Thermoelectric power studies on MgO-stabilized β″-alumina

A study of the temperature dependence of thermopower is known to yield auxiliary information about the electronic conductivity of a mixed conductor. In light of the above, thermoelectric power (TEP) measurements were made on MgO-stabilized β″-alumina over the temperature range from 773 to 1223 K under conditions of different sodium activities in the ambient in order to substantiate the existing information on the electronic conductivity of sodium beta alumina (SBA). A mixture of Na _x Si _m O_{2 m + x /2} and SiO₂ in an environment of fixed served as electrodes reversible to Na⁺. The heat of transport obtained using the thermopower data at higher temperatures (973–1223 K) was in fair agreement with the activation energy of electrical conduction determined by other studies like impedance measurements and molecular dynamics simulation. It could be inferred from these results that there is negligible electronic conductivity in SBA under the conditions of measurement. The average TEP for SBA was determined to be 700–800 μV/K and the partial molar entropy of Na⁺ in SBA was found to be ~98 J mol^–1 K^–1. Electronic Publication     

Dioxygen reactivity of laccase

A study was carried out on the dioxygen reactivity of the laccases from Trametes villosa, Rhizoctonia solani, Myceliophthora thermophila, Scytalidium thermophilum, and Coprinus cinereus. At pH 5.5, these laccases showed an apparently constant K _m (about 20–50 μM) for O₂ with either 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) or methyl syringate as the reducing substrate, in contrast to the k _cat , which varied up to 100-fold. O₂ reactivity of the Trametes and Myceliophthora laccases was also studied at various pH and NaF concentrations. The apparent K _m of Trametes and Myceliophthora laccases varied only slightly when pH changed from 3.0 to 8.0 or when the laccases were inhibited by F⁻ at pH 5.5, although the apparent k _cat were more significantly affected by both factors. The dependence of the apparent K _m on the source of laccase, pH, and F⁻ inhibition suggested that the fungal laccases might have a conserved O₂ pocket and that the F⁻ or OH⁻ inhibition might affect the O₂ reduction step (k _cat ) more than the O₂ binding step (K _m ) under steady-state conditions.     

Vacancy Contents in MnZn Ferrites From TG Curves

Expressions for calculating the cation vacancy contents of MnZn ferrites from thermogravimetric curves are presented together with some experimental data. In a single-phase MnZn ferrite synthesized by conventional ceramic procedures, the O₂ evolution accompanying ferrite formation follows the formal equation. Mn²⁺ _σα Zn_σβ Fe³⁺ _2σ(1–γ) [V ]_{σ/4(1–2γ)} O₄ =σ'/σ Mn²⁺ _σ(α–2ϕ) Zn_σβ Fe²⁺ _2σθ Mn³⁺ _2σϕ Fe³⁺ _{2σ(1–γ–θ)} [V ]_{σ/4(1–2γ–3ϕ)} O₄ +σ'φ/2O₂ (g) where α and β denote the MnO and ZnO mole fractions in the primary mixture γ=α+β, θ and ϕ depend on the quantities of Fe²⁺ and Mn³⁺ formed, respectively, φ=θ–ϕ and σ'/σ is a function of the former parameters. Even though the relative amounts of Fe²⁺ /Fe³⁺ and Mn²⁺ /Mn³⁺ remain uncertain, the vacancy content [V ] of the ferrite can be determined because it depends on φ alone, which is related to the change in mass of the sample as the synthesis takes place through the equation φ=(1.5–γ) μ_β /μ_O2 (1–m _f /m _i ) Here, m _i and m _f are the masses of the sample before and after O₂ evolution, μ_B is the formula mass of the ferrite and μ_O2 is the O₂ molar mass. Practically vacancy-free single-phase MnZn ferrite samples were obtained by sintering in air at 1250°C and cooling in pure N₂ . This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of poly(styrene/α-t-butoxy-ω-vinylbenzyl-polyglycidol) microspheres

