Método Multiresiduo para determinar Pesticidas en Frutas por Extracción con Fluido Supercrítico

A rapid and reliable method for the determination of 25 compounds selected from four classes of pesticides in samples of fresh apples, grapes, pears, and strawberries purchased at a local supermarket, is presented. The study describes two different methods of extraction: solid-liquid extraction with acetone and supercritical fluid extraction. Clean-up was based on aminopropyl cartridge extraction followed by gas chromatography with an electron capture detector for simultaneous determinations. Confirmatory analysis was carried out by gas chromatography with mass spectrometry in the selected-ion monitoring (SIM) mode. Extraction efficiencies were directly compared and the methods were applied to the analysis of real samples. Recoveries for a majority of pesticides from standard samples at enrichment levels of 0.04-0.10 mg/ kg ranged from 77 to 96 % for both methods. The supercritical fluid extraction method showed good limits of detection (less than 0.01 mg/kg, depending on the pesticide and matrix) as well as minimizing environmental concerns, time, and laboratory effort. © 2006 Centro de Información Tecnológica

Determination of 2,4-D and dicamba in food crops by MEKC

The determination of 2,4-D (2,4-dichlorophenoxyacetic acid) and Dicamba (2-methoxy-3,6-dichlorobenzoic acid) residues in sugar cane, rice and corn was performed by a supercritical fluid extraction (SFE) method using CO2/acetone as extraction mix and an SFE apparatus developed in our laboratory. The extracts were cleaned up after extraction by both liquid- liquid partition and a Florisil column. Micellar electrokinetic capillary chromatography (MEKC) coupled with ultraviolet on-column detection was used for the analysis of these pesticides. The detection limits were improved by the preparation of a special detection cell with an increased pathlength that gave detection limits of ca. 0.6 pg for 2,4-D and Dicamba. Our results demonstrated that capillary electrophoresis can be a powerful new analytical tool for pesticide residue analysis

NOVAS APLICAÇÕES DE SISTEMAS DE PARA EXTRAÇÃO COM FLUIDO SUPERCRÍTICO (SFE)" HOME-MADE".: VI. CONTROLE DE AGROTÓXICOS EM PRODUTOS ALIMENTÍCIOS

No presente trabalho apresentamos um sistema para extração com fluido supercrítico (SFE)" home-made" utilizado em extrações de resíduos de pesticidas de diversas matrizes. Os pesticidas estudados foram extraídos usando-se como fluido extrator CO2 no estado supercrítico com ou sem modificadores. Os resultados obtidos mostraram-se mais vantajosos do que aqueles obtidos por métodos convencionais de extração

Leakage current, ferroelectric and structural properties in Pb(1-x)Ba(x)TiO(3) thin films prepared by chemical route

Single-phase perovskite structure Pb(1-x)Ba(x)TiO(3) thin films (x = 0.30, 0.50 and 0.70) were deposited on Pt/Ti/SiO(2)/Si substrates by the spin-coating technique. The dielectric study reveals that the thin films undergo a diffuse type ferroelectric phase transition, which shows a broad peak. An increase of the diffusivity degree with the increasing Barium contents was observed, and it was associated to a grain decrease in the studied composition range. The temperature dependence of the phonon frequencies was used to characterize the phase transition temperatures. Raman modes persist above tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of breakdown of the local cubic symmetry by chemical disorder. The absence of a well-defined transition temperature and the presence of broad bands in some interval temperature above FE-PE phase transition temperature Suggested a diffuse type phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in these thin films. The leakage Current density of the PBT thin films was studied at different temperatures and the data follow the Schottky emission model. Through this analysis the Schottky barrier height values 0.75, 0.53 and 0.34 eV were obtained to the PBT70, PBT50 and PBT30 thin films, respectively. (C) 2008 Elsevier Ltd. All rights reserved.FAPESP/CEPID. FAPESP[06/53926-4]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP