Characterization of CaTi0.9Fe0.1O3/La0.98Mg0.02NbO4 composite

A composite of CaTi_0.9Fe_0.1O₃ and electrolyte material, i.e. magnesium doped La_0.98Mg_0.02NbO₄ was prepared and studied. The phase content and the sample microstructure was examined by an X-ray diffraction method and scanning electron microscopy. EDS measurements were done both for composite samples and the diffusion couple. The electrical properties were studied by four terminal DC method. The high-temperature interaction between the two components of the composite has been observed. It has been suggested that lanthanum diffused into the perovskite phase and substituted for calcium whereas calcium and niobium formed the Ca₂Nb₂O₇ pyrochlore phase. At 1500°C very large crystallites of the pyrochlore were observed. Regardless of strong interaction between the composite components, its total conductivity was weakly dependent on the sintering temperature.     

A novel approach to the rapid determination of amoxicillin in human plasma by solid phase microextraction and liquid chromatography

A new approach to the rapid determination of amoxicillin (AMO) in human plasma followed by solid phase microextraction (SPME) fiber coatings based on conducting polymers (polypyrrole and polythiophene) and high performance liquid chromatography (HPLC) has been described. The porous structures of the electrochemically deposited polymer coatings have been characterized by scanning electron microscopy (SEM). The experimental parameters relating to the extraction efficiency of the SPME fibers such as pH, extraction time and desorption conditions (solvents, time) were studied and selected. The SPME/HPLC-UV method was linear over a working range of 1-50 μg ml(-1). The inter-day accuracy (expressed as coefficients of variations, CVs) was less than 15% and precision (expressed as the relative standard deviations, RSDs) with percentage values was less than 5.9%. Amoxicillin was found to be stable in the human plasma at room temperature (20 °C) within 8 hours. The developed method was successfully applied to the analysis of real human plasma samples. The limit of detection and limit of quantification for amoxicillin in plasma were 1.21 μg ml(-1) and 3.48 μg ml(-1), respectively.     

Determination of volatile and non-volatile products of milk fermentation processes using capillary zone electrophoresis and solid phase microextraction coupled to gas chromatography

The aim of the investigations was to develop analytical methods for the determination of selected volatile and non-volatile organic compounds numbering among the final products of milk fermentation. The analyzed compounds were as follows: biacetyl and carboxylic acids (formic, acetic, citric, and lactic). The model yogurt was prepared under controlled conditions in our laboratory by addition of the selected bacteria (Lactobacillus bulgaricus and Streptococcus thermophilus) to the milk sample. The temperature, time, and stirring were controlled during the fermentation process. Factors considered in SPMPE-GC-FID method development included fiber exposure time, salt addition, temperature of extraction, and temperature of desorption. Various SPME fibers, for example with PDMS, CAR/PDMS, PA, and PDMS/DVB coatings, were tested to obtain the highest recovery of the investigated compounds extracted from yogurt samples. Based on these preliminary experiments, qualitative and quantitative analyses for the determination of biacetyl were performed by SPME-GC-FID. Moreover, a capillary zone electrophoresis method was developed for the determination of carboxylic acids in the yogurt samples. The buffer composition as well as deproteinization by acetonitrile were found to have a crucial effect on the analysis.     

Antimicrobial properties of biosynthesized silver nanoparticles studied by flow cytometry and related techniques

This work reports the effect of silver bionanoparticles (Bio(AgNPs) synthesized by Actinobacteria CGG 11n on selected Gram (+) and Gram (–) bacteria. Flow cytometry, classical antibiogram method and fluorescent microscopy approach was used for evaluation of antimicrobial activity of Bio(AgNPs) and their combination with antibiotics. Furthermore, the performed research specified the capacity of flow cytometry method as an alternative to the standard ones and as a complementary method to electromigration techniques. The study showed antibacterial activity of both BioAgNPs and the combination of antibiotics/BioAgNPs against all the tested bacteria strains in comparison with a diffusion, dilution and bioautographic methods. The synergistic effect of antibiotics/BioAgNPs combination (e.g. kanamycin, ampicillin, neomycin and streptomycin) was found to be more notable against Pseudomonas aeruginosa representing a prototype of multi‐drug resistant “superbugs” for which effective therapeutic options are very limited.     

