Fuel Pellets for the Prototype Fast Breeder Reactor in India

A “dust-free” sol-gel microsphere pelletisation (SGMP) process has been developed for fabrication of (U,Pu)O₂, (U,Pu)C and (U,Pu)N fuel pellets containing around 15% plutonium for the forthcoming prototype fast breeder reactor (PFBR) in India. The objective was to produce homogeneous sintered pellets of ∼85% T.D. with a predominantly open-pore structure. Hydrated gel-microspheres of UO₃+PuO₂ and UO₃+PuO₂+C have been prepared from nitrate solutions of uranium and plutonium by the “ammonia internal gelation” process, using hexamethylene tetramine (HMTA) as an ammonia generator and silicone oil at 90±1°C as gelation bath. For oxide fuel pellets, the hydrated UO₃+PuO₂ gel-microspheres were calcined at around 700°C in Ar+8% H₂ atmosphere to produce “non-porous”, “free-flowing” and coarse (around 400 micron) microspheres which could be directly pelletised at 550 MPa to green pellets. The mixed oxide pellets were subjected either to low temperature (∼1100°C) oxidative sintering (LTS) in N₂+air containing ∼1500 ppm O₂ or to high temperature (1650°C) sintering, (HTS) in Ar+8% H₂. For monocarbide and mononitride pellets, hydrated gel-microspheres of UO₃+PuO₂+C were subjected to carbothermic synthesis in vacuum (∼1 Pa) and flowing nitrogen (flow rate: 1.2 m³/h) in the temperature range of 1450–1550°C respectively. The monocarbide and mononitride microspheres thus produced were relatively hard and required higher compaction pressure (∼1200 MPa) for making reen pellets which could be sintered to 85% T.D. in Ar+8% H₂ at 1700°C. The sintered oxide, monocarbide and mononitride pellets had a “blackberry” “open” pore microstructure with fine grain size. The microspheres retained their individual identity in the sintered pellets because during sintering densification took place mainly within and not between the microspheres.     

Redox-potentiometric/titrimetric analysis of aqueous iodine solutions

Redox-potential, titrimetric oxidation capacity and pH were used to analyze aqueous iodine solutions over a concentration range of five decades. By a single operation the equilibrium concentrations of I^–, I₂, I₃ ^–, I₅ ^–, I₆ ^2–, HOI and OI^– were assessed. Accuracy was most influenced by the redox-potential showing a repeatability of < ± 0.1 mV in solutions containing appreciable iodide (Lugol’s solution) which increased to ±1.5 mV at a 1:100 000 dilution. Together with the uncertainty of calibration this equals a calculated total error which ranges for “free iodine” ([I₂] + [HOI]), from ± 0.5% to ± 4.2% and for total iodide from ± 0.7 to ± 5.3%. Accuracy was assessed by a comparison of the evaluated equilibrium concentrations and parameters derived therefrom, such as total iodide and redox-potential, with measured resp. calculated values. The deviations at ionic strength < 0.1 M were below ± 3% and revealed a satisfactory accuracy of the method. As a unique feature it was possible to monitor the disproportionation in a iodide-free iodine solution with an initial concentration of 16% hypoiodic acid (HOI) at pH 7.6. Showing a half-life time of only ≈ 75 s it was confirmed that stability largely depends on HOI concentration. Received: 26 February 1998 / Accepted: 15 March 1998     

Selective water sorbents for multiple applications, 3. CaCl2 solution confined in micro- and mesoporous silica gels: Pore size effect on the “solidification-melting” diagram

In this communication we present a low-temperature “solidification-melting” phase diagram for CaCl₂/H₂O solutions confined in KSK and KSM silica gels. At salt concentrations of 0–48 wt. %, the diagram has been found to lie below the diagram reported for the bulk system by 15–30°C. It shows a depression of the solution melting point due to its confinment to the pores. Several other peculiarities of melting and solidification in this system are also reported and discussed. Beside fundamental interest, the data obtained could be of importance in many commercial areas such as refrigeration, accumulation of low temperature heat, frost prevention in building materials,etc.     

