Preparation and structure of poly(4,4′-oxydiphenylene)pyromellitimide asymmetric ultrafiltration membranes

A process was developed for preparing asymmetric ultrafiltration poly(4,4′-oxydiphenylene)pyromel litimide membranes, involving wet forming of the membranes from the prepolymer, followed by catalytic solidphase thermal transformation of the prepolymer into the polyimide. The influence exerted on the structure and characteristics of the membranes by the compositions of the forming solution and precipitation bath, and also by thermal imidization conditions was examined. The optimal conditions were determined for preparing asymmetric ultrafiltration poly(4,4′-oxydiphenylene)pyromellitimide membranes exhibiting the water permeability coefficient of (10−500) × 10⁻⁶ m³ m⁻² s⁻¹ atm⁻¹ and molecular weight cut-off in the range (5−100) × 10³ g mol⁻¹.     

Voltammetric determination of 2,4-dinitrophenol and 2,5-dinitrophenol using a poly-aspartic acid modified electrode1

In pH 5.0, 0.1 mol l⁻¹ NaAc-HAc buffer solution, 2,4-dinitrophenol and 2,5-dinitrophenol exhibited sensitive and distinguishable voltammetric responses at the glassy carbon electrode modified with poly-aspartic acid. By measuring the reduction peak currents of nitro groups in different positions, dinitrophenol isomers have been determined simultaneously and quantitatively. The linear calibration ranges were 1.1 × 10⁻⁶–6.0 × 10⁻⁴ mol l⁻¹ for 2,4-dinitrophenol and 7.0 × 10⁻⁷–6.0 × 10⁻⁴ mol l⁻¹ for 2,5-dinitrophenol, with detection limits of 2.7 × 10⁻⁷ and 1.1 × 10⁻⁷ mol l-1 respectively. This method has been applied to the detection of dinitrophenols in simulation water sample, and the recovery was from 96.7 to 102.5%.     

Equilibrium constants for the formation of Cu(I) halide complexes

The stoichiometric equilibrium constants, K ₃ ^* , for the formation of CuX ₃ ²⁻ from CuX ₂ ⁻ +X⁻ where X=Cl and Br, have been determined from spectral measurements. The measurements were made in NaCl and NaBr solutions from I=0.5 to 6.0m at 5, 25 and 45°C. The measured constants were extrapolated to infinite dilution using the Pitzer equations. The Pitzer parameters, β⁰, β¹ and C^φ, for the interaction of Na⁺ with CuX ₂ ⁻ and CuX ₃ ²⁻ are briefly discussed.     

Anti- and pro-oxidant properties of sodium 2-mercaptoethane sulphonate (Mesna)

The ^•OH and the NO₂ ^• radicals generated pulse radiolytically in N₂O-saturated aqueous solution at pH 8–8.5 oxidize Mesna to form the corresponding thiyl radicals which on reaction with thiolate ions form an RSSR^{• −} type of transient with λ_max = 420 nm. The rate constants for the formation of these transients were determined. In the absence of O₂ at pH=6, the RS^• radicals formed show an absorption maximum at 360 nm and an ε=200±50 dm³ mol⁻¹ cm⁻¹. The rate constant k (^•OH+RSH) was 6×10⁹ dm³ mol⁻¹ s⁻¹ as determined from competition kinetics. In the presence of O₂ the Mesna thiyl radical was seen to rapidly add oxygen to form an RSOO^• type of species with λ_max = 535 nm, ε=700±50 dm³ mol⁻¹ cm⁻¹ and k (RS^•+O₂)=1.3×10⁸ dm³ mol⁻¹ s⁻¹. Both the RS^• and the RSOO^• radicals formed by the oxidation of Mesna were able to abstract H-atoms from ascorbate ions and k(RS^• +AH⁻)=~k(RSOO^•+AH⁻)=~6−7×10⁸ dm³ mol⁻¹ s^−1-. Moderately strong oxidants like CCl₃OO^• and the (CH₃)₃CO^• radicals, having a reduction potential of +1.4−1.6 V vs NHE were unable to oxidize Mesna. The results thus reflect on the pro- and anti-oxidant properties of Mesna.     

