Sorption of strontium on Slovak bentonites

Sorption of Sr on five Slovak bentonites of deposits has been studied with the use of batch technique. In the experiments there have been used natural, chemically modified and irradiated samples, in three different kinds of grain size. The pH influence on sorption of strontium on bentonites, pH change after sorption and influence of competitive ions have been studied. Distribution ratios have been determined for bentonite–strontium solution system as a function of contact time, pH and sorbate concentration. The data have been interpreted in term of Langmuir isotherm. The uptake of Sr has been rapid and the sorption of strontium has increased by increasing pH. The percentage sorption has decreased with increasing metal concentrations. The pH value after sorption for the natrificated forms of bentonite starts already in the alkaline area and moves to the higher values. For the natural bentonites the values occur in the neutral or in the acidic area. Sorption of Sr has been suppressed by presence of competitive cations as follows: Ba²⁺ > Ca²⁺ > Mg²⁺ > NH₄ ⁺ > K⁺ > Na⁺. By sorption on natrificated samples colloidal particles and pH value increase have been formed. The bentonite exposure as a result of interaction of γ-rays has led to expansion of the specific surface, increasing of the sorption capacity and to the change in the solubility of the clay materials.     

Poly (vinyl chloride) decomposition in solution

Thermal degradation of PVC in various solvents at 180° has been observed to be in the following order: benzonitrite > nitrobenzene > cyclohexanone > dioctyl phthalate > α-bromonaphthalane > decahydronaphthalene. The effect has been explained on the basis of β-eliminations of E₁-type favoured by polar solvents. An inhibition in PVC degradation has been observed in nitrobenzene containing stationary hydrogen chloride gas. The deceleration in degradation by predissolved HCl has been accounted for as a Mass Law effect.     

A new modified conducting carbon composite electrode as sensor for ascorbate and biosensor for glucose

A new carbon-based conducting composite has been developed as electrochemical sensor and biosensor for the amperometric detection of ascorbate and glucose. Electrocatalytic oxidation of ascorbate has been done successfully at unmodified cellulose acetate-graphite composite electrodes, the sensor being highly sensitive, selective and with a low detection limit at 0.0 V vs. SCE and was successfully applied for ascorbate determination in commercial fruit juice samples. An interference free glucose biosensor has also been developed, based on the immobilisation of glucose oxidase by cross-linking with glutaraldehyde on poly (neutral red) modified composite electrodes. The biosensor exhibits a higher sensitivity of 31.5 ± 1.7 µA cm^− 2 mM^− 1 than other carbon-composite-based glucose biosensors, a detection limit of 20.3 µM and a very short response time.     

Sensitive Determination of DNA by Resonance Light Scattering with Pentamethoxyl Red

A novel sensitive method for the determination of nucleic acid (DNA) using the resonance light scattering (RLS) spectra of pentamethoxyl red has been developed. It is based on the effects on the resonance light scattering of Pentamethoxyl Red. The effective factors and the optimum conditions were studied, and the enhanced intensity of RLS is in proportion to the concentration of nucleic acids in the range of 0–2.54 µg mL⁻¹ for ct-DNA, 0–4.54 µg mL⁻¹ for hs-DNA. The limits of detection are 1.1 and 2.1 ng mL⁻¹, respectively. Most foreign substances do not interfere in the determination, and the method has good selectivity and high sensitivity. It has been applied to the determination of DNA in synthetic samples and in real samples with satisfactory results.     

Identification and Separation of Some Anions on Plain and Mixed Adsorbent Layers Using Water as Eluent

The analytical potential of water as an eluent in thin layer chromatographic separation of various anions on plain adsorbent layers (silica gel "G" alumina, and cellulose) as well as on beds containing different combinations of silica gel, alumina, or cellulose has been investigated. In addition to some important separation of anions, microgram separation of IO⁻₄ from milligram quantities of IO⁻₃, Bro⁻₃, MoO²⁻₄, and Fe (CN)³⁻₆ has been realized. The effect on pH of the sample in the separation of IO⁻₄ from accompanying ions has also been studied. The limits of detection and dilution limits of anions on alumina thin layers have been determined. NO⁻₂ in artificial seawater has been detected. The effect of CaCl₂, MgCl₂, and NaHCO₃ on some ternary separations of analytical importance has been examined.     

