Spectroscopic characterization of the stabilising activity of migrating HALS in a pigmented PP/EPR blend

In previous work, the FT-IR maximum of absorption of a low molecular weight HALS containing a sebacate structure was reported to shift from 1738 to 1732 cm⁻¹ during the photo-aging of polypropylene. Previous studies have shown that the reduced mobility of the molecule caused the absorption to shift towards lower frequencies while decreasing its stabilizing activity. This paper presents further results evidencing the loss of activity of the low molecular weight HALS and proposes a novel mechanistic interpretation for the observed spectral shift.     

A spectrophotometric method for determination of the solubilizing activity of cellulase complexes

Summary A standardized spectrophotometric method for determination of the solubilizing activity of microbial cellulase complexes has been developed. It is based on the release of coloured compounds from microcrystalline cellulose (Avicel SF^®) dyed with Levafixbrillantrot E-2B^®.

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Eine spektrophotometrische Methode zur Bestimmung der solubilisierenden Aktivität des Cellulase-Komplexes (Kurze Mitteilung)

Zusammenfassung Es wurde eine standardisierte spektrophotometrische Methode zur Bestimmung der Aktivität des Cellulase-Komplexes von Mikroorganismen ausgearbeitet. Die Methode beruht auf der Möglichkeit, mit Levafixbrillantrot E-2 B^® gefärbte mikrokristalline Cellulose (Avicel SF^®) als Substrat zu verwenden.

     

A comparison study between a disposable electrochemical DNA biosensor and a Vibrio fischeri-based luminescent sensor for the detection of toxicants in water samples

In the present study, a comparison between a disposable electrochemical DNA biosensor and a Vibrio fischeri-based luminescent sensor for the detection of toxicants in water samples was made.In order to realize this study, a disposable electrochemical DNA biosensor has been reported. The DNA biosensor is assembled by immobilizing double stranded Calf Thymus DNA onto the surface of a disposable carbon screen-printed electrode. The oxidation signal of the guanine base, obtained by a square wave voltammetric scan, is used as analytical signal to detect the DNA damage; the presence of low molecular weight compounds with affinity for nucleic acids is measured by their effect on the guanine oxidation peak.Wastewater samples provided during First European Interlaboratory Exercise on water toxicity in the course of the project SWIFT-WFD were analyzed, and biosensor results were compared with a currently used toxicity test ToxAlert^®100 based on the bioluminescence inhibition of Vibrio fischeri. This test have been used because is rapid, easy handling and cost effectively responses for the toxicity assessment in real water samples.The results showed a promising correlation between two tests used for the detection of toxic compounds in water samples.     

Evaluation and optimization of solid adsorbents for the sampling of gaseous methylated mercury species

This study evaluates the suitability of commercially available adsorbents for the measurement of gaseous organic mercury species namely monomethylmercury (MMHg) and dimethylmercury (DMHg).     

Thermodynamic approach for studying both the retention and complexation mechanisms with hydroxy-propyl-beta-cyclodextrin of a phenoxy-propionic acid herbicide series

The retention and complexation mechanisms of a herbicide series were studied from a chromatographic approach using a novel column called “Nautilus^®”. The effects of water fraction and the hydroxy-propyl-β-cyclodextrin (HP-β-CD) concentration in the mobile phase were analysed in relation to the column temperature. Two retention models of phenoxy-propionic acid (PPA) derivatives were investigated. It was shown that the retention mechanism was led by free PPA herbicide for low HP-β-CD concentrations and by the PPA/HP-β-CD complex for the highest ones. In addition, an enthalpy-entropy compensation study revealed that both the solute retention and complexation mechanisms were independent of the number of chlorine atoms in the structure. Also the thermodynamic results showed that (1) the retention process depended on the water fraction (X) in the mobile phase and (2) the PPA/HP-β-CD complexation mechanism was shown to be entropically controlled.     

