Mössbauer study of spin-glass Fe x Zn1−x F2 system

⁵⁷Fe Mössbauer effect measurements in the diluted Ising antiferromagnet Fe _x Zn_1?x F₂ withx=0.25 andx=0.57 at temperatures between 4.2 and 55 K, are reported. DC suceptibility measurements show a spin-glass (SG) phase at low temperatures forx≤0.31. Our Mössbauer spectra show a phase transition to a SG state with antiferromagnetic order (AFSG) forx=0.25 and only antiferromagnetic order forx=0.57.     

High-performance liquid chromatography and thin-layer chromatography assays for Devil's Club (Oplopanax horridus)

Devil's root, Oplopanax horridus, is a widely used folk medicine in Alaska and British Columbia. The inner bark of the root and stem has been used to treat colds, cough, fever, and diabetes. The present study involves the development of high-pressure liquid chromatography (HPLC) and thin-layer chromatography (TLC) methods to detect the presence of trans-nerolidol and sterols in the root bark. The HPLC and TLC analytical methods presented are suitable for the characterization and identification of Oplopanax horridus.     

Application of amperometric sol-gel biosensor to flow injection determination of glucose

A glucose biosensor with enzyme immobilised by sol–gel technology was constructed and evaluated. The glucose biosensor reported is based on encapsulated GOX within a sol–gel glass, prepared with 3-aminopropyltriethoxy silane, 2-(3,4-epoxycyclohexyl)-ethyltrimetoxy silane and HCl. A flow system incorporating the amperometric biosensor constructed was developed for the determination of glucose in the 1×10⁻⁴–5×10⁻³ mol l⁻¹ range with a precision of 1.5%. The results obtained for the analysis of electrolytic solution for iv administration and human serum samples showed good agreement between the proposed method and the reference procedure, with relative error <5%.     

Investigation of short lived radicals in aromatic nucleophilic substitution by use of nitroso compounds as scavengers

Radical intermediates formed in reaction of substituted nitrobenzene compounds with nucleophilic reagents have been trapped by t-nitrosobutane to yield nitroxide radicals which have been characterized in situ by ESR. The formation of short-lived radicals originating from reagents and solvents has been shown.     

Thermal and mechanical properties of PE/organoclay nanocomposites

Polyethylene/montmorillonite clay nanocomposites were obtained via direct melt intercalation. The clay was organically modified with four different types of quaternary ammonium salts. The objective of this work is to study the use of montmorillonite clay in the production of nanocomposites by means on rheological, mechanical and crystallization properties of nanocomposites and to compare to the properties of the matrix and PE/unmodified clay nanocomposites. In general, the tensile test showed that the yield strength and modulus of the nanocomposites are close to the pure PE. Apparently, the mixture with Dodigen salt seems to be more stable than the pure PE and PE/unmodified clay.     

The structure of the 1-1-difluoroethylene radical anion and the factors determining the hyperfine interaction with 19F

A structure with a pyramidal -CF₂ group is shown to desribe satisfactorily hyperfine interactions in CH₂CF_$\text{2}$ radical anions within the framework of the INDO method. The factors responsible for the substantial difference in the degree of spin density delocalization on F in CH₂CF_$\text{2}$ and C₂F_$\text{4}$ are analyzed.     

Spectrophotometric determination of zinc in copper-base alloys with TAN

TAN reacts with zinc(II) forming a red complex with composition 1:2 Zn(II)-TAN and absorption maximum at 582 nm. Zinc can be determined with this reagent in the presence of Triton X-100, in the pH range 6.20-8.00 with a molar absorptivity of 4.5×10⁴ l/mol/cm Beer's Law was obeyed up to least 1.55 g/ml. Copper interference was eliminated with a mixture of thiosulfate and ascorbic acid and nickel separated by precipitation with dimethylglyoxime. The proposed method was used for zinc determination in several copper-base alloys and the results of analysis in comparison with certified values indicated that the procedure was accurate and precise. A derivative procedure is also proposed, allowing zinc determination with high sensitivity (5-400 ng/ml).