Polarographic determination of herbicide thifensulfuron methyl/application to agrochemical pesticide,soil, and fruit juice

A novel, sensitive, simple, fast, and fully validated differential pulse polarographic (DPP) method for the determination of trace amounts of thifensulfuron-methyl in pesticide formulation, soil, and orange juice is reported. This procedure was based on a highly sensitive peak formed due to the reduction of thifensulfuron-methyl on a dropping mercury electrode over the pH range 1.00–10.00 in Britton–Robinson buffer. The polarographic reduction exhibits only a single peak in the pH ranges pH?≥?3.0 and pH?≤?6.0 and pH?=?10.0 located at potential values of ?1.010, ?1.350, and ?1.610?V (vs. SCE), respectively. The single peak appeared as a maximum at pH 3.0 (?1.010?V) was well resolved and suitable to be investigated for analytical use. This peak showed quantitative increments with the additions of standard thifensulfuron-methyl solution under the optimal conditions, and the cathodic peak current was linearity proportional to the thifensulfuron-methyl concentration in the range of 2?×?10^?7–5?×?10^?5?M. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 1.05?×?10^?7 and 3.50?×?10^?7?M, respectively, according to the relation k ?×?SD/b (where k?=?3 for LOD, k?=?10 for LOQ, SD is the standard deviation of the blank, and b is the slope of the calibration curve). The proposed method was applied to pesticide formulation (Harmony® Extra), and the average percentage recovery was in agreement with that obtained by the spectrophotometric comparison method, 97.82 and 102.6%, respectively. The method was extended to determination of thifensulfuron-methy in spiked soil and orange juice, showing a good reproducibility and accuracy with a relative standard deviation of 4.55 and 1.40%, and relative errors of +2.80 and +1.90%, respectively.     

Square wave voltammetric determination of diafenthiuron and its application to water,soil and insecticide formulation

A square wave cathodic stripping voltammetric (SWCSV) method has been developed for the determination of insecticide diafenthiuron. The procedure is based on controlled accumulation of the insecticide on a static hanging mercury drop electrode (SHMDE) at 0.00?mV (vs. Ag/AgCl) in Britton-Robinson buffer solution (pH 7.0). The insoluble mercury compound was reduced at ?510?mV during the cathodic potential scan. The peak currents were linearly related to insecticide concentration between 30.4 and 3200?µg?L^?1 . The detection and quantification limit were 9.1?µg?L^?1 and 30.4?µg?L^?1, respectively. The proposed analytical procedure was applied to natural water and soil samples. The method was extended to direct determination of diafenthiuron in insecticide formulation Polo® 50 WP and average content of 50.3?±?1.7 (m/m) at 90% confidence level, in close agreement with the 50.0% quoted by the manufacturer. HPLC comparison method indicated that accuracy was in agreement with that obtained by the proposed method.     

Random-covariances and mixed-effects models for imputing multivariate multilevel continuous data

Principled techniques for incomplete-data problems are increasingly part of mainstream statistical practice. Among many proposed techniques so far, inference by multiple imputation (MI) has emerged as one of the most popular. While many strategies leading to inference by MI are available in cross-sectional settings, the same richness does not exist in multilevel applications. The limited methods available for multilevel applications rely on the multivariate adaptations of mixed-effects models. This approach preserves the mean structure across clusters and incorporates distinct variance components into the imputation process. In this paper, I add to these methods by considering a random covariance structure and develop computational algorithms. The attraction of this new imputation modeling strategy is to correctly reflect the mean and variance structure of the joint distribution of the data, and allow the covariances differ across the clusters. Using Markov Chain Monte Carlo techniques, a predictive distribution of missing data given observed data is simulated leading to creation of multiple imputations. To circumvent the large sample size requirement to support independent covariance estimates for the level-1 error term, I consider distributional impositions mimicking random-effects distributions assigned a priori. These techniques are illustrated in an example exploring relationships between victimization and individual and contextual level factors that raise the risk of violent crime.     

Experimental study on impulsive synchronization between two modified Chua's circuits

As in many continuous synchronization studies and chaos-based communication systems, the paradigmatic chaos generator, Chua's circuit has been generally used in impulsive synchronization schemes. On the other hand, different versions of Chua's circuit are considered in literature. Nowadays, we realized a new version of Chua's circuit by modifying circuit connections and inserting an additional passive element to the circuit structure. In this study, we have experimentally investigated impulsive synchronization between two modified Chua's circuits. Experimental results show that impulsive synchronization is achieved in the proposed scheme with respect to the switching frequency.     

Functionalized polymers for high-resolution photolithography

Polymers obtained by radical polymerization of maleic anhydride with different monomers are used in bilayer photoresists for the CARL (Chemical Amplification of Resist Lines) process. Aqueous-based silylation of resist patterns with bisaminopropyl-oligodimethylsiloxane enhances oxygen–plasma etch resistance and creates widened structures. Thus, the resolution capability of optical exposure tools can be used to the full extent and even structures beyond the optical resolution limit become accessible. Copolymerization of maleic anhydride with tBOC-maleimide or methacrylic acid t-butylester yields polymers for highly sensitive acid-catalyzed deep UV resists. With the use of a KrF excimer-laser stepper 0.25 μm structures are resolved.     

Gaspermeabilität von Polypropylen

Zusammenfassung Die Gaspermeabilität morphologisch unterschiedlicher Preßfolien aus isotaktischem Polypropylen gehorcht für He, O₂, N₂ und CO₂ unabhängig von der Polymermorphologie den Gesetzmäßigkeiten der Lösungsdiffusion. Solange das Polymermaterial keine Risse bzw. Hohlräume größerer Dimensionen enthält, wird die Gaspermeabilität der Polymerfolien mit wachsendem Kristallinitätsgrad geringer.Das Vorhandensein von Rissen ist mit einer Erhöhung des Permeabilitätskoeffizienten und einer Verringerung der Aktivierungsenergie verbunden.

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Summary The permeability of He, O₂, N₂ and CO₂ through morphological different films of isotactic polypropylene is of an activated type. In the absence of cracks and pinholes the gas permeability of the polymer films decreases with increasing crystallinity. If cracks exist the permeability coefficient increases and the energy of activation decreases.

Auszugsweise vorgetragen auf der 30. Hauptversammlung der Kolloid-Gesellschaft, 6.–9. 10. 1981 in Ulm.