Voltammetric assay of rifampicin and isoniazid drugs, separately and combined in bulk, pharmaceutical formulations and human serum at a carbon paste electrode

The electrochemical oxidation of both the rifampicin (RIF) and isoniazid (INH) drugs has been investigated by cyclic and square-wave voltammetry in Britton-Robinson buffers (pH 2-11) at a carbon paste electrode. The oxidation of rifampicin generated a well-defined pH-dependent quasi-reversible anodic-cathodic peak couple corresponding to a mechanism involving the transfer of two electrons/two protons, typical to that of hydroquinones, in addition to an irreversible anodic peak at a more positive potential which may be due to the oxidation of phenolic hydroxyl group. For the isoniazid, an irreversible anodic peak was observed, which may be attributed to the irreversible oxidation of the amide moiety of the drug molecule. A validated square-wave adsorptive anodic stripping voltammetric procedure was described to assay the two drugs separately or combined in pharmaceutical formulations and human serum. The recoveries of RIF in rimactane^® capsules (300 mg RIF) and INH in isocid^® tablets (200 mg INH) were found to be 98.57±0.81% and 100.57±0.74%, respectively. The proposed procedure was also successfully applied to simultaneous assay of rifampicin and isoniazid drugs combined in rimactazid tablets (150 mg INH+300 mg RIF) with recoveries of 98.79±0.97% and 99.54±0.74%, respectively, without the necessity for sample pretreatment or time-consuming extraction steps prior to the analysis. The results were favorably compared to those obtained by the reported USP method. Moreover, the proposed procedure was successfully applied to simultaneous assay of both drugs in human serum samples with limits of detection and quantitation of 5×10⁻⁸ and 1.7×10⁻⁷ M for RIF and 6.1×10⁻⁸ and 2×10⁻⁷ M for INH.     

Evaluation of two aquatic passive sampling configurations for their suitability in the analysis of estrogens in water

The presence of estrogens in the aquatic environment has been the target of several studies in the last decade. Newly developed passive sampling techniques for polar organic chemicals show great promise for the assessment of long-time exposure of aquatic organisms to emerging contaminants. In the present work, two configurations of the Chemcatcher^® passive sampler have been tested for their applicability to the analysis of seven estrogens in water. Accumulation experiments in the laboratory, to calculate the uptake rates, and a field trial show that the polar configuration of this device may be used for the efficient sampling and determination of estrogens in water. Time weighted average concentrations were determined in the field trial and compared with spot sampling concentrations. The detection of estriol using passive sampling, although not found with spot sampling, clearly demonstrates the value of this technique in assessing relevant concentrations of estrogens in the aquatic media.     

On the interlayer spacing collapse of Cloisite 30B organoclay

When used as a nanofiller for the preparation of polymer/clay nanocomposites (PCNs), Cloisite^® 30B (30B) often undergoes a d-spacing collapse, as demonstrated by a shift to wider angles of the XRD basal reflection. Such collapse has been variously attributed to organoclay contamination or, more often, to thermal degradation of the organic modifier with expulsion of the volatile products from the galleries. In this work, several PCNs loaded with 30B have been prepared by melt compounding, using different polymer matrices, and have subsequently been subjected to dissolution in appropriate solvents followed by precipitation in excess non-solvent and room temperature drying. An XRD analysis of the products has shown that this treatment makes the 30B basal plane reflection go back to the original angular position. These experiments indicate that, contrary to the situation prevailing when 30B is subjected to thermal treatments at temperatures well above the onset of degradation (∼180 °C), the d-spacing collapse observed after melt compounding 30B with polymer matrices at moderate temperatures is in fact a reversible phenomenon probably due to rearrangement of the alkyl chains of the clay modifier in a disposition intermediate between bilayer and monolayer.     