A novel electrochemical method for the determination of trinitrophenol

In pH 5.5, 0.1 mol l⁻¹ HAc-NaAc buffer solution, trinitrophenol has been determined quantitatively with differential pulse voltammetry by detecting its reduction peak currents at the glassy carbon electrode. The detection sensitivity was enhanced significantly by the addition of the surfactant of cetyl pyridinium chloride, and the enhancement mechanism was also studied in detail. The linear calibration range was 8.0 × 10⁻⁷ to 2.0 × 10⁻⁴ mol l⁻¹, and the detection limit was established to be 1.9 × 10⁻⁷ mol l⁻¹. This method has been applied to the determination of trinitrophenol in water sample, and the recovery was from 97.6 to 103.5%.     

Contents of238Pu,239,240Pu and137Cs in sediments and shore depositions of the Vltava river in 1995–1996

The²³⁸Pu,^239,240Pu and¹³⁷Cs concentrations in sediments and shore deposition samples of the Vltava river were determined.^239,240Pu and¹³⁷Cs concentrations in sediment samples (five locations) ranged from 19.6 to 124.8 mBq·kg⁻¹ and from 1.8 to 28.2 Bq·kg⁻¹, respectively. The²³⁸Pu,^239,240Pu and¹³⁷Cs concentrations in shore deposition samples (four locations) ranged from 2 to 16.8, from 26.8 to 477.2 mBq·kg⁻¹, and from 1.6 to 86.3 Bq·kg⁻¹, respectively. The superficial activity of studied radionuclides in shore deposition areas was determined and radionuclide origin at studied locations was discussed.     

Volumetric Properties of Aqueous Solutions of Cyclohexylsulfamic Acid

The mean apparent molar volume of cyclohexylsulfamic acid has been determined from the density data of aqueous solutions up to a molality of 0.540 mol⋅kg⁻¹ and at 293.15, 298.15, 303.15, 313.15, and 323.15 K. The mean apparent molar volume of the acid was divided into contributing ionic and molecular apparent molar volumes. The limiting apparent molar volume of the molecular acid amounts to (131.69± 0.02) cm³⋅mol⁻¹ and the limiting apparent molar expansibility to (0.130± 0.003) cm³⋅mol⁻¹⋅K⁻¹ at 298.15 K. From the limiting ionic and molecular apparent molar volumes the limiting volume change of ionization of cyclohexylsulfamic acid was calculated. A value of −7.76 cm³⋅mol⁻¹ was evaluated at 298.15 K. The temperature dependence of the volume change of ionization amounts to −(0.018± 0.009) cm³⋅mol⁻¹⋅K⁻¹. From the density data the coefficient of thermal expansion of the investigated solutions was calculated and from this the mean apparent molar expansibility of cyclohexylsulfamic acid was derived.     

Solubility and hydrolysis of lutetium at different [Lu<Superscript>3+</Superscript>]<Subscript>initial</Subscript>

Solubility product (Lu(OH)_3(s)⇆Lu³⁺+3OH⁻) and first hydrolysis (Lu³⁺+H₂O⇆Lu(OH)²⁺+H⁺) constants were determined for an initial lutetium concentration range from 3.72·10⁻⁵ mol·dm⁻³ to 2.09·10⁻³ mol·dm⁻³. Measurements were made in 2 mol·dm⁻³ NaClO₄ ionic strength, under CO₂-free conditions and temperature was controlled at 303 K. Solubility diagrams (pLu_aq vs. pC _H) were determined by means of a radiochemical method using ¹⁷⁷Lu. The pC _H for the beginning of precipitation and solubility product constant were determined from these diagrams and both the first hydrolysis and solubility product constants were calculated by fitting the diagrams to the solubility equation. The pC _H values of precipitation increases inversely to [Lu³⁺]_initial and the values for the first hydrolysis and solubility product constants were log₁₀ β* _Lu,H = −7.92±0.07 and log₁₀ K*_sp,Lu(OH)3 = −23.37±0.14. Individual solubility values for pC _H range between the beginning of precipitation and 8.5 were S _Lu3+ = 3.5·10⁻⁷ mol·dm⁻³, S _Lu(OH)2+ = 6.2·10⁻⁷ mol·dm⁻³, and then total solubility was 9.7·10⁻⁷ mol·dm⁻³.     