Polystyrene microspheres with polyglycidol (polyGL) in a surface layer were synthesized in batch radical emulsifier-free emulsion copolymerizations of styrene and surfmers, α-t-butoxy-ω-vinylbenzyl-polyGL macromonomers (VB-polyGL). Macromonomers with number-average molecular weight Mˉ _n=950 (VB-polyGL950) and Mˉ _n=2700 (VB-polyGL2700) were used for these polymerizations. In all syntheses the initial concentrations of styrene and initiator (K₂S₂O₈) were constant. The initial macromonomer-to-styrene ratios were varied from 1.10 × 10⁻³ to 1.64 × 10⁻² mol/mol and from 3.46 × 10⁻⁴ to 3.47 × 10⁻³ mol/mol for VB-polyGL950 and VB-polyGL2700, respectively. The diameters of microspheres obtained were smaller for the syntheses with higher concentrations of macromonomers. Syntheses with VB-polyGL950 yielded microspheres with number-average diameters (Dˉ _n) from 216 to 900 nm and with a bimodal diameter distribution. The number-average diameters of microspheres obtained with VB-polyGL2700 varied from 220 to 650 nm, depending on the initial concentration of macromonomer. Their diameter distributions were monomodal, with a diameter polydispersity parameter (ratio of weight-average and number-average diameters) in the range 1.007≤Dˉ _w/Dˉ _n≤1.022. For each type of microsphere the fraction of polyGL in a surface layer and the surface concentration of sulfate anions were determined. The fraction of polyGL in the surface layer was related to the initial monomer composition in the polymerizing mixture. Adsorption of human serum albumin onto surfaces of some poly(styrene/VB-polyGL) microspheres was up to 10 times lower than for the polystyrene microspheres obtained in a similar emulsifier-free emulsion polymerization of styrene. Received: 26 September 2000/Accepted: 19 February 2001     

Praseodymium β-diketonates and luminescence properties of their solutions

The luminescence intensity of Pr(III) in a series of complexes with alkyl and thienyl fluoroacetylacetone derivatives has been shown to increase not only with an increase in the length of the fluoroalkyl radical but also with the introduction of an oxygen heteroatom into this radical. The luminescence intensity of Pr(III) increases by about two orders of magnitude when a donor ligand (an organic solvent) is introduced into the complex. In some cases, the triplet level of β-diketone become higher due to interligand energy transfer and the Pr(III) luminescence occurs from two emitting levels ¹ D ₂ (the ¹ D ₂ → ³ H ₄ transition, λ_lum = 605 nm) and ³ P ₀ (the ³ P ₀ → ³ H ₆ transition, λ = 612 nm). Heteroleptic Pr(III) β-diketonates have short lifetimes (τ); for example, the lifetime of the Pr(III) complex with thenoyltrifluoroacetone and diantipyrylmethane is shorter than 1 μs. Original Russian Text ? S.B. Meshkova, A.V. Kiriak, Z.M. Topilova, A.M. Andrianov, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 4, pp. 614–619.     

Cloning, expression, and characterization of thermostable region of amylopullulanase gene from Thermoanaerobacter ethanolicus 39E

The bifunctional activities of α-amylase and pullulanase are found in the cloned recombinant amylopullulanase. It was encoded in a 2.9-kb DNA fragment that was amplified using polymerase chain reaction from the chromosomal DNA of Thermoanaerobacter ethanolicus 39E. An estimated 109-kDa recombinant protein was obtained from the cloned gene under the prokaryotic expression system. The optimum pH of the recombinant amylopullulanase was 6.0. The most stable pH for the α-amylase and pullulanase activity was 5.5 and 5.0, respectively. The optimum temperature for the α-amylase activity was 90°C, while its most stable temperature was 80°C. Regarding pullulanase activity, the optimum temperature and its most stable temperature were found to be 80 and 75°C, respectively. Pullulan was found to be the best substrate for the enzyme. The enzyme was activated and stabilized by the presence of Ca²⁺, whereas EDTA, N-bromosuccinimide, and α-cyclodextrin inhibited its bifunctional activities. A malto-2–4-oligosac-charide was the major product obtained from the enzymatic reaction on soluble starch, amylose, amylopectin, and glycogen. A single maltotriose product was found in the pullulan hydrolysis reaction using this recombinant amylopullulanase. Kinetic analysis of the enzyme indicated that the K _m values of α-amylase and pullulanase were 1.38 and 3.79 mg/mL, respectively, while the V _max values were 39 and 98 μmol/(min · mg of protein), respectively.     