The spatial distribution of poly(methyloctylsiloxane) deposited by solvent evaporation in the pores of HPLC silica particles

Summary Poly(methyloctylsiloxane) (PMOS), sorbed into the pores of HPLC silica particles by solvent evaporation, can function as a useful stationary phase for reversed-phase chromatography. The present work addresses the question of how the PMOS is distributed in the pores. Measurements of the surface area (BET, N₂) of a series of partially loaded samples (0–40% PMOS, m/m) using a typical batch of HPLC silica (10 μm irregular particles with 6 nm pores) show that the specific surface area of the samples decreases linearly with the specific loading (mass of PMOS per gram of silica). This result is not consistent with a “film” model in which the PMOS is deposited uniformly on the pore walls, but is consistent with a model in which long segmented “plugs” of PMOS are deposited within the pore system. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Fourier transform-IR and 1H NMR studies on the structure of water solubilized by reverse aggregates of calcium bis(2-ethylhexyl) sulfosuccinate in organic solvents

The structure of water solubilized by reverse aggregates of calcium bis(2-ethylhexyl) sulfosuccinate in deuterobenzene and toluene has been probed by Fourier transform-IR and ¹H NMR spectroscopies. The ν_OD band of solubilized HOD (4% D₂O in H₂O) has been recorded as a function of the [water]/[surfactant] molar ratio, W/S. Curve fitting of this band showed the presence of a main peak at 2550 ± 13 cm⁻¹ and a small one at 2405 ± 15 cm⁻¹. As a function of increasing W/S, the frequency of the main peak decreases, its full width at half-height increases, and its area increases linearly. The ¹H NMR chemical shift of solubilized H₂O–D₂O mixtures at W/S = 18.1 has been measured as a function of the deuterium content of the aqueous nanodroplet. These data were used to calculate the so-called “fractionation factor” of the aggregate-solubilized water, the value of which was found to be unity. The results of both techniques show that reverse aggregate-solubilized water, although different from bulk water, does not seem to coexist in “layers” of different degrees of structure, as suggested, for example by the two-state water-solubilization model. Received: 12 July 1999/Accepted: 30 August 1999     

(NH4)2SiF6 evaporation in the presence of SiO2

The kinetics and mechanism of the solid-phase reaction between (NH₄)₂SiF₆ and silica at molar ratios of (0.5–5): 1 were studied. SiO₂ is bound with (NH₄)₂SiF₆ to form volatile NH₄SiOF₃, which abruptly enhances the ammonium hexafluorosilicate evaporation. The activation energy and rate constants of evaporation were calculated for an (NH₄)₂SiF₆ + SiO₂ (2: 1) mixture in the range 220–300°C. The reaction with crystalline SiO₂ has a higher yield than with an amorphous “white soot.” The role of the SiO₂ surface in the formation of the volatile products is discussed. The phase and chemical composition of the sublimates was studied.     

EPMA and Quantitative MCs+-SIMS of Metal-DLC Coating Materials

 Compositional characterization of metal-DLC (metal-containing diamond-like carbon) hard coatings is carried out by (WDS)-EPMA and MCs⁺-SIMS. EPMA enables accurate (± 5% relative) quantitative analysis including minor concentrations (0.1–10 at%) of N, O and Ar. Under conditions of “near-surface” EPMA (E₀ < 10 keV) the influence of surface oxide films on “pure” metal standards may be a limiting factor in respect of accuracy. Depth profiling of sufficiently “thick” layered structures (film thickness ≥ 2 μm) is carried out by EPMA-line scans along mechanically prepared bevels. The depth resolution is about 0.2 μm. SIMS in the MCs⁺-mode enables high resolution (< 20 nm) depth profiling of metal-DLC layered structures including the determination of H (1–20 at%). MCs⁺-SIMS, i.e. employing Cs⁺ primary ions and monitoring MCs⁺ molecular secondary ions (M is the element of interest) is presented as a promising route towards sufficiently accurate (10–20%) SIMS-quantification. Matrix-independent relative sensitivity factors for MCs⁺-SIMS are derived from homogeneous coating materials defined by EPMA. EPMA proves to be also useful to detect problems related to SIMS of Ar in metal-DLC materials. The combination EPMA-SIMS is demonstrated as an effective analytical strategy for quality control in industrial production and to support the development of metal DLC layered structures with optimum tribological properties.     

