Coordination polymer adsorbent for matrix solid-phase dispersion extraction of pesticides during analysis of dehydrated Hyptis pectinata medicinal plant by GC/MS

The coordination polymer [Zn(BDC)(H₂O)₂]_n was tested for extraction of pyrimethanil, ametryn, dichlofluanid, tetraconazole, flumetralin, kresoxim-methyl and tebuconazole from the medicinal plant Hyptis pectinata, with analysis using gas chromatography-mass spectrometry in selected ion monitoring mode (GC/MS, SIM). Experiments carried out at different fortification levels (0.1, 0.5 and 1.0 μg g⁻¹) resulted in recoveries in the range 73-97%, and RSD values were between 5 and 12% for the [Zn(BDC)(H₂O)₂]_n sorbent. Detection and quantification limits ranged from 0.02 to 0.07 μg g⁻¹ and from 0.05 to 0.1 μg g⁻¹, respectively, for the different pesticides studied. The method developed was linear over the range tested (0.04-14.0 μg g⁻¹), with correlation coefficients ranging from 0.9987 to 0.9998. Comparison between [Zn(BDC)(H₂O)₂]_n and the commercial phase C₁₈-bonded silica showed good performance of the [Zn(BDC)(H₂O)₂]_n polymeric sorbent for the pesticides tested.     

Structure-drift time relationships in ion mobility mass spectrometry

Ion mobility spectrometry (IMS) separates ions while they travel through a buffer gas under the influence of an electrical field. The separation is affected by mass and charge but most particularly by shape (collision cross section). When coupled to MS, IMS-MS offers therefore a powerful tool for structural elucidation and isomer separation. Systematic studies aimed to compare and quantitate the effects of structural changes on drift time such as length and ramification of carbon chain, unsaturation, geometrical isomerism (cis/trans isomers for instance), cyclization and ring size are, however, scarce. Herein we used traveling wave ion mobility mass spectrometry (TWIM-MS) to systematically evaluate the relationship between structure and drift time. For that, a series of deprotonated carboxylic acids were used as model ions with a carboxylate “charge tag” for gas phase MS manipulation. Carboxylic acids showed a near linear correlation between the increase of carbon number and the increase of collision cross section (CCS). The number of double bonds changes slightly the CCS of unsaturated acids. No differences in drift time and no significant differences in CCS of cis- and trans-double bond of oleic and elaidic acids were observed. Cyclization considerably reduces the CCS. In cyclic carboxylic acids, the increase of double bonds and aromatization significantly reduces the CCS and the drift times. The use of a more polarizable drift gas, CO_2, improved in some cases the separation, as for biomarker isomers of steranoic acids. The β-isomer (cis-decaline) has smaller CCS and therefore displayed lower drift time compared to the α-isomer (trans-decaline). Structural changes revealed by calculations were correlated with trends in drift times.     

Thermal degradation of polyether-urethanes: Part 3—Polyether-urethanes prepared from methylene bis(4-phenylisocyanate) and low molecular weight poly(ethylene glycols)

Polyurethanes have been prepared by reaction of methylene bis(4-phenylisocyanate) with diethylene glycol and with poly(ethylene glycol) with a molecular weight of approximately 200. Degradation has been carried out at temperatures up to 500°C and volatile products and structural changes in the residual polymer analysed in detail. The primary degradation reaction is one of depolycondensation to form the two monomers but a large proportion of these undergo a further complex series of reactions while they diffuse from the hot reaction zone. A comprehensive mechanism for the overall process has been deduced and discussed.     

Blocking properties of gold electrodes modified with 4-nitrophenyl and 4-decylphenyl groups

The electrochemical properties of Au electrodes grafted with 4-nitrophenyl and 4-decylphenyl groups have been studied. The electrografting of gold electrode surface with aryl groups was carried out by electroreduction of the corresponding diazonium salts in acetonitrile. The nitrophenyl film growth on gold was examined by atomic force microscopy, electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy. These measurements showed that a multilayer film of nitrophenyl groups was formed. Cyclic voltammetry was used to study the blocking properties of aryl-modified gold electrodes towards the Fe(CN)₆^3−/4− redox system. The reduction of oxygen was strongly suppressed on these electrodes as evidenced by the rotating disc electrode results.     

Geographic origin of southern Brazilian wines by carbon and oxygen isotope analyses

We present a method that can differentiate between the varieties of grapes and the vintages of wines and show the relationship between the grapes, the wine and the geographic location. The place of origin and its geographic and climatic characteristics were determined by the isotopic ratios, ¹³C/¹²C of the ethanol and ¹⁸O/¹⁶O of the water content of wine (wine water), for southern Brazil wines. The producing subregions of Pinto Bandeira, Vale dos Vinhedos and Nova Pádua showed differences in the temperature, rainfall and humidity conditions used for the production under microvinification conditions of Merlot and Cabernet Sauvignon varieties, in the harvests of 2005 and 2006. An isotope ratio mass spectrometer coupled to an elemental analyzer was used to measure the ¹³C/¹²C of ethanol and the ¹⁸O/¹⁶O of wine water. Regardless of the grape variety used, it was possible to determine the subregion through measurement of the δ¹⁸O values in both harvests. The altitudes of the different subregions led to statistical differences and demonstrated an influence mainly on the δ¹⁸O values of wine water. The δ¹⁸O value of wine water was determined to be more selective for the determination of the cultivation subregions than the δ¹³C value of the ethanol. The altitude and latitude influenced mainly the δ ¹⁸O values of wine water and the ethanol. The climatic influences are more noteworthy in distinguishing the year of the harvest than the cultivation subregion. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of silica–silver wires by a sol–gel technique