Evaluation of steviol and its glycosides in Stevia rebaudiana leaves and commercial sweetener by ultra-high-performance liquid chromatography-mass spectrometry

Stevia rebaudiana leaves contain non-cariogenic and non-caloric sweeteners (steviol-glycosides) whose consumption could exert beneficial effects on human health. Steviol-glycosides are considered safe; nonetheless, studies on animals highlighted adverse effects attributed to the aglycone steviol. The aim of the present study was to develop and validate two different ultra-high-performance liquid chromatography methods with electrospray ionization mass spectrometry (UHPLC-MS) to evaluate steviol-glycosides or steviol in Stevia leaves and commercial sweetener (Truvia^®). Steviol-glycosides identity was preliminarily established by UV spectra comparison, molecular ion and product ions evaluation, while routine analyses were carried out in single ion reaction (SIR) monitoring their negative chloride adducts. Samples were sequentially extracted by methanol, cleaned-up by SPE cartridge and the analytes separated by UHPLC HSS C₁₈ column (150 mm × 2.1 mm I.D., 1.8 μm). The use of CH₂Cl₂ added to the mobile phase as source of Cl⁻ enhance sensitivity. The LLOD for stevioside, rebaudioside A, steviolbioside and steviol was 15, 50, 10 and 1 ng ml⁻¹, respectively. Assay validation demonstrated good performances in terms of accuracy (89–103%), precision (<4.3%), repeatability (<5.7%) and linearity (40–180 mg/g). Stevioside (5.8 ± 1.3%), rebaudioside A (1.8 ± 1.2%) and rebaudioside C (1.3 ± 1.4%) were the most abundant steviol-glycosides found in samples of Stevia (n = 10) from southern Italy. Rebaudioside A was the main steviol-glycosides found in Truvia^® (0.84 ± 0.03%). The amounts of steviol-glycosides obtained by the UHPLC-MS method matched those given by the traditional LC-NH₂-UV method. Steviol was found in all the leaves extract (2.7–13.2 mg kg⁻¹) but was not detected in Truvia^® (<1 μg kg⁻¹). The proposed UHPLC-MS methods can be applied for the routine quality control of Stevia leaves and their commercial preparations.     

A multiwalled carbon nanotube/dihydropyran composite film electrode for insulin detection in a microphysiometer chamber

We have developed a multiwalled carbon nanotube/dihydropyran (MWCNT/DHP) composite sensor for the electrochemical detection of insulin in a microfluidic device. This sensor has been employed for physiological measurements of secreted insulin from pancreatic islets in a Cytosensor^® previously modified to be a multianalyte microphysiometer (MAMP). When compared with other established electrochemical insulin sensors, the MWCNT/DHP composite film sensor presented improved resistance to fluidic shear forces, while achieving enhanced electrode kinetics. In addition, the preparation of the composite film is straightforward and facile with a self-polymerizing monomer, DHP, used to add mechanical stability to the film. The sensor film was able to detect insulin concentrations as low as 1 μM in the MAMP during calibration experiments. The MWCNT/DHP composite sensor has been successfully used for the direct detection of insulin secreted by islets in the microphysiometer.     

Validation of a direct non-destructive quantitative analysis of amiodarone hydrochloride in Angoron formulations using FT-Raman spectroscopy

Raman spectroscopy was applied for the direct non-destructive analysis of amiodarone hydrochloride (ADH), the active ingredient of the liquid formulation Angoron^®. The FT-Raman spectra were obtained through the un-broken as-received ampoules of Angoron^®. Using the most intense vibration of the active pharmaceutical ingredient (API) at 1568 cm⁻¹, a calibration model, based on solutions with known concentrations, was developed. The model was applied to the Raman spectra recorded from three as-purchased commercial formulations of Angoron^® having nominal strength of 50 mg ml⁻¹ ADH. The average value of the API in these samples was found to be 48.56 ± 0.64 mg ml⁻¹ while the detection limit of the proposed technique was found to be 2.11 mg ml⁻¹. The results were compared to those obtained from the application of HPLC using the methodology described in the European Pharmacopoeia and found to be in excellent agreement. The proposed analytical methodology was also validated by evaluating the linearity of the calibration line as well as its accuracy and precision. The main advantage of Raman spectroscopy over HPLC method during routine analysis is that it is considerably faster and no solvent consuming. Furthermore, Raman spectroscopy is non-destructive for the sample. However, the detection limit for Raman spectroscopy is much higher than the corresponding for the HPLC methodology.     

