Formation of oxide phases in the system Fe2O3−Gd2O3

The formation of oxide phases in the system (1 -<i>x</i>) Fe<sub>2</sub>O<sub>3</sub> +<i>x</i>Gd<sub>2</sub>O<sub>3</sub> was investigated for 0 <img src="/content/rp45r38lt0640713/xxlarge10877.gif" alt="les" align="MIDDLE" BORDER="0"><i>x</i> <img src="/content/rp45r38lt0640713/xxlarge10877.gif" alt="les" align="MIDDLE" BORDER="0"> 1. On the basis of XRD measurements the distribution of oxide phases, <img src="/content/rp45r38lt0640713/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-Fe<sub>2</sub>O<sub>3</sub>, Gd<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub>, GdFeO<sub>3</sub> and Gd<sub>2</sub>O<sub>3</sub> was determined, as a function of<i>x</i>. No solid solutions were observed with certainty even at the very ends of the concentration range. This was also confirmed by<sup>57</sup>Fe Mössbauer spectroscopy. New accurate crystallographic data for Gd<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub> are given. The formation of oxide phases in the system Fe<sub>2</sub>O<sub>3</sub>- Gd<sub>2</sub>O<sub>3</sub> is compared with the data for analogous system Fe<sub>2</sub>O<sub>3</sub>-Eu<sub>2</sub>O<sub>3</sub>.     

Implementation of diffractive optical element in four-wave mixing scheme for ex situ characterization of hydride vapor phase epitaxy-grown GaN layers

A holographic beam splitter has been integrated into a picosecond four-wave mixing (FWM) scheme. This modification significantly simplified the procedure of dynamic grating recording, thus making the FWM technique an easy-to-use tool for the holographic characterization of wide band gap materials. The novel FWM scheme was applied for characterization of hydride vapor phase epitaxy-grown undoped GaN layers of different thickness. It allowed the determination of carrier lifetime, diffusion coefficient, and carrier diffusion length by optical means, as well as the study of carrier recombination peculiarities with respect to dislocation and excess carrier density.     

A user-friendly PC-based data acquisition and analysis system for respirometric investigations

We have developed an easy-to-use computer-based system for recording, displaying, storing and analyzing signals generated by Clark-type oxygen electrodes. A user-friendly interface of Windows-based program BioMed significantly increases the productivity of investigations. It allows to process, control, present and archive the experimental data in real time. A 12-bit analog-to-digital-converter, analog and digital filters, a possibility to zoom the obtained respiratory curves and calculation of the respiration rates by a linear regression method increase the resolution of the estimated oxygen consumption rates. The new system enables to register even small changes, such as 3-5 ngatoms O/min, in respiration rates of biological objects -- enzymes, mitochondria and permeabilized muscle fibers. The system has been developed and is regularly used for the respirometric investigations at the Laboratory of Biochemistry, Institute for Biomedical Research, Kaunas University of Medicine.     

Separation of selective organic acids from wastewater through a polyol supported liquid membrane

Pesticide toxicity databases usually include data on pure chemicals (active ingredients). Technical pesticides formulations, however, are mixtures with adjuvants as applied to fields/crops. Two formulations of the same pesticide can differ in their environmental fate and their toxicity. This work presents the evaluation of the toxicity of the dinitroaniline herbicide, pendimethalin by simultaneous analysis of its respiration rate and generation of a membrane potential (Δ Ψ) in rat liver mitochondria. Chromatography grade pendimethalin (8.2·10<sup>?5</sup> ‐ 5.47·10<sup>?4</sup> M or 23 – 154 ppm) caused lower enhancement of the mitochondrial respiration and decrease of the Δ Ψ than technical grade pendimethalin (Stomp), i.e. the mixture of pure ingredient and adjuvant(s). These effects are comparable to those of 2,4‐dinitrophenol. Pure and technical grade pendimethalin acts as an uncoupler of oxidative phosphorylation in mitochondria (enhances respiration and diminishes Δ Ψ). These data conflict with the statement, presented in the US EPA manual <i>Recognition and Management of Pesticides Poisonings</i>, that pendimethalin does not act as an uncoupler of oxidative phosphorylation.     

