The aggregation ofn-dodecanephosphonic acid in water

Several techniques were employed to study the aggregation ofn-Dodecanephosphonic Acid (DPA) in water. At 22°C, the solubillity of DPA increases, probably due to the formation of small premicellar aggregates. The CMC is (5.4±2.4) ×10^–4 mol·dm^–3 and the solubility reaches the CMC value at 26°C. At 30°C and at a concentration of about 9×10^–3 mol·dm^–3, a lamellar mesophase appears. Both micelles and liquid crystal lamellae are almost uncharged. Their polar heads have strong hydrogen bonds between them. The ionization of DPA molecules in micelles and mesophase structures is strongly reduced in comparison with monomerically dissolved molecules.     

Supported liquid membrane extraction of W(VI) ions using tri-n-octylamine as carrier

Study of the extraction of W(VI) ions using supported liquid membrane has been carried out. The carrier used for this metal ion transport, is tri-n-octylamine (TOA) dissolved in xylene. The liquid was supported in microporous polypropylene film. The parameters studied are effect of carrier concentration in the membrane, acid concentrations in the feed solution, concentration of stripping agent on transport of W(VI) ions and of temperature on the transport properties of these supported liquid membranes. The optimum conditions of transport for these metal ions determined are, TOA concentration, 0.66 mol·dm^–3 (TOA); HF concentration in the feed solution, 0.01 mol·dm^–3 and concentration of NaOH used as stripping agent 2.5 mol·dm^–3. The maximum flux and permeability determined under optimum conditions are 3.06·10^–5 mol·m^–2·s^–1 and 8.44·10^–11 mol· ·m²·s^–1 at 25±2°C and 4.21·10^–5 mol·m^–2·s^–1 and 11.55·10^–11 mol·m²·s^–1 at 65°C, respectively. The diffusion coefficients for the metal ion carrier complex in the membrane have also been determined. Under the optimum conditions the value for the metal ion carrier complex is 0.14·10^–11 mol·m²·s^–1. Mechanism of transport and the complex formed in the presence of HF have also been discussed. The transport process involves two carrier amine molecules and two protons.     

Adsorptive Voltammetric Study of Thorium–Alizarin Complexon Complex at a Carbon Paste Electrode

A new sensitive adsorptive voltammetric procedure is described for trace measurement of thorium. It is based on the cathodic stripping peak of the thorium–alizarin complexon (ALC) complex at a carbon paste electrode (CPE). The complex of Th(IV) with alizarin is adsorbed at a CPE in a mixed buffer solution (pH 5.0) which consists of 0.1mol·L^–1 sodium acetate and 0.04mol·L^–1 potassium biphthalate, yielding a sensitive cathodic voltammetric peak corresponding to the reduction of alizarin in the complex at –0.57V (vs. SCE). The second-order derivative peak current of the complex is linearly dependent upon the concentration of Th(IV) over the range of 3.0×10^–9 8.0×10^–7mol·L^–1. The detection limit is 1.0×10^–9mol·L^–1 for 180s accumulation. The molar ratio of each component in the complex was estimated as n_Th(IV):n_ALC=1:1 by a continuous variation method. The electrode processes of the Th(IV)–alizarin complex at a CPE were investigated. The procedure was successfully applied to the trace determination of thorium in ore and clay samples.     

Nitric acid transport across TBP—Kerosene oil supported liquid membranes

HNO₃ transport across tri-n-butyl phosphate kerosene oil supported liquid membrane with or without uranyl ion transport has been studied. Parameters studied are the effect of TBP in the membrane, nitric acid in the feed solution and nitrate ion concentration in the feed solution. The flux of protons for 1 to 10 mol·dm^–3 HNO₃ solution is in the range of (0–25)·10^–4 mol·m^–2·s^–1 and for the TBP concentration range of 0.359 to 3.59 mol·dm^–3, the flux determined is (8.9 to 22)·10^–4 mol·m^–2·s^–1. From the experimental data and using theoretical equations the complex under transport through the membrane appears to be 2TBP·HNO₃ both in the presence and absence of uranyl ions. The diffusion coefficient for H⁺ ions through the membrane as a function of TBP concentration varies from (53 to 6)·10^–12 m²·s^–1, based on experimental flux and permeability data. The values of this coefficient supposing 2TBP·HNO₃ as diffusing species, based on viscosity data and theoretical estimation varies from (82.50 to 3.30)·10^–12 m²·s^–1. The value of distribution coefficient varies in the reverse direction from 0.06 to 1.46 at the same TBP concentration.     

