The development of a biosensor based on the immobilization of horseradish peroxidase (HRP) within a zirconium alkoxide-polyetilenimine film onto screen-printed electrodes (SPE) for acetaminophen detection and acetaminophen quantification in pharmaceutical products is described. The biosensor operation mode is based on monitoring the amperometric signal produced by the electrochemical reduction of the enzymatically generated electroactive oxidized species of acetaminophen in the presence of hydrogen peroxide. The enzyme immobilization is performed by retention in a polyethylenimine-zirconium alcoxide porous gel film, a technique that offers good entrapping and a protective environment for the biocomponent due to the hydration properties of the immobilization layer. SPEs have the advantage of being easily mass-produced at low costs with superior characteristics in comparison with classical electrode materials. In this configuration, zirconium alkoxide demonstrates its electrocatalytic activity. The biosensor allows the quantification of acetaminophen with a limit of detection of 6.21×10?8 M and a linear range between 4.35×10?7 M and 4.98×10?6 M. Finally, the biosensor is applied to the quantitative analysis of acetaminophen in Perdolan® tablets.
Specular reflection infrared microspectroscopy was used for chemical imaging of cross-sectioned urinary stones to determine their chemical composition and morphology simultaneously. Absorption spectral bands were recovered from reflection spectra by Kramers-Kronig transform. FUse of far-infrared radiation provides high-contrast images and allows more precise constituent distribution determinations than mid-infrared because band asymmetry after the transform caused by diffuse reflection is less in the far-infrared.
Magnetic fluid applications require stability under demanding conditions. Complete magnetic fluids and their component surfactants and dispersing oils were irradiated. Their subsequent thermal oxidation was characterized by chemiluminescence and DSC. Except for polyisobutylsuccinic anhydride, irradiation sensitized the components toward oxidation. The components were ranked by stability. Complete fluids were more stable than would be predicted from their components suggesting that they may be used for nuclear applications.
An one-pot approach was developed for the synthesis of substituted 5,7-dihydro-1,6-naphthyridines and 5,6,7,8-tetrahydroquinolines with moderate to good yields. This pathway is a modified two-step synthesis of Kröhnke pyridine and involves a four-component tandem reaction of N-phenacylpyridinium bromide, aromatic aldehydes, substituted or nitrogen-containing cyclic ketones and a nitrogen source. This multi-component reaction is performed using microwave irradiation heating of the reaction substrates under an environment of NH4OAc/HOAc.
New vapor-liquid equilibria (VLE) data at 323.15, 333.15, 343.15, and 353.15 K and pressures up to 112.9 bar are reported for the carbon dioxide + 2-methyl-2-propanol system. The experimental method used in this work was a static analytical method with liquid and vapor phases sampling using a rapid online sampler injector (ROLSI?) coupled to a gas chromatograph (GC) for analysis. Measured VLE data and literature data for carbon dioxide + 2-methyl-2-propanol system were modeled with the Soave-Redlich-Kwong (SRK) cubic equation of state with classical van der Waals (two-parameter conventional mixing rule, 2PCMR) mixing rules. A single set of interaction parameters that lead to a correct phase behavior was used in this work to model the new VLE data and critical points of the mixtures in a wide range of temperature and pressure. The SRK prediction results were compared to the new data measured in this study and to available literature data.
After oxidation of tannins (Tannins 1–3) extracted from grape seeds, Tanoxil compounds with increased solubility and enhanced antioxidant activities were synthesized. In this research, ABTS+· assay and a chemiluminescence method were used for antioxidant measurement of hydrophilic compounds (Tanoxils 1–3).
It was observed that the antioxidant activity (AA, %) is very similar for the three samples, while at the same time AA is quite high (93.16%–96.48%). The percentage of inhibition by ABTS+· is higher for Tanoxil 2 (96.4%) as compared to Tannin 2 compound (14.34%). Moreover, the total content (TCF) of carboxyl and phenolic groups was investigated. TCF values, determined for Tanoxil products, revealed a double (Tanoxil 1) or triple (Tanoxil 2) increase as compared to the value of the TCF of Tannin 1. Tanoxil products represent an interest for future research as they have a high AA (96.4%) and the content of acidic groups is significant (TCF, 0.191 meq g?1).