The Effect of Temperature on the Equivalent Conductivities and Ion-Association Constants of Some Tris-(ethylenediamine)chromium(III) Complexes in N,N-dimethylformamide and N,N-dimethylacetamide

The equivalent conductivities of tris-(ethylenediamine)chromium complexes, [Cr(en)₃]X₃ (where X⁻= Cl⁻, Br⁻, I⁻; en = ethylenediamine) were measured as functions of temperature (278.15 to 328.15 K) and concentration [(1.948 ×10⁻⁴ to 10.728 ×10⁻⁴ mol⋅dm⁻³) and (2.282 ×10⁻⁴ to 11.246 ×10⁻⁴ mol⋅dm⁻³)] in N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC), respectively. Equivalent conductivity values for [Cr(en)₃]X₃ in DMF were found to be higher than those in DMAC. The conductivity data were analyzed with the Robinson-Stokes equations. For [Cr(en)₃]X₃, the limiting equivalent ionic conductivities of [Cr(en)₃]³⁺ and the ion-association constants (K _A) of the ion-pair between [Cr(en)₃]³⁺ and the monovalent halide anions were determined in DMF and DMAC. The values of K _A for three complex salts in DMF were higher than those in DMAC. This can be ascribed to an increase of the ion-association constants with a decrease of the relative permittivity of the solvents. The values of K _A at 298.15 K decreased in the order Cl⁻> Br⁻> I⁻ in DMF and Cl⁻> I⁻> Br⁻ in DMAC. The K _A values for [Cr(en)₃]Cl₃ increased with increasing temperature in both DMF and DMAC. For [Cr(en)₃]X₃(X⁻= Br⁻, I⁻) in both solvents, this indicates increasing disorder occurs with increasing temperature. Thermodynamic parameters (standard Gibbs energy, enthalpy and entropy changes) were determined from the temperature dependence of K _A in DMF and DMAC. These parameters were inter-compared in their dependences on temperature and solvent.     

Natural radioactivity in rocks of the Modane–Aussois region (SE France)

The activity concentrations of ⁴⁰K, ²³²Th, and ²³⁸U in the characteristic rocks of the Modane-Aussois region (Western Alps, France) were determined using an HPGe gamma-ray spectrometry system. The activity concentrations of ⁴⁰K varied from 18 Bqkg⁻¹ (limestone dolomite) to 392 Bqkg⁻¹ (calcschist), while those of ²³²Th varied from 0.7 Bqkg⁻¹ (limestone dolomite) to 18 Bqkg⁻¹ (calcschist). The activities associated with ²³⁸U ranged from 9 (quartzite) to 29 Bqkg⁻¹ (dolomite). In the investigated rock samples, concentrations of ²³⁸U (ppm) and ⁴⁰K (%) had a strong negative correlation.     

Determination of the chemical forms of iodine with IC-ICP-MS and its application to environmental samples

An online analytical system using ion chromatography (IC) followed by inductively coupled plasma mass spectrometry (ICP-MS) was developed for the separate determination of I⁻ and IO₃⁻ in aqueous solutions with a detection limit 0.1–1 μg 1/1. The total iodine concentration was also directly determined by ICP-MS. Iodine in several environmental samples (i.e., rain, river water, brine, and soil solution) was successfully determined with information on its chemical form. The release of I⁻ into soil solution with decreasing Eh was observed in an incubation experiment with flooded soil. An iodine form other than I⁻ and IO₃⁻ was observed in several environmental samples.     

Redox reactions of 2-hydroxy pyridine: A pulse radiolysis study

Rate constants for reactions of 2-pyridinol with one electron reductants, such ase _aq ⁻ and H atoms and one-electron oxidants, viz. OH, N₃, Br ₂ ⁻ , C1 ₂ ⁻ and O⁻ have been determined at different pH values using the pulse radiolysis technique. From the corrected absorption spectra of the product transient species, the extinction coefficients of these species at their respective absorption maxima have been determined. The kinetics of decay of these transients have been investigated. ThepK _a values of transients formed bye _aq ⁻ and OH radical reactions have been estimated to be 7.6 and 3.5 respectively. Rate constants for electron transfer from semireduced 2-pyridinol to different electron acceptors have been determined.     