Packing of complex anions and effect of mutual ordering of heavy cations in structures with the paratungstate ion [H2W12O42]10−

The packing of [H ₂W₁₂O₄₂]¹⁰⁻ polyanions in seven known crystal structures is analyzed. The centers of the polyanions are arranged according to the law of the F- cell (3 cases) or I- cell (2 cases) or according to a more complex law. “Coherence” in the arrangement of heavy W atoms belonging to different polyanions is established: there are crystallographic planes with high concentrations of these atoms;this is an effect of superstructural ordering up to formation of the cation sublattice with light “filler” atoms (K, Mg, Na, N) partly addressed to the sites of the sublattice. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 4, pp. 732–738, July–August, 1997.     

Self-organization of sulfopolystyrene ionomers in solutions: Dependence on the polarity of the solution and the content of ionogenic groups in chains

The self-organization of ionomers of sulfonated polystyrene containing different amounts of SO₃Na ionogenic groups (0.5, 1.35, and 2.6 mol %) in three solvents (benzene, toluene, and THF) is studied via the methods of neutron scattering. It is shown that, in toluene, ionogenic groups form “effective” chains of up to 10–20 macromolecules owing to aggregation. In benzene, chains of both the PS precursor and ionomers are surrounded by volume solvate shells in the form of ∼4-nm-dia tubes that hamper interaction between ionomers via ionogenic groups. The tendency of ionomer chains toward aggregation in benzene is enhanced as the content of polar groups in chains is increased to 2.6 mol %. The diameter of solvate shells around chains decreases to ∼1 nm, and chains associate to form denser structures. In this case, the degree of integration of macromolecules turns out to be smaller than that in toluene. In THF, the processes of solvation and structuring of PS precursor chains are well defined and compete with tendencies toward association through ionogenic groups in solutions of ionomers. The formation of developed supramolecular structures in THF is hindered by the shielding of the potentials of interaction between ion pairs because of a high dielectric constant of the solvent.     

Characterization of a sealed Americium–Beryllium (AmBe) source by inductively coupled plasma mass spectrometry

Two Americium–Beryllium neutron sources were dismantled, sampled (sub-sampled) and analyzed via inductively coupled plasma mass spectrometry (ICP-MS). Characteristics such as “age” since purification, actinide content, trace metal content and inter and intra source composition were determined. The “age” since purification of the two sources was determined to be 25.0 and 25.4 years, respectively. The systematic uncertainties in the “age” determination were ±4% 2σ. The amount and isotopic composition of U and Pu varied substantially between the sub-samples of Source 2 (n = 8). This may be due to the physical means of sub-sampling or the way the source was manufactured. Source 1 was much more consistent in terms of content and isotopic composition (n = 3 sub-samples). The Be–Am ratio varied greatly between the two sources. Source 1 had an Am–Be ratio of 6.3 ± 52% (1σ). Source 2 had an Am–Be ratio of 9.81 ± 3.5% (1σ). In addition, the trace element content between the samples varied greatly. Significant differences were determined between Sources 1 and 2 for Sc, Sr, Y, Zr, Mo, Ba and W.     

2D LC Separation and Determination of Bradykinin in Rat Muscle Tissue Dialysate with On-Line SPE-HILIC-SPE-RP-MS