Lichenysin

The lipopeptide lichenysin (cyclo-[L-Gln1→D-Leu2→L-Leu3→L-Val4→L-Asp5→D-Leu6→L-Ile7-β-OH fatty acid]) produced by Bacillus licheniformis structurally resembles surfactin from Bacillus subtilis. The main difference is the presence of a glutaminyl residue in position 1 of the peptide sequence in place of glutamic acid in surfactin. This local variation causes significant changes in the properties of the molecule compared to surfactin. Lichenysin has a higher surfactant power, the critical micellar concentration (c.m.c.) being strongly reduced from 220 to 22 μM and a much higher hemolytic activity because 100% hemolysis was observed with only 15 μM instead of 200 μM. Lichenysin is also a better chelating agent because its association constants with Ca²⁺ and Mg²⁺ are increased by a factor of 4 and 16, respectively. This effect is assigned to an increase in the accessibility of the carboxyl group to cations owing to a change in the side chain topology induced by the Glu/Gln exchange. Additionally, the propensity of the lipopeptide for extensive hydrophobic interactions, as illustrated by its low c.m.c., contributes to further stabilization of the cation and an increase in the partitioning of lichenysin into the erythrocyte membrane. Our data support the formation of a lichensyin-Ca²⁺ complex in a molar ratio of 2:1 instead of 1:1 with surfactin, suggesting an intermolecular salt bridge between two lichenysin molecules. Therefore, when Ca²⁺ ions are present in the solution, micellization occurs via a dimer assembly, with a possible long-range effect on the spatial arrangement of the micelles or other supramolecular structures. Finally, among all the surfactin peptidic variants so far known, lichenysin is the one for which the three tested activities are the most substantially improved.     

Electrochemical Behavior of a Gold Electrode Modified with SWNTs/DDAB Films and Its Electrocatalytic Activity Towards Ascorbic Acid

A film of single-wall carbon nanotubes (SWNTs) and didodecyldimethylammonium bromide (DDAB) is prepared by casting a solution of SWNTs and DDAB onto the surface of a gold electrode. The electrochemical behavior of the film is investigated by electrochemical impedance spectroscopy and cyclic voltammetry. In a 0.10 M phosphate buffer solution of pH 7.0, the film-modified electrode gives a pair of redox peaks in cyclic voltamograms, with the anodic and cathodic peak potentials of 0.095 and 0.042 V. The peak currents change linearly with the scan rate at 30–500 mV/s. The modified electrode has an excellent electrocatalytic activity towards the oxidation of ascorbic acid (AA). The catalysis currents are proportional to the AA concentration in the range of 5.0 × 10⁻⁴ to 3.2 × 10⁻² M. The linear-regression equation is i (μA) = 1.2079 + 1.3987 × 10³ c _AA (M), with a correlation coefficient of 0.9995. The detection limit is 2.2 × 10⁻⁴ M (signal-to-noise ratio of 3). The Michaelis-Menten constant (K _m) is 1.0 × 10⁻⁴ M by the Lineweaver-Burk equation. __________ From Elektrokhimiya, Vol. 41, No. 10, 2005, pp. 1193–1199. Original English Text Copyright ? 2005 by Cheng, Jin, Zhang. The text was submitted by the authors in English.     

Functional sulfur amino acid production and seawater remediation system by sterile Ulva sp. (chlorophyta)

Sterile Ulva, which is a macroalga, has the potential to grow stably; therefore, this seaweed is expected to be an efficient resource of functional food containing various nutrients such as sulfur amino acids, proteins, carbohydrates, and minerals. Ulva lactuca was selected from the “Marine Park” in Tokyo Bay, and its growth rate (g-dry/[m²·d]) was measured using model reactors located on the land or on the surface of the sea at Yokohama. The growth rate of U. lactuca was recorded to be approx 20 g-dry/(m²·d), which is estimated to be 10 times greater than that in a natural field in the Marine Park. In addition, this growth rate was higher than that of conventional crops such as corn and rice on a farm or paddy. These data led us to newly design and propose a floating type of labor-efficient U. lactuca production system. d-Cysteinolic acid, which is included in U. lactuca as a major sulfur amino acid, inhibited the Fenton reaction, resulting in suppression of hydroxyl radical production and singlet oxygen. Addition of the sulfur amino acid (1μM) to HepG2 cells markedly decreased the intracellular triglyceride level. Hence, this proposed facility also has the potential for industrial production of a valuable resource for the primary prevention of lifestyle-related diseases using enriched or eutrophied seawater.     