Adsorption of iodide ions on the Cd(0001) single crystal plane in methanol

The adsorption of I⁻ ions on the Cd(0001) single crystal plane from solutions in methanol has been investigated by impedance measurement method. The ionic charge due to the specific adsorption has been obtained using the mixed-electrolyte method for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of adsorption of ions has been calculated using the different modifications of the virial adsorption isotherm. It was found that under comparable conditions, the results obtained at constant electrode potential and at constant electrode charge are coincident and the adsorption of I⁻ anion increases in the sequence of solvents: water < methanol, ethanol, and metals: Cd < Bi. The electrosorption valency has been calculated. It was found that on the Cd(0001) plane the electrosorption valency of I⁻ anions has a constant value that is similar for methanol and ethanol and also for these solvents on Bi single crystal planes.     

Rapid flow injection method for the determination of sulfite in wine using the permanganate-luminol luminescence system

A simple, rapid and sensitive chemiluminescence method for the determination of sulfite has been developed by combining flow-injection analysis and its sensitizing effect on the known chemiluminescence emission produced by the oxidation of luminol in alkaline medium; in this work permanganate has been proposed as oxidizing reactive. The optimum conditions for the chemiluminescence emission were established. The chemiluminescence was proportional to the sulfite concentration over the range 1.6 × 10⁻⁵ and 4.0 × 10⁻⁴ mol L⁻¹. The detection limit was 4.7 × 10⁻⁶ mol L⁻¹ of sulfite. The method has been satisfactorily used for the determination of free and bound sulfite in wines.     

Oxygen production using La0.6Sr0.4Co0.2Fe0.8O3−α (LSCF) perovskite hollow fibre membrane modules

A phase-inversion/sintering technique has been employed in the production of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−α (LSCF) hollow fibre membranes, a bundle of which has then been placed in a high-temperature furnace for production of high purity oxygen from air at temperatures between 980 °C and 1060 °C. By applying a vacuum in the hollow fibre lumens, a product stream containing oxygen purity of 97.15% has been obtained. The downstream vacuum degree higher than 99 kPa shows negligible effect on the oxygen production rate. Studies on long-term operation suggest that the LSCF hollow fibre membranes are less stable for the oxygen production due to the segregation of the constituent membrane elements and the formation of new phases on the outer membrane surfaces. The effect of the operating cycle on the retrogression of membrane performance is much larger than that of duration used in a single cycle.     

Domestic gel sorbents for the purification of substances of plant origin

Summary 1. The degrees of swellability of the gels ÉD-1,5, ÉD-2,0, SDVp 1 · 10⁴ and SDVp 2 · 10³ and also of Sephadex G-15, in water and nine different organic solvents have been determined.2. The possibility has been shown of purifying technical tannin on Sephadex G-15 and the domestic gel ÉD-1,5 and of purifying technical hyoscyamine on the cation-exchange Sephadex SPC-25.3. On the basis of the results on swellability and on the purification of technical tannin, gel ÉD-1,5 has been shown to be equivalent to Sephadex G-15.Khar'kov Scientific-Research Institute of Pharmaceutical Chemistry. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 775–778, November–December, 1974.     

An ultrasensitive method for the determination of melamine using cadmium telluride quantum dots as fluorescence probes

An ultrasensitive and simple method for the determination of melamine was developed based on the fluorescence quenching of thioglycolic acid (TGA) capped CdTe quantum dots (QDs) at pH 11.0. In strong alkaline aqueous solution, the selectivity of the method has been greatly improved due to most heavy metal ions show no interference as they are in the precipitation form or in their anion form. Furthermore, CdTe quantum dots have higher quantum yields at higher pH. The method has a wider concentration range and lower detection limit. The influence factors on the determination of melamine were investigated and the optimum conditions were determined. Under optimum conditions, the fluorescence intensity change of TGA coated CdTe quantum dots was linearly proportional to melamine over a concentration range from 1.0 × 10⁻¹¹ to 1.0 × 10⁻⁵ mol L⁻¹ with a correlation coefficient of 0.9943 and a detection limit of 5 × 10⁻¹² mol L⁻¹. The mechanism of fluorescence quenching of the QDs has been proposed based on the infrared spectroscopy information and electrophoresis experiments in presence of melamine under alkaline condition. The proposed method was employed to detect trace melamine in milk powder and pet feeds with satisfactory results.     

