A procedure has been developed for simultaneous separation/preconcentration of copper, nickel, and zinc based on in situ ionic liquid-based dispersive liquid-liquid microextraction method as a prior step to their determination by flame atomic absorption spectrometry. The analytes reacted with sodium diethyl dithiocarbamate at pH 7 to form hydrophobic chelates, which were separated and preconcentrated in the ionic liquid phase. The method is fast, simple, accurate, and environmentally friendly. The parameters affecting the extraction efficiency of the proposed method such as the pH of sample solution, centrifugation time, type and volume of the dispersive solvent, and the salt effect were studied. Enrichment factors of 61.8, 61.2, and 40.0 and detection limits of 0.79, 0.93, and 0.71 µg L-1 were obtained for copper, nickel, and zinc, respectively. The relative standard deviations based on six replicate measurements were between 1.0 and 2.7%. The method was successfully applied to the extraction and determination of these metals in wastewater and alloy samples.

Resíduo de pesticida tem sido uma séria ameaça à saúde humana. Métodos de detecção rápida são necessários para os vários tipos de pesticidas. Este estudo investigou a viabilidade da combinação da espectrofotometria com o método dos mínimos quadrados parciais por boosting (boosting-PLS) para determinação simultânea de clorpirifos e carbaril, dois dos mais importantes pesticidas na agricultura. Estudou-se o efeito do pH sobre os espectros de absorbância de cada componente, sendo pH 5 o ideal. Para construir os modelos boosting-PLS, trinta e seis misturas binárias foram usadas e para validar os modelos resultantes, vinte misturas binárias foram empregadas. Resultados por boosting-PLS foram comparados com aqueles obtidos por full-spectrum PLS e algoritmo PLS acoplado a busca tabu (TS) como ferramenta de seleção de comprimento de onda. Apesar da melhoria pelas abordagens por boosting e seleção de comprimento de onda, a capacidade de previsão do algoritmo PLS, boosting-PLS mostrou-se superior aos demais modelos. Boosting-PLS não só é viável como também pode evitar a seleção de comprimento de onda.

Residue of pesticide has posed a serious threat to human health. Fast detection methods are necessary for the various types of pesticide. This study investigated the feasibility of the combination of spectrophotometry and boosting partial least squares method (boosting-PLS) for the simultaneous determination of chlorpyrifos and carbaryl, two of the most important pesticides in agriculture. Effect of pH on the absorbance spectra of each component was studied and pH 5 was selected as optimum. To build boosting-PLS models, thirty six binary mixtures were used and to validate the resulted models, twenty binary mixtures were employed. Results for boosting-PLS were compared to ones obtained for full-spectrum PLS and PLS algorithm coupled with tabu search (TS) as wavelength selection tool. In spite of the improvement by both boosting and wavelength selection approaches, the prediction ability of PLS algorithm, the boosting-PLS is superior to the other models. Boosting-PLS is not only feasible but also can avoid doing wavelength selection in such a task.