A 2D liquid chromatography (LC) system using hydrophilic interaction chromatography (HILIC) and reversed phase columns has been employed for comprehensive (LC × LC) separation of rat muscle tissue micro-dialysate. Incorporation of an on-line reverse-phase solid phase extraction (SPE) enrichment column in front of the first dimension enabled aqueous samples with high salt concentrations to be injected directly without compromising the chromatographic performance of the HILIC column. Since the SPE enrichment column allowed injection of large sample volumes (e.g. 450 μL), a capillary HILIC column (inner diameter 0.3 mm) could be employed instead of a larger column which is often used in the first dimension to load sufficient amounts of sample. The two chromatographic dimensions were connected using a column selector system with 18, 1.0 mm I.D. C₁₈ “transition” SPE columns. A PLRP C₁₈ column was used in the second dimension. The 2D LC system’s performance was evaluated with a tryptic digest mixture of three model proteins. Good trapping accuracy (HILIC→transition SPE→RP recovery >95%) and repeatability (within-and between day retention time RSDs of first and second dimension chromatography >1%) was achieved. A dialysis sample of rat muscle tissue was separated with the 2D system, revealing complexity and large differences in concentrations of the various compounds present, factors which could potentially interfere with the quantification and monitoring of two target analytes, arg-bradykinin and bradykinin. Subsequently, “Heart-cut” 2D LC-electrospray–mass spectrometry (ESI–MS) with post-column on-line standard injection was employed to monitor arg-bradykinin and bradykinin levels as a function of various muscle conditions. The method’s quantification precision was RSD = 3.4% for bradykinin.     

The kinetics and main pathways for the liquid-phase oxidation of cyclohexene by air in the presence of cobalt,chromium, iron,and nickel µ<Subscript>3</Subscript>-oxotrimetallohexapivalates

It was found that during the liquid-phase oxidation of cyclohexene (CH) by air (323–343 K) in the presence of a series of homo-and heteronuclear μ ₃-oxotrimetallohexapivalates with a M₂M′O (M, M′ = Co, Cr, Fe, Ni) core insignificant amounts of the corresponding epoxide are formed, and 3-hydroperoxy-2-cyclohexene (HP), 3-hydroxy-2-cyclohexene (CHol), and 2-cyclohexen-3-one (CHone) accumulate in the oxidate. It is suggested that CHone and CHol are “dead-end” products from the oxidation of CH under the investigated conditions while the HP is a unique “intermediate-damper” that gives rise to the realization of alternative paths (catalytic cycles) for the formation of these products. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 85–90, March–April, 2007.     

Speciation of rare earth elements in soil by sequential extraction then HPLC coupled with visible and ICP-MS detection

The distribution of rare earth elements (REE) in a pooled soil sample collected from Zhangzhou, Fujian Province, China, was screened by a five-step sequential extraction procedure coupled with ICP–MS determination after preconcentration of REE and removal of the matrix by extraction with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP). The results showed that the distribution of REE in the different fractions of the pooled soil sample studied followed the order soluble species (46.76%) > species bound to organic matter (22.08%) > species in the residue (16.77%) > species bound to Fe–Mn oxides (2.02%). An effective method for speciation of REE, which utilized weak cation-exchange HPLC separation hyphenated with post-column derivatization and visible or on line ICP–MS detection, was, moreover, developed and successfully applied to the speciation of REE in the soluble extract of the pooled soil sample. The stability of known complexes of lanthanum during the HPLC separation was investigated with fluoride, citrate, and ethylenediamine tetraacetic acid (EDTA) chosen as ligands modeling those in the soil. REE in the soluble extract of the pooled soil sample were subsequently classified into three types of species –≤ + 1 charged complexes (negatively charged, neutral, and +1 charged), + 2 charged complexes, and “free” REE species. This method is expected to be useful for identification of bioavailable (or toxic) species of REE in environmental samples. Received: 14 November 2000 / Revised: 26 January 2001 / Accepted: 30 January 2001     

Orientation of water molecules by the diamond surface

The properties of water in suspensions of diamond powders with particle sizes from 125–160 μm to 2–10 nm were studied. The dielectric constant of water in these suspensions changed from 1.3 × 10³ to 2.6 × 10⁶. The particle sizes correlated with the dielectric constants. The sound velocity of “diamond” water exceeded the initial velocity by 15–20 m/s. The crystals isolated from “diamond” water after prolonged storage had specific diffraction patterns and IR spectra. Their composition was not determined.     