An update on AOAC INTERNATIONAL new program activities

Significant progress has been made with the introduction of new AOAC INTERNATIONAL programs since plans were announced at BERM-5 in Aachen, Germany. The AOAC^® Technical Division on Reference Materials has been formed, the AOAC^® Peer-Verified Methods Program has been established and ready to accept methods for study, and the AOAC^® Test Kit Performance Testing Program has become operational.     

Electrical double layer and adsorption of iodide ions at the Bi | acetonitrile interface

The adsorption of I^? ions on the Bi(111) single crystal plane from solutions in acetonitrile has been investigated by impedance measurement method. The ionic charge due to the specific adsorption has been obtained using the mixed electrolyte method applied for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of ions adsorption has been calculated using the virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the Gibbs energy of I^? anion adsorption increases in the sequence of solvents: methanol < ethanol < propylene carbonate < acetonitrile. The electrosorption valency has been calculated and it was found that this parameter increases in the sequence propylene carbonate < ethanol < methanol < acetonitrile.     

Functionalization of polymeric membranes by impregnation and in situ cross-linking of a PDMS/β-cyclodextrin network

In this paper a new method for the functionalization of porous membranes with β-CD is reported. Porous polypropylene (PP) hollow fibres have been impregnated with a mixture composed by a partially cross-linked polydimethylsiloxane (PDMS) and β-cyclodextrin (β-CD). The prepolymerization of the PDMS components was necessary to avoid their inclusion in the β-CD cavity. The firm heterogenization of the β-CD was obtained by in situ cross-linking of the PDMS/β-CD network in the porous membranes. The presence of the PDMS/β-CD network in the membranes was confirmed by FT-IR-ATR (on the outer and inner surfaces) and EDX analyses (on the cross-section).The effect of the impregnation times on membrane morphology, loading and porosity has been investigated. The binding capacity of the heterogenized β-CDs has been tested using the phenolphthalein as guest molecule.     

Kinetic method for determination of nanogram amounts of copper(II) by its catalytic effect on hexacynoferrate(III)-citric acid indicator reaction

This paper describes a highly sensitive, selective catalytic-kinetic-spectrophotometric method for the determination of copper(II) concentration as low as 6 ng ml⁻¹. The method is based on the catalytic effect of copper(II) on the oxidation of citric acid by alkaline hexacyanoferrate(III). The reaction was followed by measuring the decrease in absorbance of hexacyanoferrate(III) at 420 nm (λ_max of [Fe(CN)₆]³⁻, ∈ = 1020 dm³ mol⁻¹ cm⁻¹). The dependence of rate of the indicator reaction on the reaction variables has been studied and discussed to propose a suitable mechanism to get a relation between the reaction rate and [Cu²⁺]. A fixed time procedure has been used to obtain a linear calibration curve between the initial rate and lower [Cu²⁺] or log[Cu²⁺] in the range 1 × 10⁻⁷ to 4 × 10⁻⁴ mol l⁻¹ (6.35-25,400 ng ml⁻¹). The detection limit has been calculated to be 4 ng ml⁻¹. The maximum average error is 3.5%. The effect of the presence of various cations, commonly associated with copper(II) and some anions has also been investigated and discussed. The proposed method is sensitive, accurate, rapid and inexpensive compared to other techniques available for determination of copper(II) in such a large range of concentration. The new method has been successfully applied for the determination of copper(II) in various samples.     

Thermal Methods Applied to the Glass Transition of Mixed Network AlPO4–BPO4–SiO2 Glasses

Glass transition effect of mixed network AlPO₄–BPO₄–SiO₂ glasses was studied. DTA/DSC and TMA measurements has been applied in the research. It has been found that glass transition effect has structurally sensitive properties. Glass transition temperature T _g, changes of specific heat (Δc _p)and thermal expansion coefficient (α) accompanying the process depend on the nature and the number of components forming the glassy framework. Character of chemical bonds combining them into the glass structure has an influence on the glass transition effect. Its course is dependent on the flexibility of the structure of glasses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Adsorption of low level51Cr(VI) from aqueous solution by bismuth trioxide: Kinetic and IR study

Radiotracer technique has been used for the investigation of adsorption of chromium (VI) traces on bismuth trioxide from aqueous solution. The effect of pH (2–10), concentration of chromate solution (10^–6–10^–2M) and temperature (303–323 K) has been thoroughly investigated. The influence of certain foreign ions has also been studied. The calculated kinetic and thermodynamic parameters indicate the first order rate law, spontaneity and exothermic nature of the adsorption process. Further, IR studies have established the chemical interaction between the sorbate and sorbent and a possible mechanism of the sorption process based on ligand exchange has been proposed.     