The phase behavior of the carbon dioxide + cycloalkane mixtures usually receives low attention, though these systems are important for many industries, e.g. the carbon capture and storage. In this paper calculations results for the carbon dioxide + cyclopentane binary system are presented, based on SRK and PR cubic equations of state with classical van der Waals mixing rules. A single set of binary parameters for each model was proposed to predict the global phase behavior of the system in a wide range of pressure and temperature. Albeit the thermodynamic models used are simple, they are able to represent fairly well the phase behavior of the system analyzed in this paper.
Biocatalysts with microorganisms immobilized on solid carriers could provide the solution for development of continuous industrial processes for ethanol obtaining by fermentation of sugars. In this study, modified polyacrylamide hydrogels and marrow stem sunflower are used as supports for Saccharomyces cerevisiae yeast immobilization. The obtained structures are used for fermentation of molasses in batch systems. The free yeast cells are used as reference. The modification of polyacrilamide matrix with (2-hydroxyethyl)methacrylate has a positive effect on structure pore uniformity and fermentation performance. The mechanical properties of the obtained biocatalysts are compared. The novel natural matrix has net superior compression strength.
The single crystal X-ray structures and the spectroscopic properties of complexes of monensic acid (C36H62O11·H2O) with toxic metal ions of Cd(II) and Hg(II) are discussed. The cadmium(II) complex (1) is of composition [Cd(C36H61O11)2(H2O)2] and crystallizes in the monoclinic system (space group P2(1), Z = 2) with a = 12.4090(8), b = 24.7688(16), c = 14.4358(11) Å, β = 91.979(7)°. Two ligand monoanions are bound in a bidentate coordination mode to Cd(II) via the carboxylate and the primary hydroxyl oxygens occupying the equatorial plane of the complex. The axial positions of the inner coordination sphere of Cd(II) are filled by two water molecules additionally engaged in intramolecular hydrogen bonds. The Hg(II) complex (2), [Hg(C36H60O11)(H2O)], crystallizes in the orthorhombic system (space group P2(1)2(1)2(1), Z = 4) with a = 12.7316(2), b = 16.4379(3), c = 18.7184(4) Å. The monensic acid reacts with Hg(II) in a tetradentate coordination manner via both oxygen atoms of the carboxylate function and oxygens of two hydroxyl groups. The twofold negative charge of the ligand is achieved by deprotonation of carboxylic and secondary hydroxyl groups located at the opposite ends of the molecule. Hg(II) is surrounded by five oxygen atoms in a distorted square pyramidal molecular geometry.
Changes of total content of phenolic substances, alteration in total titratable acidity and differences in tartaric acid content in grapes of four white (Müller-Thurgau — MT, Pinot Blanc — Rulandské bílé in Czech, RB, Sauvignon (Sg), and Muscat Ottonel — Mu?kát Ottonel in Czech, MO) and two blue (Dornfelder — Df and Blue Frankish — Frankovka in Czech, Fr) grapevine varieties throughout their growth, ripening and maturing (July–November). Potentiometric titration was applied for the determination of total titratable acids in grapes (expressed as tartaric acid equivalents in g L?1). A spectrophotometric method according Rebelein based on the formation of a colored complex of ammonium metavanadate and tartaric acid was used for determination of tartaric acid in green juice made by pressing unripe grapes. A spectrophotometric method based on reduction of phosphomolybdato-tungsten complex in alkaline solution using Folin-Ciocalteau reagent was applied for determination of total content of phenolic substances (TCP).
