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cInstituto de Ecología, Universidad del Mar, 70902 Puerto Ángel Oax., México Soft Independent Modeling of Class Analogy (SIMCA) e Regressão por Mínimos Quadrados Parciais foram usados nesse trabalho para a identificação e quantificação de tiamina, riboflavina, nicotinamida e piridoxina, por espectrofotometria UV-Vis, sem realizar os procedimentos analíticos de separação e pré-concentração. Para a quantificação, os intervalos de trabalho estabelecidos foram 1-14 mg L -1 para riboflavina, 2-26 mg L -1 para tiamina, 2-30 mg L -1 para nicotinamida, e 2-22 mg L -1 para piridoxina. Os resultados de recuperação obtidos foram superiores a 95% em todos os casos, para a análise de amostras sintéticas e comerciais. Na busca de cada vitamina alvo, foi construído um modelo de classificação com duas categorias: (i) com a vitamina de interesse e (ii) sem a vitamina de interesse. A capacidade discriminatória de cada modelo de classificação foi avaliada para aprendizagem, para um conjunto de amostras teste e para amostras comerciais, com resultados satisfatórios, com exceção da riboflavina. Assim, um método simples e confiável é proposto para a estimativa simultânea desses compostos.Soft Independent Modeling of Class Analogy and Partial Least Squares Regression were used in this work for the identification and quantification of thiamine, riboflavin, nicotinamide and pyridoxine by UV-Vis spectrophotometry, without separation or preconcentration steps in the analytical procedure. For quantitative purposes, the working range established was 1-14 mg L -1 for riboflavin, 2-26 mg L -1 for thiamine, 2-30 mg L -1 for nicotinamide, and 2-22 mg L -1 for pyridoxine. Recovery results higher than 95% were obtained in all cases during the analysis of synthetic and commercial samples. In the screening of each target vitamin, a classification model was built with two classes: (i) with the vitamin of interest, and (ii) without it. The discriminate capability of each classification model was evaluated for learning, independent testing and commercial samples, resulting in satisfactory findings with exception of riboflavin. Thus, a simple and reliable method is proposed for the simultaneous estimation of these compounds.

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A group of herbicides of the triazine family ͑atrazine, simazine, ametryn, prometryn, atratone, and terbutryn͒ at the water/1,2dichloroethane interface has been investigated by cyclic voltammetry. The formal transfer energy ͑⌬ o w G t,i o Ј͒ was evaluated in acidic conditions ͑pH Ͻ pK a w ͒. It was found that the chemical structure determines the transfer of these herbicides at the liquid-liquid interface. For thiotriazines the values of ⌬ o w G t,i o Ј are smaller than for chlorotriazines, indicating that the thiotrizines have more ability to protect the charge in the center of the molecule when it transfers across the interface than chlorotrizines. Ionizable triazine partition diagrams ͑potential vs pH͒ demonstrated that for all herbicides two transfer mechanisms were observed: facilitated proton transfer and ion transfer across the interface.