Determination of herbicide residues in agricultural crops, foods, soil and water by chronometric method

Summary The method described is based on the biochemical detection of herbicides on a silica gel thin layer following their chromatographic separation. The detection reagent is a mixture of a homogenate of bean leaves (Phaseolus vulgaris) and of the redox indicator 2,6-dichloroindophenol. This chronometric determination of herbicide residues is based on the observation that dark blue inhibition zones appear on a pale yellow-green background during the exposure of the sprayed chromatoplates Silufol to light. The dark blue zones disappear again after a time, their lifetime is proportional to the amount of the herbicide in the zone.Because of the high selectivity and sensitivity of the biochemical detection this method does not require a multiple clean-up procedure, nor does it require sophisticated instrumentation. It equals gas chromatography in sensitivity and precision. The determination limit lies between 0.01 and 0.001 mg · kg^–1, the average recovery rate is 85 to 90%.

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Bestimmung der Herbicid-Rückstände in landwirtschaftlichen Produkten, in Lebensmitteln, im Boden und Wasser mit der chronometrischen Methode

Zusammenfassung Die Methode stützt sich auf einen biochemischen Nachweis der Herbicide auf einer Silicagel-Dünnschichtplatte nach ihrer chromatographischen Verteilung. Das Nachweisreagens ist eine Mischung aus einem Homogenat von Blättern der Bohnen (Phaseolus vulgaris, L.) und des Redoxindikators 2,6-Dichlorphenolindophenol. Die chronometrische Bestimmung der Herbicidrückstände gründet sich auf die Beobachtung, daß während der Lichtexposition der besprühten Dünnschichtplatte Silufol auf einem gelbgrünen Hintergrund dunkelblaue Inhibitionszoneu entstehen, welche nach einer bestimmten Zeit verschwinden. Die Haltbarkeitszeit der Zone ist der Menge des Herbicids in der Zone direkt proportionell.In Betracht der hohen Selektivität und Empfindlichkeit des biochemischen Nachweises benötigt die Methode keine komplizierte Reinigung der Extrakte und keine hochentwickelte Ausstattung des Labors mit Instrumenten. Die Empfindlichkeit und Genauigkeit der chronometrischen Methode ist gleich der der Gaschromatographie. Die Bestimmungsgrenze ist 0,01 bis 0,001 mg·kg^–1, die Wiederfindung ist 85–90%.

     

Polystyrene/polybutadiene blends: An analysis of the phase‐inversion region and cophase continuity and a comparison with theoretical predictions

Blends of polystyrene and polybutadiene were prepared by melt mixing. The melt rheology behavior of the blends was studied with a capillary rheometer. The morphology of the blends was examined with scanning electron microscopy. The levels of continuity and cocontinuity were studied by both morphology and dissolution techniques. The region of phase inversion was observed at 50 wt % polystyrene. Various theoretical models were applied to determine the region of cophase continuity and to locate the point of phase inversion. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1007–1016, 2003     

A complete quantitative model of the isothermal vapor phase epitaxy of (Hg,Cd)Te

A quantitative model of isothermal vapor phase epitaxy is proposed. It can be applied to both closed and open tube systems. This model enables the prediction of compositional profiles of the layers grown by isothermal vapor phase epitaxy with dependence on the growth parameters and thermodynamical data of the (Hg,Cd)Te system. The dependence of compositional profiles of the ISOVPE layers on temperature and time of deposition, source to substrate spacing, mercury and inert gas pressures are discussed for both solid and liquid sources. Modification of the compositional profiles by the postgrowth annealing has also been studied. The proper choice of growth and annealing parameters makes the optimization of the profiles possible. The calculated profiles are compared with the experimental data and a satisfactory quantitative fit is found in most cases. The possible reasons for remaining discrepancies are discussed.     

