Actions de groupes de Kazhdan sur le cercle

We prove that every homomorphism from a discrete Kazhdan group to the group of orientation-preserving diffeomorphisms of the circle of class C^1+α (α>1/2) has a finite image.     

Variable-angle synchronous fluorescence spectrometry and rank annihilation methods for mixture resolution

The potential of variable angle synchronous spectroscopy (VASS) for fluorescent mixtures resolution was assessed and compared with the rank annihilation method (RAM). For this purpose, a set of excitation-emission matrices from three standard cyclodextrin fluorescence-enhanced solutions of the pesticides aminocarb, carbendazim and coumatetralyl and a mixture of them was obtained. Careful selection of the spectral routes to be scanned provides analyte signals that are free of interferences. Application of the rank annihilation method to excitation-emission matrices (EEMs) obtained by conventional scanning spectrofluorimetry gives quantitative results that show poor precision and accuracy when compared to those of VASS. The recoveries from ternary mixtures by VASS are within 99-104% and by RAM within 84-130%.     

Rapid ultraviolet spectrophotometric and liquid chromatographic methods for the determination of natamycin in lactoserum matrix

Two rapid and simple methods were developed for the determination of natamycin in lactoserum matrix by ultraviolet (UV) spectrophotometry and liquid chromatography (LC) with diode-array detection. The methods involve protein precipitation with methanol, followed by centrifugation. No cleanup is necessary. The applicable concentrations of natamycin in lactoserum range from 2 to 500 mg/L for samples analyzed by both methods. The detection and quantitation limits are 0.07 and 0.23 mg/L, respectively, for the UV spectrophotometric method and 0.1 and 0.32 mg/L, respectively, for the LC method. The methods were applied satisfactorily to the determination of natamycin in various commercial lactosera. Both methods were validated independently by standard additions and Youden methodologies, which verified their accuracy. Once the 2 proposed methods were validated independently, the validation of one method was carried out with the other.     

Simultaneous determination of quinoline yellow and brilliant blue FCF in cosmetics by solid-phase spectrophotometry

A method for the simultaneous determination of quinoline yellow (QY) and brilliant blue FCF (BB) in mixtures by solid-phase spectrophotometry has been developed. Both colorants were isolated in Sephadex DEAE A-25 gel showing maximum absorbances at 632 nm and 415 nm for BB and QY respectively. The applicable concentration ranges were between 25.0 and 500.0 mug 1(-1) for BB and between 50.0 and 750.0 mug 1(-1) for QY. The detection limits were 6.1 and 13.4 mug (-1) for BB and QY respectively. Application of the method to real samples (colognes, after shave lotions and shampoo gels) involves a previous extraction process of the colorants before their isolation on the gel.     

Photometric and fluorimetric kinetic determination of manganese by means of the oxidation of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2,6-disulphonate

Three kinetic methods for the determination of manganese, two of them by photometric monitoring and another by fluorimetric monitoring, based on the oxidation of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2,6-disulphonate are described. A critical comparative evaluation of both monitoring techniques and their effect on the analytical figures of merit of the methods has been made. Manganese contents between 6.5 and 21.7 ng ml can be determined with relative standard deviation of +/- 3.7%. Under appropriate working conditions, the fluorimetric method can be satisfactorily applied to the determination of manganese in environmental samples of tap water and workroom metallic fumes.