Comparison of the cold vapor generation using NaBH4 and SnCl2 as reducing agents and atomic emission spectrometry for the determination of Hg with a microstrip microwave induced argon plasma exiting from the wafer

A 2.45 GHz low power microwave microstrip plasma (MSP) exiting the wafer and operated with Ar at atmospheric pressure was used for the optical emission spectrometric determination of Hg with the aid of a miniaturized optical fiber spectrometer with a CCD detector and the cold vapor (CV) generation technique using NaBH₄ and SnCl₂ as reductants. The experimental conditions were optimized with respect to the relative intensity of the Hg I 253.6 nm line and its signal-to-background intensity ratio (SBR). So as to understand the results of the optimization experiments, the excitation temperatures as measured from Ar I lines (T _exc) and the electron number densities (n _e) for the Ar MSP loaded with Hg vapors were determined and found to be in the range from 5500 to 6300 K and from 1.4 to 2.0 × 10¹⁴ cm⁻³, respectively. Under the optimized conditions, the detection limit for Hg of the CV-MSP-OES using SnCl₂ as the reducing agent was found to be much lower (0.11 ng mL⁻¹) than in the case where NaBH₄ was used (9 ng mL⁻¹). The linearity range was found to be up to 1 μg mL⁻¹ while the precision was of the order of 0.7–5%. The procedure with SnCl₂ as reductant was used for the determination of Hg at a concentration of 0.2 μg mL⁻¹ in synthetic water samples containing 1 to 4% (m/v) of NaCl with an accuracy of 3% as well as in a solution of the domestic sludge standard reference material (NIST SRM 2781) with a certified concentration for Hg of 3.64 ± 0.25 μg g⁻¹ for which 3.55 ± 0.41 μg g⁻¹ was found. Correspondence: J. A. C. Broekaert, Institut für Anorganische und Angewandte Chemie, Universit?t Hamburg, 20146 Hamburg, Germany     

Crystallochemistry of mercury chalcogenides. IV. Crystalline structure of two polymorphous modifications of the mercury sulfochalcogenide Hg3S2Br1.5Cl0.5

Two modifications of a new mercury sulfohalide of Hg₃S₂Br_2−x Cl_x (x = 0.5) composition have been grown from the gas phase and explored by X-ray structural analysis. The compounds were obtained at an attempt to synthesize an analogue of the rare mineral arzakite Hg₃S₂(Br, Cl)₂ (Br > Cl). The refinement of the crystalline structures of monoclinic (I) and cubic (II) phases (I: a = 17.824(4) Å, b = 9.238(2) Å, c = 10.269(2) Å, β = 115.69(1)°, V = 1523.8(5) ų, space group C2/m, Z = 8, R = 0.0513; II: a = 18.248(2) Å, V = 6076.4(12) ų, space group Pm3ˉn, Z = 32, R = 0.038) has shown that they are polymorphous modifications of the compound of Hg₃S₂Br_1.5Cl_0.5 formula. The monoclinic modification I is isostractural to the synthetic compound α-Hg₃S₂Br₂. Modification II is isostructural to synthetic β-Hg₃S₂Cl₂. In both structures, each atom S has in its surrounding three atoms of Hg forming umbrella-type groups SHg₃ with spaces Hg—S 2.366–2.430 Å and angles HgSHg 95.66–97.60°. SHg₃-fragments are bound by Hg-apices with the formation of isolated cubic groups [Hg₁₂S₈]. Like that in other structures of mercury chalcohalides, the main role in structure-forming of the investigated compounds is played by atoms of halogens creating a cubic sublattice in which radicals Hg—S are arranged. Original Russian Text Copyright ? 2006 by N. V. Pervukhina, S. A. Magarill, D. Yu. Naumov, S. V. Borisov, V. I. Vasil’yev, and B. G. Nenashev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No. 2, pp. 318–323, March–April, 2006.     