A model for methanol transport through Nafion membrane in diffusion cell

The transport of methanol through Nafion^® membrane in diffusion cell is investigated using the open circuit potential method at different initial methanol concentration solutions. A simple mathematical model based on quasi-steady-state diffusion for the transport of methanol across the membrane in a diffusion cell is developed to simulate the experimental data in order to measure the methanol permeability. The influence of the diffusion cell parameters and thickness of the membrane on the methanol permeability measurement has been evaluated and analyzed. By means of Maclaurin expansion technique, this model can be used to predict the deviation of methanol permeability determined by steady-state diffusion model.     

The effect of spatial confinement of Nafion in porous membranes on macroscopic properties of the membrane

Polyelectrolytes were incorporated into porous reinforcing materials to study the properties of ionomers in confined spaces and to determine the effect of the porous material on the behaviour of the membranes. Nafion^® was imbibed into porous polypropylene (Celgard^®), ultra-high-molecular weight polyethylene (Daramic^®), and polytetrafluoroethylene (PTFE) films. Through the use of reinforcing materials, it is possible to prepare membranes that are thinner, but stronger than pure ionomer membranes. Thin reinforced membranes have advantages such as lower areal resistance (as low as 0.14 Ω cm² for 57 μm CG3501 + Nafion^® compared to 0.34 Ω cm² for 89 μm cast Nafion^®) and lower dimensional changes due to swelling (as low as a 4% change in length and width for WDM + Nafion^® compared to 13% for cast Nafion^®). Using reinforcing materials results in a reduction in important membrane properties compared to bulk Nafion^®, such as proton conductivity (as low as 0.016 S cm⁻¹ for CG3401 + Nafion^® compared to 0.076 S cm⁻¹ for cast Nafion^®), effective proton mobility (as low as 3.2 × 10⁻⁴ cm² V⁻¹ s⁻¹ CG3401 + Nafion^® compared to 7.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ for cast Nafion^®), and water vapour permeance (as low as 0.036 g h⁻¹ Pa⁻¹ m⁻² for WDM + Nafion^® compared to 0.056 g h⁻¹ Pa⁻¹ m⁻² for cast Nafion^®). By normalizing the membrane properties with respect to ionomer content, it was possible to examine the properties of the Nafion^® inside the pores of the membranes. The proton conductivity (as low as 0.032 S cm⁻¹ for CG3401 + Nafion^®), effective proton mobility (as low as 3.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ for CG3401 + Nafion^®), and water vapour permeability (as low as 2.7 × 10⁻⁶ g h⁻¹ Pa⁻¹ m⁻¹ for PTFE MP 0.1 + Nafion^®) of the ionomer in the membrane are also diminished compared to bulk Nafion^® due to decreased connectivity of the ionomer and a restriction in macromolecular motions caused by the pore walls. A series of porous materials with increasing pore were also examined. As the pore size of the PTFE MP materials increased from 0.1 μm to 10 μm, the proton conductivity (0.022 S cm⁻¹ to 0.041 S cm⁻¹), effective proton mobility ((4.1 to 5.6) × 10⁻⁴ cm² V⁻¹ s⁻¹), and water vapour permeability ((2.4 to 4.3) × 10⁻⁶ g h⁻¹ Pa⁻¹ m⁻¹) of the reinforced membranes improved with increasing pore size and the properties of the ionomer inside the membranes approached the value of bulk Nafion^®.     