Study of a new energy efficient process for French fries production

A new, energy efficient production process for French fries was developed and evaluated. Superheated steam (SHS) was used for evaporation of water instead of pre-drying with air and par-frying with oil. The product was frozen by vacuum cooling. Unfortunately, with this process it was not possible to reach the quality of conventional French fries. Sensory analysis indicated that the main quality defect was a tough crust with a fatty appearance. Confocal Scanning Laser Microscopy showed that this was caused by skin formation on the surface during both SHS drying and vacuum cooling. A frying step was necessary to obtain a porous crust. A satisfactory product quality was feasible after drying with SHS instead of air. Due to the concessions made for the product quality, the final energy reduction was limited. Nevertheless, this study has gained more insight into how processing affects potato tissue on micro-scale and it has shown that a porous structure is essential for good quality French fries.     

Interactions of single-walled carbon nanotubes with monosaccharides

Closed-end single-walled carbon nanotubes were wetted in aqueous solutions of monosaccharides, forming weak surface complexes, as proven by the estimation of the content of monosaccharides in complexes isolated from aqueous solutions. The complexation was confirmed by micro-Raman spectroscopy. The Gaussian 03 (Molecular Mechanics UFF method) computations of total energy of the single-walled carbon nanotube-monosaccharides inclusion and surface complexes showed that inclusion complexes should be more stable than corresponding surface complexes. Computed total energies for particular complexes pointed to a lack of preferences for the formation of complexes with either alpha- or beta-tautomers and either pyranoses or furanoses. The forms preferred in the formation of the surface complexes usually differ from these favored in the formation of the inclusion complexes.     

Analytical study of the additives system in polyethylene

On the basis of standards of identification of substances in the additive system of polyethylene has been performed. Different methods for separation such as adsorption thin-layer chromatography, high-performance liquid chromatography with chemically bounded phases, and gas chromatography have been used. The fir al identification has been made with mass spectrometry. The substances have been extracted from polyethylene with hexane and chloroform.     

Unravelling the kinetics of the formation of acrylamide in the Maillard reaction of fructose and asparagine by multiresponse modelling

A kinetic model for the formation of acrylamide in a fructose–asparagine reaction system at initial pH 5.5 is proposed, based on an approach called multiresponse kinetic modelling. The formation of acetic acid and formic acid from the degradation of fructose and its isomer glucose was included in the proposed kinetic model. The kinetic model suggests that the effect of temperature on acrylamide formation with fructose is more due to the preceding steps with the formation of the Schiff base. The use of fructose and lower pH resulted in a higher yield of acrylamide (3%), suggesting that both can play an important role in acrylamide mitigation. Furthermore, these models have shown that, at high temperatures (120–200 °C), the Maillard reaction rapidly goes into the advanced stages, forming high amounts of organic acids and high molecular weight melanoidins. Overall, these mechanistic models provide more insight of the formation of acrylamide in a quantitative way.     

Detection of lead in Zea mays by dual‐energy X‐ray microtomography at the SYRMEP beamline of the ELETTRA synchrotron and by atomic absorption spectroscopy

This study is related to the application of the X‐ray dual‐energy microradiography technique together with the atomic absorption spectroscopy (AAS) for the detection of lead on Zea mays stem, ear, root, and leaf samples. To highlight the places with lead intake, the planar radiographs taken with monochromatic X‐ray radiation in absorption regime with photon energy below and above the absorption edge of a given chemical element, respectively, are analyzed and processed. To recognize the biological structures involved in the intake, the dual‐energy images with the lead signal have been compared with the optical images of the same Z. mays stem. The ear, stem, root, and leaf samples have also been analyzed with the AAS technique to measure the exact amount of the hyperaccumulated lead. The AAS measurement revealed that the highest intake occurred in the roots while the lowest in the maize ears and in the leaf. It seems there is a particular mechanism that protects the seeds and the leaves in the intake process. Microsc. Res. Tech., 2010. © 2009 Wiley‐Liss, Inc. This article was published online on 1 December 2009. An error was subsequently identified. This notice is included in the online and print version to indicate that both have been corrected 19 February 2010.