Recovery of EDTA from complex solution using Cu(II) as precipitant and Cu(II) subsequent removal by electrolysis

Ethylendiaminetetraacetate (EDTA) is a chelating agent widely used in industry and agriculture. Resistant to chemical and biological degradation EDTA represents a serious ecological problem. In order to avoid the outlet into the environment a new method of EDTA recycling has been proposed. The method involves substituting of the metal ions in EDTA complexes by Cu(II) and formation of an insoluble Cu2EDTA.4H2O compound at the excess of Cu(II) ions in weakly acidic solutions. Cu(II) ions substitute such metal ions as Ni(II), Zn(II), Co(II), Cd(II), Ca(II) and Mg(II). After treatment of the precipitate with water only, acidic or alkaline solutions the copper from the suspension formed can be removed by electrolysis. The highest current efficiency under galvanostatic conditions is in alkaline solutions, however, the highest yield of EDTA recovery is in acidic solutions. FT-IR investigations and chemical analysis of the precipitate formed have shown that in acidic and in alkaline solutions, H4EDTA and Na2H2EDTA.2H2O were formed, respectively. Electrolysis in acidic solutions gives the best results, i.e. the formed H4EDTA contains the highest amount of EDTA (95%) and the lowest amount of copper (0.01%).     

Single-run capillary electrophoretic determination of inorganic nitrogen species in rainwater

A capillary electrophoretic (CE) method for the simultaneous determination of nitrate, nitrite, and ammonium ions has been developed. Direct (NO3-, NO2-) and indirect (NH4+) UV detection at 214 nm in conjunction with electromigration sampling from both ends of the capillary was used. The optimized separations were carried out in 10 mmol/L imidazole sulfate, 2 mmol/L 18-crown-6, and 0.02 mmol/L tetradecyltrimethylammonium hydroxide electrolyte (pH 4.0). The method permits excellent separation of three nitrogen species in only 4 min. A 1 x 10(-4) mol/L KBr solution was used as an internal standard to limit possible electrokinetic injection biases. Experimental results showed that the use of an anionic internal standard for cationic analytes and vice versa gives only slightly better precision than analysis with no internal standard. Using Br- internal standard for NO3- and NO2- ions and K+ for NH4+, peak area RSD values decrease significantly. The proposed system was applied to the speciation of inorganic nitrogen ions in rainwater samples. The recovery tests established for external calibration and standard addition techniques using one or two internal standards were within the range 100 +/- 10%. The CE results agree with those obtained by spectrophotometric methods.     

Intermittent contact AFM using the higher modes of weak cantilever

Employing the higher vibration modes of weak cantilevers enables operating frequencies up to megahertz to be reached, at the same time keeping the force on the sample reasonably low. This allows the interaction time between the tip and the surface to be reduced and should cause the response of surface to be dominated by surface stiffness. The simple distributed mass cantilever model is presented which shows that higher eigenmodes exhibit better sensitivity to surface properties. The images of laser-treated polymer on glass show the ability of the method to distinguish between the material phases with different properties.     

Electrochemical method for the detection of lipase activity

A novel electrochemical technique for the general assay of lipase activity is described. The method utilizes a solid-supported lipase substrate, which is formed by dripping and drying a small amount of an ethanol solution of 9-(5'-ferrocenylpentanoyloxy)nonyl disulfide (FPONDS) onto gold modified by a hexanethiol self-assembled monolayer. The redox ferrocene group of FPONDS generates the electrochemical signal, the intensity of which is proportional to the number of FPONDS molecules at the interface. Electrochemical and surface-enhanced infrared absorption spectroscopic data, as well as control experiments with an engineered, deactivated mutant enzyme, demonstrate that the wild-type lipase from Thermomyces lanuginosus is capable of cleaving the ester bonds of FPONDS molecules via an enzymatic hydrolysis mechanism, which includes the adsorption of the lipase onto the substrate surface. The hydrolysis liberates the ferrocene groups from the interface triggering a decay of the electrochemical redox signal. The rate of the electrochemical signal decrease is proportional to the lipase activity/concentration. These data suggest a general method for the direct measure of enzymatic activity of lipases.