Immunoaffinity-based extraction of phenylurea herbicides using mixed antibodies against isoproturon and chlortoluron

Summary The analysis of several phenylurea herbicides in different waters is described using an immunoaffinity column clean-up and determination by high performance liquid chromatography. The pesticides were selectively retained on a solid phase extraction column containing antibodies to chlortoluron and to isoproturon immobilised onto silica. Selected phenylureas were eluted using a simple phosphate buffered saline/ethanol mixture at low pH. The immunoaffinity approach gave extracts free of interfering substances and allowed detection limits comparable to those required for pesticides in water in the European Community. The proposed method was successfully applied to the determination of chlortoluron, isoproturon, linuron and chlorbromuron in tap and river water. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Flotation-spectrophotometric method for the determination of mercury using iodide and brilliant green

This paper describes a sensitive spectrophotometric method for the determination of mercury, based on the flotation of a mercury iodide-brilliant green complex with cyclohexane at pH 5 and dissolution of the complex in acetone. The absorbance of the complex is measured at 625 nm. Beer's law is obeyed from 4–500 g/l of mercury. The method is highly sensitive ( = 5.96 × 10⁵ 1 mol^–1 cm^–1) and selective, as it is free from interferences by almost all cations and anions in the presence of EDTA. Furthermore, a two-level orthogonal array design as a chemometric method has been used for optimization of the various parameters involved. The method has been successfully applied to paper industry effluents.     

Natural benzofurans. Synthesis of medicagol methoxybenzofuran

A general route to 2-arylbenzofurans, consisting of reaction of an o-halogenophenol ester with a cuprous arylacetylide, was employed to synthesize medicagol methoxybenzofuran. 2,4-Diraethoxyacetophenone was converted to 2,4-dimethoxyphenylacetylene in three steps and reaction of the cuprous salt with 2-iodo-4,5-methylenedioxyphenyl acetate gave the desired 2-(2′,4′-dimethoxyphenyl)-5,6-methylenedioxybenzofuran.     

Composition-controlled synthesis of bimetallic gold-silver nanoparticles

This paper reports findings of an investigation of the synthesis of monolayer-capped binary gold-silver (AuAg) bimetallic nanoparticles that is aimed at understanding the control factors governing the formation of the bimetallic compositions. The synthesis of alkanethiolate-capped AuAg nanoparticles was carried out using two related synthetic protocols using aqueous sodium borohydride as a reducing agent. One involves a two-phase reduction of AuCl(4)(-), which is dissolved in organic solution, and Ag(+), which is dissolved in aqueous solution. The other protocol involves a two-phase reduction of AuCl(4)(-) and AgBr(2)(-), both of which are dissolved in the same organic solution. AuAg nanoparticles of 2-3 nm core sizes with different compositions in the range of 0-100% Au have been synthesized. The two synthetic routes were compared in terms of bimetallic composition and size properties. Our new findings have allowed us to establish the correlation between synthetic feeding of metals and metal compositions in the bimetallic nanoparticles, which have important implications to the exploration of gold-based bimetallic nanoparticles for constructing sensing and catalytic nanomaterials.     

Permittivity and AC conductivity in yttria-stabilized zirconia

Alternating current (ac) conductivity and permittivity measurements were carried out on yttriastabilized cubic zirconia, with yttria varying from 9.6 to 25.5 mol%. In this composition range, the dielectric constant measured at 10³ Hz decreased from 29.8 to 23.2 as the yttria concentration increased. A plot of the ac conductivity versus frequency exhibited a plateau conductivity (_dc) and a frequency () dependent term '(). An analysis of '() with a suitable theoretical approach based on a pairs-approximation model, resulted in a calculated binding energy for the yttrium-associated oxygen vacancy of 0.29±0.05 eV, which compares favorably with values obtained by different means in previous studies. The experimental determination of the frequency dependence of the conductivity and its analysis provides an effective basis for understanding the ionic conductivity mechanism.     

Spectrophotometric determination of ziram (dithiocarbamate fungicide) by thiocyanate and rhodamine 6G method

A sensitive spectrophotometric method has been developed for the determination of ziram in water, vegetables and grains. The method is based on the dissociation of dithiocarbamate complex of zinc with thiocyanate and rhodamine 6G at pH 4 to form a pink coloured complex that is stabilized by gelatin. The method is simple and Beer's law is obeyed over the concentration range of 0.05-1 ppm of ziram. The method is free from interference of similar dithiocarbamate fungicides containing Mn(2+) and Fe(3+) ions.     

Self-avoiding walks and trees in spread-out lattices

LetG _R be the graph obtained by joining all sites ofZ ^d which are separated by a distance of at mostR. Let (G _R ) denote the connective constant for counting the self-avoiding walks in this graph. Let (G _R ) denote the coprresponding constant for counting the trees embedded inG _R . Then asR, (G _R ) is asymptotic to the coordination numberk _R ofG _R , while (G _R ) is asymptotic toek _R. However, ifd is 1 or 2, then (G _R )-k _R diverges to –.Dedicated to Oliver Penrose on this occasion of his 65th birthday.     

Rapid separation of microgram amounts of metal ions on stannic antimonate ion-exchange paper

Summary Microgram amounts of metal ions have been separated using stannic antimonate paper. Most of the separations can be accomplished within 15 minutes.

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Zusammenfassung Unter Verwendung von Zinn(IV)antimonat-Papier lassen sich Mikromengen zahlreicher Metallionen trennen. Die meisten Trennungen lassen sich innerhalb 15 min durchführen.