Catalytic effect of cuprous ions on the thermal decomposition of 3,3,6,6-tetramethyl-1,2,4,5-tetraoxane in methanol solution

Thermal decomposition of 3,3,6,6-tetramethyl-1,2,4,5-tetraoxane was examined in methanol solution (1.69×10⁻² M) containing cuprous ions (5.05×10⁻⁷ M) in the temperature range from 130 to 166°C using UV spectroscopy as analytical method. The ion-catalyzed reaction follows first-order kinetics with respect to the peroxide and added cuprous ions. The temperature effect on the rate of thermal decomposition of the title compound was described by the corresponding Arrhenius equations, and its stability in solution was estimated on a quantitative level. The activation parameters of the initial step of decomposition of 3,3,6,6-tetramethyl-1,2,4,5-tetraoxane were determined (ΔH ^≠ = 14.7±0.8 kcal mol⁻¹; ΔS ^≠ = −38.9±1.4 cal mol⁻¹ K⁻¹; ΔG ^≠ = 31.0±0.8 kcal mol⁻¹). Electron-transfer mechanism was proposed for the reaction under study. The text was submitted by the authors in English.     

Synthesis,molecular structure,non-isothermal decomposition kinetics and adiabatic time to explosion of 3,3-dinitroazetidinium 3,5-dinitrosalicylate

The title compound 3,3-dinitroazetidinium (DNAZ) 3,5-dinitrosalicylate (3,5-DNSA) was prepared and the crystal structure has been determined by a four-circle X-ray diffractometer. The thermal behavior of the title compound was studied under a non-isothermal condition by DSC and TG/DTG techniques. The kinetic parameters were obtained from analysis of the TG curves by Kissinger method, Ozawa method, the differential method and the integral method. The kinetic model function in differential form and the value of E _a and A of the decomposition reaction of the title compound are f(α)=4α^3/4, 130.83 kJ mol⁻¹ and 10_13.80s⁻¹, respectively. The critical temperature of thermal explosion of the title compound is 147.55 °C. The values of ΔS ^≠, ΔH ^≠ and ΔG ^≠ of this reaction are −1.35 J mol⁻¹ K₋₁, 122.42 and 122.97 kJ mol⁻¹, respectively. The specific heat capacity of the title compound was determined with a continuous C _p mode of mircocalorimeter. Using the relationship between C _p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic time-to-explosion) was obtained.     

Preconcentration and Voltammetric Determination of the Antihypertensive Doxazosin on a C8 Modified Carbon Paste Electrode

 An electrochemical study of the doxazosin oxidative process at carbon paste electrodes using different voltammetric techniques has been carried out. The process is irreversible and controlled by adsorption, giving rise to an oxidation wave around 1.0 V in citric acid-citrate buffer (pH 3.0). A mechanism based on the oxidation of the amine group is postulated. Two methods based on adsorptive stripping (AdS) of doxazosin at the C₈-modified carbon paste electrode (C₈-MCPE), before its voltammetric determination, are studied, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. By means of AdS-DPV and C₈-MCPE, doxazosin can be determined over the 1.0 × 10⁻⁹ to 3.0 × 10⁻⁸ mol L⁻¹ range with a variation coefficient of 2.2% (2.0 × 10⁻⁸ mol L⁻¹) and a limit of detection of 7.4 ×10⁻¹⁰ mol L⁻¹. If AdS-SWV is used, a linear range from 1.0 × 10⁻⁹ to 4.0 × 10⁻⁸ mol L⁻¹ is obtained, the variation coefficient being 2.8% (2.0 × 10⁻⁸ mol L⁻¹, and the limit of detection reached 7.7 × 10⁻¹⁰ mol L⁻¹. The AdS-DPV procedure was applied to the determination of doxazosin in urine and formulations. Received March 13, 1999. Revision December 23, 1999.     