Extraction of Pd(II) ions using tri-n-octylamine xylene base supported liquid membranes

Membranes, based on tri-n-octylamine (TOA) xylene liquid, supported in hydrophobic microporous films have been used to study the transport of Pd(II) ions, after extraction into the membrane. Various parameters, such as the effect of hydrochloric acid concentration in the feed solution, TOA concentration in the membrane phase, effect of stripping agent like nitric acid concentration, and temperature on the flux of Pd(II) ions across the liquid membranes have been investigated. The optimum conditions of transport for these metal ions determined are, TOA concentration, 1.25 mol·dm^–3, HCl concentration in the feed solution, 5 mol·dm^–3, and concentration of nitric acid used as a stripping, agent 5 mol·dm^–3. The maximum values of the flux and permeability determined under the optimum condition are 23·10^–6 mol·m^–2·s^–1 and 2.40·10³ m²·s^–1 at 25°C. The results obtained have been used to elucidate the mechanism of palladium transport.     

Transport of titanium(IV) ions across di-2-ethylhexylphosphoric acid-CCl4 supported liquid membranes

Transport study for Ti(IV) ions using di-2-ethylhexylphosphoric acid (D2EHPA) (carrier)-CCl₄ (diluent) liquid supported membrane in microporous polypropylene hydrophobic film has been performed. The parameters studied are effects of carrier, H₂SO₄, stripping agent (NH₄F) concentrations and temperature variation on flux and permeability coefficients of the metal ion. The optimum concentrations of transport found are 2.04 mol·dm^–3 D2EHPA, 1.0 mol·dm^–3 H₂SO₄ in the feed and 1 mol·dm^–3 NH₄F as stripping agent. The maximum flux and permeability coefficient determined are 1.32·10^–5 mol·m^–2·s^–1 and 8.02·10^–12 mol·m^–2·s^–1, respectively. The transport of this metal ion is increased with increase in temperature. The mechanism of transport appears to be based on coupled counter ion transport phenomenon.     

Kinetik der Entstehung des Zinktartrats

Zusammenfassung Aus potentiometrischen Daten wurde die Konstante der Entstehungsgeschwindigkeit des Zinktartrates bei 18° berechnet. Ihr durchschnittlicher Wert beträgt 1,3·10² mol·min^–1 und der Wert der Zerfallsgeschwindigkeitskonstante beläuft sich im Durchschnitt auf 7,5·10^–2 mol·min^–1.     

The New Fluorescence Enhancement System Eu<Superscript>3+</Superscript>-ARADE-HMTM-Al<Superscript>3+</Superscript> and its Analytical Application

A new bis-Schiff base ligand, N,N-bis-(4-N-aminothiourea-2-amylidene)-4,4-diaminodiphenyl ether (ARADE), was synthesized. Its complex with Eu³⁺ in DMF emits the intrinsic fluorescence of Eu³⁺. The fluorescence intensity of the Eu³⁺-ARADE system was enhanced about 60-fold by the addition of hexamethylene tetramine (HMTM) and potash alum. This is a new fluorescence enhancement phenomenon. The excitation and emission wavelengths are 375nm and 615nm, respectively. Under optimal conditions, the fluorescence intensities vary linearly with the concentration of Eu³⁺ in the range of 7.8×10^–9–1.75×10^–5mol·L^–1 with a detection limit of 5.2×10^–9mol·L^–1, or with the concentration of Al³⁺ in the range of 3.1×10^–7–9.7×10^–5mol·L^–1 with a detection limit of 2.7×10^–7mol·L^–1. The interferences of some rare earth metals and other inorganic ions were described. This method was applied to the determination of Eu³⁺ in high purity yttrium oxide and the analysis of Al³⁺ in alloy steel standard samples. The mechanism of fluorescence enhancement was also studied.     