Synthesis and crystal and molecular structure of the mixed-ligand coordination compound ZnPhen(n-C4H9OCS2)2

A mixed-ligand complex ZnPhen(n-BuOCS₂)₂ has been synthesized. The structure of the compound was solved by X-ray diffractometry (X8 APEX diffractometer, MoK _α radiation, 4254 F _hkl , R = 0.0448). Triclinic crystals with the parameters a = 9.4464(3) Å, b = 11.0279(4) Å, c = 13.6528(6) Å;α = 106.940(1)°, β = 98.382(1)°, γ = 106.347(1)°; V = 1264.72(8) ų; Z = 2, space group 1. P1ˉ. The structure consists of discrete mononuclear molecules. The polyhedron of the Zn atom is a trigonal bipyramid N₂S₃ formed by coordination of the N atoms of the bidentate Phen molecules and the sulfur atoms of the monodentate and cyclic bidentate xanthate ligands. Dimer assemblies are formed in the structure due to π-π interactions of Phen molecules. Original Russian Text Copyright ? 2006 by R. F. Klevtsova, T. G. Leonova, L. A. Glinskaya, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No. 6, pp. 1189–1194, November–December, 2006.     

Study on interaction between antibiotics and Escherichia coli DH5α by microcalorimetric method

A microcalorimetric technique based on the bacterial heat output was applied to evaluate the influence of antibiotics PIP (Piperacillin Sodium) and composite preparation of PIP and SBT (Sulbactam Sodium) on the growth of E. coli DH5α. The power–time curves of the growth metabolism of E. coli DH5α were studied using a TAM Air Isothermal Microcalorimeter at 37°C. By analyzing the power–time curves, the parameters such as growth rate constants (k), inhibitory ratio (I), the maximum heat power (P _m) and the time of the maximum heat power (t _m) were obtained. The results show that different concentrations of antibiotics affect the growth metabolism of E. coli DH5α. The PIP in the concentration range of 0–0.05 μg mL^–1 has a stimulatory effect on the E. coli DH5α growth, while the PIP of higher concentrations (0.05 –0.25 μg mL^–1) can inhibit its growth. It seems that the composite preparation composed of PIP and SBT cannot improve the inhibitory effect on E. coli DH5α as compared with the PIP.     

Conformation changes in the DNA molecule caused by γ-irradiation of its water ethanol solutions of great ionic strength

The conformation changes in DNA in water ethanol solutions (ethanol content 0–22 wt.%, ionic strength μ = 0.15 M NaCl) exposed to γ radiation (10 Gy and 30 Gy doses) were investigated by low-gradient viscosimetry, birefringence in a flow, circular dichroism (CD), and UV spectrophotometry. For μ = 0.15 M, the volume of intact DNA remained constant over the whole range of alcohol concentrations studied in contrast to water alcohol solutions of lower ionic strength, in which the specific volume of the macromolecule decreased cooperatively at a critical concentration of alcohol corresponding to a structure disturbance of water (C _cr = 16.5 wt.% for ethanol). Inversion of the dependence of the specific volume of DNA on the radiation dose, which was found previously for water alcohol solutions with μ = 0.003 M NaCl, vanished under these conditions. For μ = 0.15 M, the dependence of V _sp of DNA on C _eth had no features at C _eth = C _cr; at C _eth ≥ 1.7 wt.% the volume of the macromolecule did not change after irradiation with doses of up to 40 Gy. This is probably explained by the fact that at high salt concentrations the alcohol loses its influence on the structure of the solvent, and its role in the process of γ irradiation is restricted to interception of the active products of water radiolysis. __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 4, pp. 783–788, July–August, 2007. Original Russian Text Copyright ? 2007 by S. V. P ston, I. M. Zyryanova, Yu. V. Zaichikova, and V. V. Zamotin     

Thermal and Spectral Behaviour of 5-chloro-2-methoxybenzoates of Heavy Lanthanides and Yttrium