The kinetics of hydroxyl radical reactions with cyclopropane and cyclobutane

A laser flash photolysis/resonance fluorescence investigation has been carried out to study the kinetics of the overall reactions OH + cyclopropane (1) and OH + cyclobutane (2) in the temperature range 298–490 K and at 298 K, respectively. The following kinetic parameters have been determined: k₁ =(3.9 ±0.6) 10⁻¹²exp- (2.2 ± 0.1)kcal mol⁻¹/RT molecule⁻¹cm³s⁻¹, k₂(298 K) = (17.5 ± 1.5)10⁻¹³molecule⁻¹ cm³s⁻¹.     

Determination of Antioxidants and Preservatives in Cosmetics by SPME Combined with GC–MS

A rapid and simple procedure for the determination of antioxidants and preservatives in cosmetics has been developed utilizing solid-phase microextraction combined with GC–MS. A silica fiber coated with polyacrylate provided the highest extraction efficiency. Detection limits in the range from 0.4 to 8.5 ng mL⁻¹ were obtained. Linearity is over a wide range from 1 to 2,000 ng mL⁻¹ with a relative standard deviation under 16%. Cosmetic from a local supermarket were analysed for antioxidants and preservatives to demonstrate the effectiveness of the proposed method. The concentration of antioxidants and preservatives determined was 20–1,218 μg g⁻¹ for methylparaben and 5–3,779 μg g⁻¹ for propylparaben.     

Vertical inventories and fluxes of <Superscript>210</Superscript>Pb, <Superscript>228</Superscript>Ra and <Superscript>226</Superscript>Ra at southern South China Sea and Malacca Straits

Inventories and fluxes of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were determined in sediment cores collected at nine stations covering of the southern South China Sea and Malacca Straits with the thickness of water column between 42 and 83 m depth. The inventories of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were calculated range from 0.15–2.55 Bq cm⁻², 0.05–0.40 Bq cm⁻² and 6.83–83.63 Bq cm⁻², meanwhile the fluxes ranged from 0.005–0.079 Bq cm⁻² yr⁻¹, 0.009–0.048 Bq cm⁻² yr⁻¹ and 0.003–0.037 Bq cm⁻² yr⁻¹, respectively. The results show that the highest inventories and fluxes for ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were found at station WC 01 and EC 05. Because there are additional sources of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra, where water transport will brings more dissolved isotopes, influence of the transportation and deposition of suspended particles, fast rate of regeneration and greater production of those radionuclides and others.     

Comparative study of Cl<Superscript>−</Superscript>, Br<Superscript>−</Superscript>, and I<Superscript>−</Superscript> ions adsorption from dimethyl formamide at Hg- and Ga-electrodes

The adsorption of Cl⁻, Br⁻, and I⁻ ions from their 0.1 M solutions in dimethyl formamide at renewable liquid Hg- and Ga-electrodes was studied under similar experimental conditions by the differential-capacitance and jet-electrode methods. The data obtained points out to a strong effect of the metal nature on adsorption parameters and the halogenide-ion surface activity series. The halogenide-ion surface activity at the Hg-electrode increased in the following sequence: Cl⁻ < Br⁻ < I⁻; at the Ga-electrode, in the reverse sequence: I⁻ < Br⁻ < Cl⁻. The results are explained qualitatively in terms of the Andersen-Bockris model. It follows from the obtained data that (1) the free energy of the metal-halogenide-ion interaction increases in the following sequence: I⁻ < Br⁻ < Cl⁻; (2) the free energy of the Ga-halogenide-ion interaction exceeds that of the Hg⁻halogenide-ion interaction; and (3) the difference of the Cl⁻, Br⁻, and I⁻ ions interaction with the metals increased significantly when passing from Hg⁻ to Ga-electrode.     

Simultaneous ion chromatographic determination of selenium and metal ions in waters at trace level

Summary An ion-chromatographic procedure is described for the determination of selenium (VI) at μg L⁻¹ level in the presence of anions and heavy metal ions. Maximum permissible concentrations and effects from each interfering substance were investigated for the Se concentration range 12.5–1,000 μg L⁻¹. The method, optimized for the detection of SeO ₄ ²⁻ , gives results suitable for speciation analysis. Total selenium can be determined after complete conversion to selenate ion by oxidation with KMnO₄. The detection limit of selenium is 4.8 μg L⁻¹ (0.96 ng for 200 μL sample). Paper presented at the 41st Pittsburgh Conference, New York, March 5–9, 1990.