Solubility of particulate cadmium sulfide at pH=1–14: A radiotracer study

Cadmium sulfide particles were prepared by precipitation from acid solution. A radiotracer technique with¹⁰⁹Cd was applied to measure the solubility of cadmium sulfide at various pH's. Filtration, centrifugation, ultracentrifugation, and dialysis were used to separate the particles from the solution. Only the last two techniques proved to be successful. The solubility of cadmium sulfide in water (pH=7) is found to be: 7.9·10^–5 mol·l^–1 in contrast with the literature value of 9.0·10^–6 mol·l^–1. At low pH (1–4), the solubility agrees fairly well with the solubility calculated on the basis of generally accepted values for the solubility product and for the various complex formation constants, while at high pH (4–14) the solubility is higher than expected.     

Hierarchical Unfolding of Mj HSP16.5

Mj HSP16.5 is a small heat shock protein (sHSP) from the hyperthermophilic methanoarchaeon, Methanococcus jannaschii (Mj), which lives at the environment of high temperature up to 94 °C. The structural data showed that Mj HSP16.5 was a 24-mer that formed a hollow sphere with octahedral symmetry. Mj HSP16.5 was very stable at pH 7 that it maintained the 24-mer structure even at 85 °C. In the present study, we investigated the unfolding process of Mj HSP16.5 in the presence of denaturants using several techniques, including circular dichroism (CD), dynamic light scattering (DLS), fluorescence spectroscopy, and size exclusive chromatography (SEC). We found that 8 mol·L⁻¹ urea had no obvious effect on the structure of Mj HSP16.5 at pH 7. The unfolding of Mj HSP16.5 at pH 7 in the presence of guanidine hydrochloride (GdHCl) showed hierarchical behavior. Three significant transitions were observed around 2.0, 3.0, and 6.0 mol·L⁻¹ GdHCl at pH 7. ANS (8-anilino-1- naphthalenesulfonic acid) titration results showed that the binding ability of Mj HSP16.5 to ANS decreased gradually as the concentration of GdHCl increased until around 2.0 mol·L⁻¹ GdHCl, indicating surface hydrophobic area change, and this first transition was companioned with precipitation of Mj HSP16.5. Acrylamide quenching of fluorescence showed that the Stern-Volmer constant changed at about 3.0 mol·L⁻¹ GdHCl, indicating changes of the dimeric interface, and this phase transition was companioned with oligomeric state change from 24-mer to small oligomers (4-mer to 8-mer). The last unfolding phase started around 5.0 mol·L⁻¹ GdHCl, with a midpoint of 6.1 mol·L⁻¹ GdHCl, and Mj HSP16.5 was completely unfolded at 7.0 mol·L⁻¹ GdHCl. We also found that Mj HSP16.5 could be quite easily unfolded at pH 3, where it could be completely unfolded in 4.0 mol·L⁻¹ GdHCl.     

Separation of cerium and europium by extraction with tributyl phosphate and di(2-ethylhexyl)phosphoric acid in n-alkane from nitrate solutions

The following extraction systems have been studied: (Ce³⁺+Eu³⁺) (NO₃)-(EDTA, DCTA, DTPA)/TBP in n-alkane and (Ce³⁺+Eu³⁺)(NO₃)/DEHPA in n-alkane at concentration ratios as follows: [Ce³⁺]=trace –1 mol·dm^–3, [Eu³⁺]=trace –0.1 mol·dm^–3. [TBP]=(0.183–1.83) mol·dm^–3, [DEHPA]=(5·10^–3–0.1) mol·dm^–3, [(H, Na)NO₃]=(0.1–6) mol·dm^–3, [Eu³⁺]: [EDTA, DCTA, DTPA]=11–110. The initial concentration of Eu³⁺ in aqueous phase in the extraction system containing a mixture of Ce³⁺ and Eu³⁺ was trace, 1% and 10% compared with the Ce³⁺ concentration. The distribution of the elements between the phases was observed radiometrically using¹⁴¹Ce,¹⁵²Eu and¹⁵⁴Eu. The results are documented by the distribution ratios D_Ce, D_Eu and separation factor =D_Eu/D_Ce as functions of variable parameters of the systems.     