Effect of chemically bonded stationary phases and mobile phase composition on beta-blockers retention in RP-HPLC

The effects of stationary and mobile phase on retention of 18 beta-adrenolytic drugs (beta-blockers) have been studied. Four 'deactivated surface' stationary phases (polar-embedded or end-capped) were examined. Special attention was drawn to the cholesterolic (SG-CHOL) and alkylamide (SG-AP) stationary phases, and their application for analysis of the compounds. The retention of analyzed substances was also examined in terms of mobile phase composition. Sixteen different configurations of mobile phases were prepared, all based on methanol and acetonitrile with ammonium acetate and ammonium formate. The difference in retention between ammonium formate and acetate water solutions, and peak shape changes related to the addition of triethylamine (TEA), were investigated. Principal component analysis was used to find the similarities between stationary phases. Polar-embedded phases synthesized on the same sorbent possess very similar properties. All phases based on silica gel compared with the monolithic column also showed similarities in retention of beta-blockers. The addition of TEA to the mobile phase did not influence strongly the retention, and analysis of asymmetry factors showed only a little peak broadening for a few compounds on the monolithic column.     

Application of TLC and OPLC in the Determination of Pigments from Natural Products

JPC – Journal of Planar Chromatography – Modern TLC - Planar chromatographic methods thin-layer chromatography (TLC) and over-pressure thin-layer chromatography (OPLC) have been...     

Fe-N-C catalysts for oxygen electroreduction under external magnetic fields:Reduction of magnetic O2 to nonmagnetic H2O

An extensive analysis of iron-nitrogen-carbon(Fe-N-C)electrocatalysts synthesis and activity is presented concerning synthesis conditions such as initial Fe content,pyrolysis temperature and atmosphere(inert N₂,reducing NH₃,oxidizing Cl₂ and their sequential combinations)and the influence of an external magnetic field on their performance in oxygen reduction reaction(ORR).Thermosetting porous polymers doped with FeCl₃ were utilized as the Fe-N-C catalysts precursors.The pyrolysis temperature was varied within a 700-900℃range.The temperature and atmosphere of pyrolysis strongly affect the porosity and compositi on of the resultant Fe-N-C catalysts,while the in itial amount of Fe precursor shows much weaker impact.Pyrolysis under NH₃ yields materials similar to those pyrolyzed under an inert atmosphere(N₂).In contrast,pyrolysis under Cl₂ yields carbon of peculiar character with highly disordered structure and extensive microporosity.The application of a static external magnetic field strongly enhances the ORR process(herein studied in an alkaline environment)and the enhancement correlates with the Fe content in the Fe-N-C catalysts.The Fe-N-C materials containing ferromagnetic iron phase embedded in N-doped microporous carbon constitute attractive catalysts for magnetic field-aided anion exchange membrane fuel cell technology.     

Preparation and characterization of microporous fibers for sample preparation and LC‐MS determination of drugs

The aim of this study was the preparation of polypyrrole (PPy) fibers for solid phase microextraction (SPME). PPy coatings were obtained during the electrochemical polymerization process. The utility of various metal wires (Fe, Cu, Ag, Cu/Ag, kanthal and medical stainless steel) as a support for polymers was compared. Various experimental conditions of the synthesis process such as scan rate, voltage limits and number of scans and deposition time were applied. The average polymer thickness was in the range of 7–125 μm and its weight was in the scope of 0.65–5.6 mg. Different techniques, mainly elemental analysis, Fourier transform infrared spectroscopy, microscopy, and chromatography were performed for the characterization of obtained fibers with microporous structure. The extraction efficiency of cardiovascular drugs (metoprolol, propranolol, oxprenolol, propafenone and mexiletine) by means of fibers was tested. The concentration of mentioned compounds in standard solution was in the span of 10–150 ng/mL. LC‐MS was employed for determination of drugs in desorption solution. LODs varied from 0.013 to 1.51 ng/mL for metoprolol and mexiletine respectively. The repeatability of extraction was obtained with the RSD values lower than 10%.