SiO₂–Ag wires were synthesized by a sol–gel technique. A two step approach was followed, focusing mainly on the effect of acid concentration on the first stage and processing temperature on the second. This acid-catalyzed reaction on the first stage yielded SiO₂–AgCl wires with diameters as low as 800 nm average, and lengths ranging up to 100 μm, as determined by LV-SEM and TEM. A thermal treatment at different temperatures on the second step, under H₂ atmosphere, yields silica–silver unidirectional structures. The chemical composition of these structures was determined by EDS, indicating the presence of Si, O and Ag. The transformation of the wires as a function of temperature under reducing atmosphere was followed by electron microscopy analysis. At 400 °C and above the silica starts to cover the reduced silver while maintaining the unidirectional conformation, suggesting a tendency to form silver wires covered by a silica layer.     

Critical review on analytical methods for biodiesel characterization

Biodiesel is an alternative fuel composed of mono-alkyl esters and obtained mainly from the base-catalyzed transesterification reaction of oils or fats. Its use (pure or blended) does not demand any modification in the diesel engine and in the existing fuel distribution and storage infrastructure. Moreover, biodiesel has a high energetic yield, fixes the solar energy and contains insignificant amounts of sulphur. Therefore, biodiesel is currently the best substitute for fossil diesel fuel.Besides mono-alkyl esters, glycerol (main co-product), alcohol, catalyst, free fatty acids, tri-, di- and monoglycerides compose the final mixture of biodiesel production process. These and other kinds of contaminants can lead to severe operational and environmental problems. Therefore, the quality control of biodiesel is greatly significant to the success of its commercialization and market acceptance. Some important issues on the biodiesel quality control involve the monitoring of transesterification reaction, the quantification of mono-alkyl esters and free- and bonded glycerol as well as determination of residual catalysts and alcohol. Moreover, the determination of blend levels is another key aspect of biodiesel analyses. Chromatography and spectroscopy are the analytical methods most used for the biodiesel characterization, but procedures based on physical properties are also available.Previously, a review on analytical methods used to evaluate biodiesel quality was written by Knothe. Due to the importance of this field, we made an update of Knothes’ review. Therefore, in this paper, we will describe new developments in biodiesel analyses and some references showed in Knothes’ paper. Specially, we will describe analytical methods used for quantification of glycerol, mono-, di-, triglycerides, methanol, water, Na, K, P, and steroids in biodiesel or along the transesterification reaction. Also, the determination of biodiesel content in blends and some physicochemical parameters are discussed. At the end, we will assess the available techniques and point out some improvements on analytical methods for biodiesel characterization.     

Quantification of Cyclobutane Pyrimidine Dimers Induced by UVB Radiation in Conidia of the Fungi Aspergillus fumigatus,Aspergillus nidulans,Metarhizium acridum and Metarhizium robertsii

Conidia are responsible for reproduction, dispersal, environmental persistence and host infection of many fungal species. One of the main environmental factors that can kill and/or damage conidia is solar UV radiation. Cyclobutane pyrimidine dimers (CPD) are the major DNA photoproducts induced by UVB. We examined the conidial germination kinetics and the occurrence of CPD in DNA of conidia exposed to different doses of UVB radiation. Conidia of Aspergillus fumigatus, Aspergillus nidulans and Metarhizium acridum were exposed to UVB doses of 0.9, 1.8, 3.6 and 5.4 kJ m⁻². CPD were quantified using T4 endonuclease V and alkaline agarose gel electrophoresis. Most of the doses were sublethal for all three species. Exposures to UVB delayed conidial germination and the delays were directly related both to UVB doses and CPD frequencies. The frequencies of dimers also were linear and directly proportional to the UVB doses, but the CPD yields differed among species. We also evaluated the impact of conidial pigmentation on germination and CPD induction on Metarhizium robertsii. The frequency of dimers in an albino mutant was approximately 10 times higher than of its green wild-type parent strain after exposure to a sublethal dose (1.8 kJ m⁻²) of UVB radiation.     

Determination of formaldehyde by flow injection analysis with spectrophotometric detection exploiting brilliant green-sulphite reaction

A method for the determination of formaldehyde by flow injection analysis with spectrophotometric detection is proposed, based on retarding the reaction between brilliant green and sulphite by the addition of formaldehyde; this was investigated for formaldehyde quantification in extracts from wood-based panels. For the first time, a heating step was explored, providing a sample throughput of 50 analyses per hour, with a limit of detection of 0.02 mg L^?1 and linearity of 0.20–3.0 mg L^?1, which was adequate for the expected range of formaldehyde concentration in the extracts. The mean recovery observed for actual samples was in the range of 92–106 %, with a maximum relative standard deviation of 6.0 %. The paired t-test revealed no significant difference between this method and the official Nash method, demonstrating an appropriate accuracy and precision; the method is proposed as a simple, fast and inexpensive alternative for the routine determination of formaldehyde in an aqueous medium.