Tetradecyl(trihexyl)phosphonium chloride ionic liquid single-drop microextraction for electrothermal atomic absorption spectrometric determination of lead in water samples

A highly efficient single-drop microextraction (SDME) procedure using a low-cost room temperature ionic liquid (RTIL), i.e., tetradecyl(trihexyl)phosphonium chloride (CYPHOS^® IL 101), for Pb determination at trace levels in real water samples was developed. Lead was chelated with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) reagent and extracted into a 4 μL microdrop of CYPHOS^® IL 101. The RTIL drop was directly injected into the graphite furnace of the electrothermal atomic absorption spectrometer (ETAAS). Under optimal microextraction conditions, a preconcentration factor of 32 was achieved with only 1.5 mL of sample resulting in a phase-volume ratio of 375. The limit of detection (LOD) obtained was 3.2 ng L⁻¹ and the relative standard deviation (RSD) for 10 replicates at 0.5 μg L⁻¹ Pb²⁺ concentration level was 4.9%, calculated at peak heights. The calibration graph was linear from concentration levels near the detection limits up to at least 4.5 μg L⁻¹ with a correlation coefficient of 0.9996. The accuracy of the methodology was evaluated by analysis of a certified reference material (CRM). The method was successfully applied to the determination of Pb in tap, mineral, well and river water samples.     

A chemoenzymatic synthesis of the anti-influenza agent Tamiflu

The anti-influenza drug Tamiflu^® is synthesized from enzymatically derived, enantiomerically pure, and readily available cis-1,2-dihydrocatechol.     

Alternative protocol for oxidation in water: an effective epoxidation system promoted by the combination of Oxone and an amphiphilic ketone

Epoxidation of cyclooctene and other alkenes with Oxone^® was promoted effectively in an aqueous micellar solution of an amphiphilic ketone, which was easily derived from hepta(ethylene glycol) monodecyl ether.     

Determination of oxytetracycline in milk samples by polymer inclusion membrane separation coupled to high performance liquid chromatography

The determination of oxytetracycline in milk samples using a polymer inclusion membrane concept with high performance liquid chromatography (HPLC) was studied. The membranes developed are composed by cellulose acetate as polymer base, Cyanex 923 as carrier and o-nitrophenyl octyl ether as plasticizer. In the optimal conditions, the method exhibits good linearity in the range 0.03–0.20 mg L⁻¹ with a limit of detection and quantification of 8.2 and 27.3 μg L⁻¹ respectively. The method was successfully applied to the analysis of milk samples with high selectivity.     

Transport properties of a co-poly(amide-12-b-ethylene oxide) membrane: A comparative study between experimental and molecular modelling results

An experimental and theoretical study has been used to investigate gas diffusion and solubility in PEBAX^®2533 block copolymer membrane. Molecular simulations using COMPASS force field have been successful in predicting the gas-transport properties of a PEBAX^®2533 block copolymer and of a pure PTMO homopolymer. Gusev–Suter transition state theory (TST) and Monte Carlo methods are used for simulating the transport of five permanent gases (He, H₂, N₂, O₂, CO₂ and CH₄). Theoretical and experimental data have been compared.     

An amperometric method for the detection of amitrole, glyphosate and its aminomethyl-phosphonic acid metabolite in environmental waters using passive samplers

The herbicides amitrole and glyphosate, and its metabolite aminomethyl-phosphonic acid (AMPA), in water samples have been directly analysed by high-performance liquid chromatography using an electrochemical (EC) detector. Limits of detection of 0.3 μg mL⁻¹ for glyphosate, 0.05 μg mL⁻¹ for AMPA and 0.03 μg mL⁻¹ for amitrole were comparable to those obtained by other authors using EC and also by liquid chromatography coupled to mass spectrometry, but the latter method requires derivatisation and pre-concentration of the sample whereas EC methods show similar sensitivity without the need of any derivatisation. The method was specifically designed to analyse extracts from passive samplers used for monitoring of polar herbicide residues in waters. To this purpose, three types of Empore^® disks were tested for their ability to adsorb and desorb these ionic, polar analytes. A procedure for their extraction from the membranes and reducing the interferences from other substances present in natural waters (i.e. humic acids) is described. The method is simple, does not require sophisticated equipment and is valid for the analysis and monitoring of herbicides residues using passive samplers.