Common waste glasses (window, bottle glass or tableware) with fly ash form a glass matrix for chromium waste immobilization. Soluble chromium from residual waters was adsorbed on fly ash; the resulting solid contained 23.7% Cr6+. The three glass wastes, chromium-containing fly ash, and borax were used to make glasses in weight ratios waste glass: borax: fly ash of 1: 1: 1 and 1.5: 0.5: 1. The hydrolytic stability ranged from 18.46 to 28.13 µg g?1 soluble Na2O, qualifying them in the HGB1 class. The chemical stability, characterized by the dissolution rate, was 0.011–0.077 µg cm?2 h?1, depending on the glass composition and the aggressive medium pH. The chromium leachability is influnced by the glass composition and the pH of the leaching solution, ranging between 0–0.015% of the total chromium. Chromium waste vitrification is a viabile solution with multiple economic advantages.
In this study, microwave assisted a hydrodistillation process (MWHD) of essential oils from lavender (Lavandula angustifolia Miller) was investigated. In order to examine any potential differences in essential oil extraction, the lavender flowers underwent enzymatic pretreatment.A 23 factorial design of experiments, combined with statistical methods of data analysis were used to optimize enzymatic pretreatment and to evaluate the influence of major variables (enzyme concentration, temperature and pH) on the performance of the microwave assisted extraction.Under optimal conditions, an extraction yield of 24 mg oil g?1 substrate was achieved (an increase by approximately 25% in comparison with the classic extraction conditions of conventional hydrodistillation).The main compounds of the essential oils obtained were analyzed and identified by gas chromatography coupled to mass spectrometry (GC-MS). Analyzing the data obtained indicated that the content of main compounds (linalool and linalyl acetate ? 73%) was greater than that obtained by conventional extraction (67%).
Electron beam (EB) irradiation is a useful method to generate stable silver nanoparticles without the interference of inherent impurities generated from chemical reactions. Our experiments were carried out using linear electron beam accelerators with two different EB absorbed dose rates: 2 kGy min?1 and 7–8 kGy s?1, and with different absorbed dose levels. The optimum conditions for silver nanoparticles (AgNPs) generation by radiolysis, or by radiolysis combined with chemical reduction, were established. In order to obtain a good yield for AgNPs synthesized by radiolysis, a high dose rate is required, resulting in a rapid production process. At low absorbed dose rates, the utilization of a stabilization agent is advisable. By modifying the experimental conditions, the ratio between the chemical and radiolytic reduction process can be adjusted, thus it is possible to obtain nanoparticles with tailored characteristics, depending on the desired application.
We successfully synthesized tin dioxide nanoparticles with polyhedral morphology via an ethylene glycol assisted sol-gel approach. The structural characteristics of three tin dioxide samples were investigated after being thermally treated at 400°C, 600°C and 800°C. X-ray diffraction (XRD) patterns clearly show the formation of single phase tin dioxide nanoparticles, with crystallite size of 6–20 nm, in good correlation with Fourier transform infrared (FTIR) spectra. Transmission electron microscopy (TEM) analysis confirms the formation of 6nm polyhedral nanoparticles for the 400°C sample. Ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectra suggest a high concentration of oxygen vacancies. The oxygen vacancy concentration increases with temperature, due to the combined action of the formation of VO and the energetic O compensation. X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of single phase tin dioxide and the presence of oxygen vacancies in good agreement with UV-VIS and PL data.
Chemical analysis of various biological matrices is routinely used for assessment of human exposure to various toxic metals. In this work, 489 samples of urinary calculi originating from almost the whole of The Czech Republic, were collected and subjected to mineralogical and elemental analysis. This study was aimed at mercury, the content of which was determined using thermo-oxidation — cold vapor — atomic absorption spectrometry. The effects of mineralogical composition, sex, age and region were recorded in order to verify the applicability of urinary calculi for biomonitoring. Relationships with other minor and trace elements were also investigated. Association of mercury with whewellite mineral was observed as well as a remarkable relationship with selenium, confirming the role of selenium in mercury excretion. No statistically significant effect was observed on the mercury content in stones with regard to the sex or region. Median values in age groups follow a trend with the maximum median value 0.365 mg kg?1 in the group of 41–50 year old donors, decreasing to 0.060 mg kg?1 for the oldest group (81–92 years). Our results confirm that urinary calculi can be helpful in providing complementary information on human exposure to mercury and its excretion.