Evaluation of high-performance liquid chromatography for determination of phenolic compounds in pear horticultural cultivars

Summary An analytical evaluation of an HPLC method with diode array detection to separate and quantify polyphenolic compounds from pears has been made. The method was applied to the quantitative analysis of phenolics from five pear horticultural cultivars (“Agua”, “Blanquilla”, “Conference”, “Pasagrana” and “Decana”) in both peel and pulp matrices and evaluated for precision and accuracy. Precision was taken as the reproducibility in peak area of the polyphenols of interest as well as in the slope of calibration graphs. Values ranged 2–5%. Accuracy was evaluated by recovery of all polyphenolic compounds from both peel and pulp in all pears investigated. Accuracy values ranged 92–102%, and were independent of the polyphenolic structure, horticultural cultivar and matrix. Identification was by comparing retention times and UV spectra with those of standards when commercially available. When not available commercially, provisional identification was according to spectral characteristics as well as from isolation and hydrolysis data. Application of the method revealed differences between peel and pulp in all cases studied; the higher levels of phenolics were found in the peels. “Decana” and “Pasagrana” cultivars showed the highest phenolic content compounds whereas “Conference” showed the lowest.     

Adsorption and electrophysical properties of semiconductors of the InSb-CdS system

Adsorption and the electrophysical properties (changes in electrical conductivity) of thin film solid solutions and binary components of the new InSb-CdS system are studied by means of piezoquartz microweighing, IR spectroscopy and probe compensation in the temperature range of 273–353 K and a range of adsorbate gas (NH₃, NO₂) pressures of 0.2–9.8 Pa. The areas of physical and chemical adsorption accompanied by the charging of the (mostly positive) surface are determined. The mechanisms and regularities of adsorption as a function of external conditions and composition of the system are established, and certain similarities and patterns of changes in the adsorption and electroconductivity, and parallelisms of the “acidbase characteristic-composition,” “adsorption characteristic-composition,” and “electrophysical characteristics-composition” dependences are described. These prove to be useful in studying the adsorption mechanism and in identifying the most active components of the system relative to NH₃ and NO₂, proposed as materials for respective sensors/detectors.     

Physicochemical characterization of nicergoline and cabergoline in its amorphous state

Formulation of poorly water-soluble crystalline drugs into their more soluble amorphous form is a common approach for improving their bioavailability. In this study, the amorphous forms of nicergoline (NIC) and cabergoline (CAB) were obtained by different methods (melting and precipitation under solvent evaporation). The physicochemical characteristics of the samples were determined by HPLC, differential scanning calorimetry (DSC), thermogravimetry, and X-ray powder diffractometry. The physical stability of the amorphous forms was investigated by DSC by considering how the onset temperature and the enthalpy content at the glass transition vary with aging time and temperature. Using the Kohlrausch–Williams–Watts equation on the data obtained from the experiments, the “mean molecular relaxation time constant” (τ) was estimated. This parameter was used to understand the stability of NIC and CAB in their glassy state at different temperatures, and results showed that their stability is adequate to enable the formulation of these drugs into solid dosage forms.     

Treatment of water-induced curvature of the DSC heat flow rate signal

In samples containing a volatile phase, quite often the evaporation of the volatile substance during heating causes appreciable curvature of the DSC heat flow rate signal as function of temperature, making it difficult to quantify thermal transitions and reorganization phenomena occurring in the same temperature range. This is the case for e.g. polyamide–water, polyamide–alcohol, and polypropylene–water systems, thus complicating the study of polymer crystallization, melting, and metastability by DSC. In this study, maleic anhydride-grafted polypropylene particles of sub-micrometer diameters dispersed in water are discussed. These samples show, upon cooling from the melt, different degrees of extra supercooling in crystallization and several phenomena in the subsequent heating, like reorganization of a crystalline phase into another one, perfecting of crystallites, and melting. All these phenomena are difficult to analyze quantitatively due to the mentioned curvature of the DSC trace. In this article two methods, the “Reference” and “Extrapolation from the melt” methods, are described to correct for the influence of evaporation on the DSC heat flow rate signal and for the baseline signal, enabling the discussion of the transitions by way of the excess heat flow rate as function of temperature.