Choice of the best region for channel-by-channel summation of estimating the intensity of single photopeaks

The influence of partial peak width integration on the statistical error has been investigated. It has been shown that integration of the central photopeak part —±(0.55–0.64) FWHM for narrow peaks and ±(0.50–0.53) FWHM for wide peaks-allows to decrease the statistical error 1.5–2.0 times in comparision with the TPA method. The results obtained are valid both for real photopeaks and for smoothed spectra. The theoretical results have been confirmed by experimental data.     

π–π Stacking Interaction of Metal Phenoxyl Radical Complexes

π–π stacking interaction is well-known to be one of the weak interactions. Its importance in the stabilization of protein structures and functionalization has been reported for various systems. We have focused on a single copper oxidase, galactose oxidase, which has the π–π stacking interaction of the alkylthio-substituted phenoxyl radical with the indole ring of the proximal tryptophan residue and catalyzes primary alcohol oxidation to give the corresponding aldehyde. This stacking interaction has been considered to stabilize the alkylthio-phenoxyl radical, but further details of the interaction are still unclear. In this review, we discuss the effect of the π–π stacking interaction of the alkylthio-substituted phenoxyl radical with an indole ring.     

A disposable electrochemical sensor for the determination of indole-3-acetic acid based on poly(safranine T)-reduced graphene oxide nanocomposite

A disposable electrochemical sensor for the determination of indole-3-acetic acid (IAA) based on nanocomposites of reduced graphene oxide (rGO) and poly(safranine T) (PST) was reported. The sensor was prepared by coating a rGO film on a pre-anodized graphite electrode (AGE) through dipping-drying and electrodepositing a uniform PST layer on the rGO film. Scanning electron microscopic (SEM) and infrared spectroscopic (IR) characterizations indicated that PST-rGO formed a rough and crumpled composite film on AGE, which exhibited high sensitive response for the oxidation of IAA with 147-fold enhancement of the current signal compared with bare AGE. The voltammetric current has a good linear relationship with IAA concentration in the range 1.0 × 10⁻⁷-7.0 × 10⁻⁶ M, with a low detection limit of 5.0 × 10⁻⁸ M. This sensor has been applied to the determination of IAA in the extract samples of several plant leaves and the recoveries varied in the range of 97.71-103.43%.     

Effective length of the alkyl chain and thermal behaviors of Langmuir–Blodgett films of octadecylammonium laurate, octadecylammonium octadecanoate and octadecylammonium tetracosanoate

Thermal behaviors of 11-layer Langmuir–Blodgett (LB) films of the double long-chain compounds of octadecylammonium laurate (ODALA), octadecylammonium octadecanoate (ODASA) and octadecylammonium tetracosanoate (ODATA) have been investigated by Fourier transform infrared spectroscopy. The temperature-dependent infrared spectra show that thermal stability of the three kinds of LB films depends upon the length of the hydrocarbon chain. The LB film of ODALA undergoes an order–disorder transition in the temperature range of 50–65 °C. In contrast, the ODATA LB film has the phase transition temperature range of 80–90 °C. Of particular interest is that both ODASA and ODATA LB films have nearly the same phase transition temperature range of 80–90 °C, indicating that the replacement between tetracosanoic acid and stearic acid has little effect on the thermal stability of the two compounds. The above observations suggest that the effective length of the alkyl chains, which is determined by the component with a shorter chain in the double long-chain compounds, has a dominant influence on the thermal stability. It is very likely that the whole chain of the shorter chain component such as octadecylamine in ODATA has contribution to the thermal stability while only the effective length of the longer alkyl chain component gives a significant effect.