5-Chloro-2-methoxybenzoates of heavy lanthanides and yttrium were obtained as di- or tetrahydrates with a metal to ligand ratio of 1:3 and general formula: Ln(C₈H₆ClO₃)₃⋅nH₂O, where n=2 for Ln=Tb, Dy, Y and n=4 for Ln=Ho, Er, Tm, Yb, Lu. The complexes were characterized by elemental analysis, IR and FIR spectra, thermogravimetric studies, X-ray diffraction and magnetic measurements. The carboxylate group appears to be a symmetrical, bidentate, chelating ligand. All complexes are polycrystalline compounds. Their thermal stabilities were determined in air and in nitrogen atmospheres. When heated they dehydrate to form anhydrous salts which next in air are decomposed to the oxides of the respective metals while in nitrogen to the mixtures of carbon and oxides or carbon and oxychlorides of respective metals. The complexes are more stable in air than in nitrogen. The solubilities of yttrium and heavy lanthanide 5-chloro-2-methoxybenzoates in water at 293 K are of the order of 10^–3 mol dm^–3 The magnetic moments of the complexes were determined over the range 77–298 K. They obey the Curie–Weiss law. The values of μ_eff calculated for all compounds are close to those obtained for Ln³⁺ by Hund and Van Vleck. The results indicate that there is no influence of the ligand field of 4f electrons on lanthanide ions and the metal ligand bonding is mainly electrostatic in nature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of t-Butyldimethylsilyl Derivatives of Chlorophenols in the Atmosphere of Urban and Rural Areas in East of France

A method using GC-MS and derivatization with N-(t-butyldimethylsilyl)-N-ethyltrifluoroacetamide (MTBSTFA) was developed for the analysis of 19 chlorophenols compounds in atmospheric samples (gas and particles). Air sampling was carried out using a Hi-Vol sampler with glass fibre filter and XAD-2 resin at a flow rate of 60 m³ h⁻¹. The particle and gas phases were collected separately over a period of 4 h. Samples were Soxhlet extracted, evaporated to dryness under nitrogen and refilled with acetonitrile. 100 mL of these extracts were derivatized with 100 μL of MTBSTFA at 80 °C for 1 h under strong stirring. Sylylated chlorophenols were injected into a GC-MS in splitless mode and quantified as their TBDMS derivatives in the SIM mode. Mass spectral analysis of the derivatives of the 19 compounds studied indicates that the spectra are highly specific showing an ion at [M - 57]⁺ which is useful for structure confirmation or analysis at low levels using selected ion monitoring. Quantification limits varied between 5 μg L⁻¹ and 10 μg L⁻¹ which correspond to 20 pg m⁻³ and 40 pg m⁻³ for 250 m³ of air sampled. This method was successfully applied to atmospheric samples collected simultaneously in winter 2004 in an urban (Strasbourg) and rural (Erstein) areas in east of France.     

Effect of selenium oxidation state on cadmium translocation in chamomile plants

Syntheses and spectral characteristics of cadmium(II) compounds (CdSeO₄, CdSeO₃, and Cd(NCSe)₂(nia)₂) containing selenium in oxidation states (VI), (IV), and (-II) are described. In Cd(NCSe)₂(nia)₂, nicotinamide (nia) and selenocyanate anions are bonded to Cd atom as N-donor monodentate ligands. Nicotinamide is coordinated through the ring nitrogen atom. The effects of these selenium compounds as well as Cd(NCS)₂(nia)₂ on the growth and Cd accumulation in roots and shoots of hydroponically cultivated chamomile plants (cultivar Lutea) were studied. In the applied concentration range (12–60 μmol dm⁻³) Cd(NCS)₂(nia)₂ affected neither the length nor the dry mass of roots and shoots. Other compounds applied at 24 μmol dm⁻³ and 60 μmol dm⁻³ significantly reduced dry mass of roots and shoots. Selenium oxidation state in the cadmium compounds affected Cd accumulation in plant organs as well as Cd translocation within the plants, which was reflected in the values of bioaccumulation (BAF) and translocation factors (S/R). Cd amount accumulated by shoots was lower than that in the roots. The highest BAF values determined for Cd accumulation in shoots were obtained with CdSeO₄. Substitution of S with Se in the Cd(NCX)₂(nia)₂ (X = Se or S) caused an increase of Cd translocation into the shoots. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Electrocatalytic oxidation of dopamine at an ionic liquid modified carbon paste electrode and its analytical application