Elaboration of ZnO Thin Films with Preferential Orientation by a Soft Chemistry Route

Microcrystalline ZnO films presenting well-defined and tunable orientation were obtained by spin coating of alcoholic sols by two different approaches, based on controlled hydrolysis-condensation of Zn-ethanolamine complexes. As-deposited films are formed by amorphous zinc oxide-acetate submicronic particles, which are transformed into oriented ZnO after thermal treatment. The orientation of ZnO depends on the synthesis method, and the solvent. While in ethanol and [Zn] = 0.05 mol·L^–1, films consist of rectangular platelets oriented with the (100) planes parallel to the substrate (a//n), the orientation of the particles changes to (c//n) for systems in 2-methoxyethanol (2-ME) and [Zn] = 0.75 mol·L^–1. A study of chemical factors that influence the orientation (precursor, solvent, MEA/Zn ratio, concentration, coating parameters, heat treatment) is presented.     

Spectrofluorimetric determination of clioquinol in pharmaceutical preparations

Summary The absorption spectrum of the nitrate radical (NO₃) in aqueous solution and the kinetic of the reactions with Cl^– and OH^– have been determined using laser-spectrometric techniques. The maximum absorption was found at 635 nm with a decadic absorption coefficient of =(530±110) l/mol·cm. At 298 K rate constants of k₁=(1.0±0.2)·10⁷ l/mol·s for the reaction with chloride and of k₂=(8.2±0.9)·10⁷ l/mol·s for the reaction with hydroxide were obtained.     

Determination of thorium by adsorptive type chemically modified electrode with a polycomplex system

A preconcentration and determination method for thorium in aqueous solution with a tri-n-octylphosphine oxide modified glassy carbon electrode is proposed. In the presence of 2-thenoyltrifluoroacetone, thorium in NaAc-HAc supporting electrolyte is preconcentrated on a modified rotating disk electrode, and a highly sensitive reduction peak is obtained by cathodic stripping voltammetry at –1.10 V versus Ag/AgCl. A linear response of reduction peak height and concentration is observed for 1.15×10^–9–1.44×10^–8 mol·1^–1 of thorium and the detection limit is 1.0×10^–9mol·1^–1. It is very selective and sensitive, with a standard deviation of 3.4% and a recovery of 90–110%.     

Electron irradiation studies on ammonium molybdophosphate

Ammonium molybdophosphate (AMP) was irradiated with electrons up to a dose of 1 MGy. X-ray diffraction patterns and FT-IR of irradiated and control AMP samples were recorded. Uptake of¹³⁷Cs from nitric acid in the range of 0.2 to 10 mol·dm^–3 was estimated by a batch equilibration technique. AMP undergoes perceptible changes in its physico-chemical characteristics on irradiation with electrons. Uptake of¹³⁷Cs from nitric acid by irradiated AMP was nearly the same as the control AMP in the nitric acid concentration range of 6 to 10 mol·dm^–3 and relatively higher in the range of 0.2 to 6 mol·dm^–3. The results are discussed in terms of available information on the physicochemical properties of 12-heteropoly acids and their salts.     

Transport study of V(V), Zn(II) and Be(II) using supported liquid membranes

V(V), Zn(II) and Be(II) have been studied to test oxine and tri-n-butylphosphate (TBP) as carriers for transport through supported liquid membranes in polypropylene film. All the three types of ions can be passed through such membranes using oxine in case of V(V) and TBP in case of Zn(II) and Be(II). Maximum flux of metal ions has been observed from 0.01M H₂SO₄ for V(V) (3.22·10^–6 mol·m^–2·s^–1) and 2M HCl containing 3M CaCl₂ for Zn(II) solution (1.4·10^–6 mol·m^–2·s^–1). Low flux was observed in case of Be(II) since the membrane was affected by sulphocyanide group and did not remain hydrophobic. Mechanism of transport for these metal ions have been proposed separately. Distribution coefficient data for V(V) have also been evaluated to determine theoretical values of the permeability coefficient, and compared with experimental values.     

