Solange Leite de Moraes

Determinação da concentração micelar crítica de ácidos húmicos por medidas de condutividade e espectroscopia

The aim of this study was the determination of the critical micelle concentration (CMC) of the sodium dodecyl sulfate (SDS) surfactant using spectroscopic and conductimetric determinations and to compare these methodologies in the determination of the CMC of different humic acids (HA). The CMC obtained by conductimetric determination was satisfactory. By spectroscopic determination two values of the CMC were obtained for HA. These values can be to due the intra and intermolecular interactions in the HA structure.

Capillary electrophoresis (CE): a powerful tool to characterize humic acid (HA)

The present study evaluates the possibility of eliminating the purification steps involved in the characterization of HA by capillary zone electrophoresis (CZE). The HAs of various sources were analyzed, showing different electropherograms by CZE, which depend on the charge and size of HA. The data suggest that the purification of the sample is not necessary to characterize HAs. Based on the results, CZE showed to be a promising tool to characterize HA of different origins without the purification step of the sample.

Estratégias de pré-concentração em eletroforese capilar (CE): parte 1. Manipulação da velocidade eletroforética do analito

Capillary electrophoresis has become a well-established and routine-based separation technique. It is based on the differences between charged analyte mobility in aqueous or organic electrolytes. Its major limitation is the sensitivity due to small sample injection volumes and the narrow diameter of the capillaries, especially when UV detection is used. There are a number of ways to increase the concentration sensitivity. This report shows some on-line preconcentration strategies to perform it in free solution capillary electrophoresis that are based on manipulation of the analyte electrophoretic velocity during the sample introduction (stacking, field amplification and transient isotachophoresis).

Multiresidue Screening Methods for the Determination of Pesticides in Tomatoes

The possibility of applying thin layer chromatography (TLC) detection for the analysis of pesticide residues in tomatoes was investigated. Samples of tomatoes that have never been treated with pesticide were fortified with atrazine, carbaryl, carbofuran, chloroxuron, diuron, dimethoate, imazalil, oxamyl and methamidophos. The samples were extracted, cleaned‐up by gel permeation chromatography and then applied on silica gel plates. The pesticides were eluted with ethyl acetate and dichloromethane. Two eluting solvent systems were tested, one using the reagents o‐ toluidine + potassium iodite (o‐TKI) and the other p‐ nitrobenzene fluoroborate (NBFB). After the development of the plates, the diameter of the spots was measured. The lowest minimum detection quantity (MDQ) for o‐TKI system for atrazine was 12 ng. The highest was 125 ng for carbofuran. Using NBFB system, the lowest MDQ was 60 ng for carbaryl and the highest was 70 ng obtained for carbofuran. Considering the concentration of these pesticides in the spiked tomato samples, the minimum concentration was 1.1 ng/µL and 32.3 ng/µL for atrazine and carbofuran, respectively, by using o‐TKI system. For NBFB system the minimum concentration reached was 3.5 ng/µL and 4.3 ng/µL for carbaryl and carbofuran, respectively. This study showed that TLC can be used for semi‐quantitative analysis.

Análise de resíduos de pesticidas em tomates por cromatografia em camada delgada

Pesticide residues are determined by thin layer chromatography (TLC) using the Hill reaction as a detection method. Tomatoes samples without pesticide were fortified with atrazine, diuron, chloroxuron and metribuzin, and were applyed in silica gel plates with the help of a microsyringe. The pesticides were elued with ethyl acetate. There was no need of cleaning up because no interference was noticed. After the revelation of the plates, the diameters of the spots were measure by using a rule. The range of the determined concentration for all the pesticides was from 0.1 to1.0 ng/mL. The results obtained through TLC can be used for semi-quantitative analysis.The results obtained were compared to gas and liquid chromatography, showing good agreement between both techniques.

Chemical Constituents of the Ethanolic Extract of Mikania parodii

CEP 14040-901, Ribeirao Preto, SP, Brazil; 2) Faculdade de Ciencias Farmaceuticas de Ribeirao Preto, Universidade de Sao Paulo, Via do Cafe s/n, CEP 14040-903, Ribeirao Preto, SP, Brazil, fax: +55 16 3602 4243, e-mail: drolivei@fcfrp.usp.br; 3) Centro Nacional de Pesquisa e Gado de Corte–CNPGC/EMBRAPA, Rodovia BR-262, km-04, Caixa Postal 154, CEP 79002970 Campo Grande, MS, Brazil. Published in Khimiya Prirodnykh Soedinenii, No. 4, p. 413, July-August, 2008. Original article submitted February 12, 2007.