A room-temperature ionic liquid N-butylpyridinium hexafluorophosphate was used as a binder to construct an ionic liquid modified carbon paste electrode, which was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The ionic liquid carbon paste electrode (IL-CPE) showed enhanced electrochemical response and strong analytical activity towards the electrochemical oxidation of dopamine (DA). A pair of well-defined quasireversible redox peaks of DA appeared, with the redox peaks located at 215 mV (E _pa) and 151 mV (E _pc) (vs. the saturated calomel electrode, SCE) in pH 6.0 phosphate buffer solution. The formal potential (E ^0′) was calculated as 183 mV (vs. SCE) and the peak-to-peak separation as 64 mV. The electrochemical behavior of DA on the IL-CPE was carefully investigated. Under the optimal conditions, the anodic peak currents increased linearly with the concentration of DA in the range 1.0 × 10⁻⁶–8.0 × 10⁻⁴ mol/L and the detection limit was calculated as 7.0 × 10⁻⁷ mol/L (3σ). The interferences of foreign substances were investigated and the proposed method was successfully applied to the determination of DA injection samples. The IL-CPE fabricated was sensitive, selective and showed good ability to distinguish the coexisting ascorbic acid and uric acid.     

Ion chromatographic and spectrometric determination of water-soluble compounds in airborne particulates, and their correlations in an industrial area in Attica, Greece

In the time period from June 2005 to May 2006 in 42 sampling campaigns 84 filter samples of airborne particulate matter, coarse (PM_10–2.5) and fine (PM_2.5), were collected using a Gent stacked filter unit in the coastal industrial area of Aspropyrgos in Attica, Greece. The average PM₁₀ (PM_10–2.5 + PM_2.5) concentration was found to be 66 μg · m⁻³, exceeding more than 1.6 times the annual limit of 40 μg · m⁻³. The samples were analysed for Cl⁻, NO₃ ⁻, SO₄ ²⁻, Ca²⁺, Mg²⁺, Na⁺, K⁺ and NH₄ ⁺ using ion chromatography. The data were compared with results obtained with other spectrometric methods, such as inductively coupled plasma-atomic emission spectrometry, atomic absorption spectrometry, energy dispersive X-ray fluorescence and reflectometry. The determined average ionic content comprised about 44% of the PM₁₀ mass. The ionic composition, as well as the possible matrix compounds in both fractions were evaluated by dividing the sampling period into summer and winter season. In the PM_10–2.5/PM_2.5 fraction in summer time the concentrations of Ca²⁺, Mg₂₊ and NO₃ ⁻ were enriched in the coarse fraction. In winter time all species were enriched in the coarse fraction, especially Ca²⁺, Cl⁻ and NO₃ ⁻. NH₄ ⁺ was constantly higher in the fine fraction in summer as well as in winter time. Factor analysis was applied to obtain correlations between cations and anions leading to matrix compounds in both fractions. From the evaluation of the results obtained, some of the local air pollution sources could be identified. Correspondence: Klaus-Michael Ochsenkühn, Laboratory for Trace Element Studies, Institute of Physical Chemistry, NCSR “Demokritos”, Aghia Paraskevi 15310, Athens, Greece     

Capillary electrophoresis detection scheme for vitamin B1 and vitamin B2 based on the potassium hexacyanoferrate(III) chemiluminescence system

A novel chemiluminescence (CL) detection scheme for the simultaneous determination of vitamin B1 and vitamin B2 has been developed. After being separated by capillary electrophoresis (CE), the analytes were determined by direct CL of vitamin B1 and vitamin B2-potassium hexacyanoferrate(III) (K₃[Fe(CN)₆]) in alkaline aqueous solution. Parameters affecting CE-CL separation and detection, such as the pH value and the concentration of electrolyte and K₃[Fe(CN)₆] were optimized. Vitamin B1 and vitamin B2 are completely resolved with migration times shorter than 5 min. Under the optimal conditions, a linear range from 0.04 to 50, 0.08 to 90 μg mL⁻¹ and a detection limit of 0.01, 0.03 μg mL⁻¹ (signal-to-noise ratio = 3) for vitamin B1 and vitamin B2 respectively, were achieved. The relative standard deviations (R.S.D.) for 0.5 μg mL⁻¹ of vitamin B1 and 0.8 μg mL⁻¹ of vitamin B2 (n = 11) were 2.9 and 3.7%, respectively. The applicability of the method was examined for the analysis of pharmaceutical tablets. Correspondence: Juan Bai, Physical Education and Human Kinesiology Department, University of Science and Technology of Qingdao, Qingdao 266042, China