Spectrofluorimetric Assay of Cationic Surfactants by Fluorescence Quenching of 9-Anthracenecarboxylic Acid

A new simple, selective and sensitive fluorescence quenching method was developed to determine cationic surfactants with the 9-anthracenecarboxylic acid (ACA). The fluorescence intensity of ACA was decreased by addition of trace amounts of cationic surfactants. Under optimum conditions, the ratio of fluorescence intensity in the absence and presence of cationic surfactants was proportional to the concentration of cationic surfactants over the range of 0.3–4.5 × 10⁻⁵ mol L⁻¹ for cetylpyridinium chloride (CPC) and 0.4–6.0 × 10⁻⁵ mol L⁻¹ for cetyl trimethyl-ammonium bromide (CTAB). The detection limits are 1.0 × 10⁻⁶ mol L⁻¹ for CPC and 1.2 × 10⁻⁶ mol L⁻¹ for CTAB, respectively. Based on this approach, this paper presents a new quantitative method for cationic surfactants assay.     

Study on the fluorescence system Be-rutin-SDS-Triton X-100 and the determination of rutin

Summary It was found that rutin forms a fluorescent complex with Be²⁺, the fluorescence intensity of which can be increased thirty-one times in a mixed medium of sodium dodecyl sulfonate (SDS) and Triton X-100. A linear relationship is obtained between the fluorescence intensity and the rutin concentration in the range of 1.2×10^–6 to 4.8×10^–5 mol·l^–1. The detection limit is 5.9×10^–7 mol·l^–1. Rutin traces were determined in drugs using the standard addition method. The luminescence mechanism of the system is discussed.     

Sorption of europium on zirconium oxide from aqueous solutions

Sorption of europium on zirconium oxide has been studies as a function of shaking time, concentration and nature of electrolyte. The effect of initial europium concentration and the amount of adsorbent has been investigated in the range from 6.6·10^–10 to 6.6·10^–8 mol·dm^–3 and between 10 to 200 mg of the oxide. Maximum sorption (>99.8%) from pH 10 buffer and low sorption (<3%) was observed from 0.01 mol·dm^–3 nitric or perchloric acid solution. Citrate, sulfate, EDTA and carbonate reduced the sorption significantly. Under optimal conditions Ag(I), Cs(I), Tc(VII), Sb(V), Cu(II), Nd(III), Fe(III), and especially Nd and Fe showed low distribution coefficients. The data followed both Dubinin-Radushkevich and Langmuir-type isotherms. The mean free energy, of sorption was evaluated to be 10.1 kJ mol^–1 and the sorption capacity was found to be 22.2 mmol g^–1, using the Dubinin-Radushkevich isotherm.     

Precipitation separation of strontium and calcium from acidic solutions using crown ether and tungstosilicic acid

Strontium forms a compound of composition (SrL)₂A·nH₂O with low solubility (5.0·10^–6 mol Sr·dm^–3) in the presence of 18-crown-6 (L) and tungstosilicic acid (H₄A) in acid media, as has been found by radiometric precipitation titration. Formation of the compound with limited solubility was used for separation of strontium and calcium from 1 mol·dm^–3 HCl. It is possible to separate strontium in the range from trace to 6 mmol·dm^–3 in the presence of calcium with its concentration up to 0.2 mol ·dm^–3 and the recovery determined was 95% of Sr and 5% Ca or 90% of Sr and 4% Ca, respectively. The ratio of Sr/Ca depends on the stability constants ratio of metal-L (⊃_SR/⊃_ca) in the case of gradual addition of L. Potassium up to the concentration of 0.05 mol·dm^–3 does not influence recovery of strontium.