Direct immersion solid-phase microextraction has been optimized and applied to the simultaneous determination of the neutral and basic pharmaceuticals: caffeine, carbamazepine, clomipramine, chlorprothixene and clotrimazole at low concentrations in municipal wastewater. Two absorption type stationary phases: polydimethylsiloxane (PDMS) and polyacrylate (PA) have been found to be most effective for extraction of target analytes. The separation and detection were carried out by gas chromatograph coupled with mass spectrometer working in the selected ion monitoring mode. The method was validated for linearity, detection and quantitation limits, selectivity and precision. The average correlation coefficient of the calibration curves was 0.9933. The LOD values in influent and effluent wastewater were in the range of 10–145 ng L?1 and 4–111 ng L?1, respectively, which were a bit higher than those in the deionized water due to matrix effect. The high values of distribution coefficient (Kfs) in PDMS/water and PA/water systems (log Kfs between 3.05 and 4.23) indicates the very high applicability of these stationary phases for determination of carbamazepine, clomipramine, chlorprothixene and clotrimazole in water samples.
Hydrogen titanate nanotubes (H-TTNT) were synthesized by the alkali hydrothermal method followed by proton exchange and then submitted either to thermal treatment or to acid hydrothermal reaction to generate TiO2-anatase nanocrystals of different morphologies. The samples were characterized by XRPD, TGA, sulfur analysis, N2 physisorption, UV-Vis spectroscopy and TEM. Their photocatalytic activities were determined by measuring the NO conversion in inert gas stream passed through the powder catalyst bed under UV radiation. Incomplete transformation into anatase resulted in nanomaterials with low activity due to coexistence with H-TTNT or TiO2-B precursors. Anatase specimens derived from H-TTNT aged in strong sulfuric acid media contained equidimensional nanoparticles, but retention of sulfate negatively affected their photocatalytic activity. Combining milder acidic pH with higher aging temperature, allowed synthesis of a sulfate free anatase with the same optical properties and specific surface area as the counterpart produced by calcination of H-TTNT at 550°C; however, the former exhibited truncated bi-pyramid nanocrystals and the other adopted the form of nanorods. This latter showed the highest photocatalytic activity for NO abatement, outperforming the benchmark photocatatyst TiO2-P25; this improved activity was tentatively ascribed to the maximization of high energy {001} facets in anatase nanorods formed during calcination of H-TTNT.
In the present study, we propose a method for the evaluation of different classes of xenobiotic organic compounds enclosed in the municipal landfill leachate using comprehensive two-dimensional gas chromatography coupled with quadrupole mass spectrometry (GCxGC-qMS). Here we show that, due to high peak capacity of comprehensive two-dimensional gas chromatography, in a single run it is possible to separate compounds with different physical-chemical properties (such as aliphatic and aromatic compounds, polyaromatic hydrocarbons, phenols, phthalates, aldehydes, ketones, nitrogen containing compounds, organo-phosphoric flame retardants etc.), compounds which have proved to be endocrine disruptors, compounds that are persistent, bioaccumulative and toxic, carcinogenic, mutagenic, teratogenic, reprotoxic or harmful for the environment. Even though a solvent extraction method has been optimised, the extraction step still remains the main problem for a comprehensive characterization of all classes of organic toxicants enclosed in the municipal landfill leachate.
Bacterial cellulose (BC), a natural polymer with unique physical and mechanical properties, has several applications in the biomedical field, including drug loading and controlled drug delivery. For this study, a Box-Behnken experimental design was employed as a statistical tool to optimize the release of a model drug, amoxicillin, from BC membranes. Independent variables studied were the concentration of the drug (X1), the concentration of glycerol (X2) and the concentration of a permeation enhancer (X3). From the variables studied, drug concentration had the highest effect on drug release. Among the other independent variables, th linear and quadratic X2 terms, the linear X3 term and the interaction term X2X3 were found to affect the release of amoxicillin from bacterial cellulose membranes.
