The participation of the students in the planning, execution and discussion of experimental results is important for the valuation of the role of them in the construction of the chemical knowledge implicited in the approach between education and research. This work relates either the construction of selective membrane electrodes for surfactants and its application in the potenciometric determination of the critical micellar concentration of the sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) surfactants. In adition it´s possible to discuss the potenciometric results in matching with the data valued for the tensiometric and condutimetric traditionally used in the physical-chemistry lessons.

A determinação de metais traço é um indicador importante da toxicidade dessas espécies no ambiente marinho. As técnicas de redissolução são freqüentemente utilizadas, devido a sua sensibilidade e seletividade. Nesta investigação foram determinados parâmetros eletroquímicos para a detecção da concentração dos íons de metais chumbo, zinco e cobre, em águas costeiras, empregando as técnicas de voltametria de redissolução anódica de pulso diferencial (DPASV) e voltametria de redissolução catódica adsortiva de pulso diferencial (DPACSV). Para a determinação do limite de detecção dos íons de metais foram utilizadas amostras sintéticas, em pH 2 para chumbo e zinco e em pH 9 para cobre. Na etapa de validação das metodologias realizada em amostra de água de mar costeira certificada (CASS-4) encontrou-se a concentração de 10,3 nmol L-1 para o íon Cu(II). Utilizou-se o procedimento de enriquecimento e recuperação para os metais analisados sendo obtidos os seguintes percentuais de recuperação: 95±10 (Pb2+), 110±11 (Zn2+) e 95±8 (Cu2+). Os valores de concentrações de metal total foram considerados baixos, quando comparados aos índices estabelecidos pelo CONAMA, principalmente para chumbo e zinco. Para o íon cobre a maior concentração pode ser atribuída ao uso de tintas antiincrustantes e de processos industriais.

The determination of trace metal concentrations is an important indicator of toxicity toward species present in ocean environments. Stripping techniques are frequently used, due to their sensitivity and selectivity. In this investigation we were able to determine, efficiently, the concentration of lead(II), zinc(II) and copper(II), in coastal waters, using Differential Pulse Anodic Stripping Voltammetry (DPASV) and Differential Pulse Adsorptive Cathodic Stripping Voltammetry (DPACSV) techniques. For the determination of metal ion detection limits, synthetic samples were used, pH 2 for lead and zinc and pH 9 for copper. In order to check the accuracy of the procedure a certified coastal marine sample (CASS-4) was used and a concentration of 10.3 nmol L-1 for Cu(II) was obtained. The enrichment and recovery method was used for the metals analyzed, the following percent recoveries being obtained: 95±10 (Pb2+), 110±11 (Zn2+) and 95±8 (Cu2+). The total metal concentrations obtained were considered low, when compared with the indices established by CONAMA, particularly for lead and zinc. For the copper ion the higher concentration may be attributed to its use in the anti-fouling paint, and industrial processes.

Neste trabalho foram construídos eletrodos seletivos para o surfactante dodecilsulfato de sódio (SDS) e para brometo, respectivamente, eletrodo indicador e de referência, para medidas potenciométricas. Os eletrodos foram utilizados em solução de SDS e em mistura de SDS e poli(oxietileno) (PEO). Os perfis de potencial da célula (E) versus a concentração de SDS, na ausência e em presença de 0,5% de PEO, são sensíveis ao processo de associação cooperativa entre SDS e PEO e indicativos de parâmetros como concentração crítica de agregação, cac, e concentração de saturação do polímero, psp. Os parâmetros obtidos por esta metodologia estão em concordância com os obtidos por técnicas clássicas como a de tensão superficial e a de condutividade elétrica.

Surfactant-selective electrodes to sodium dodecyl sulfate (SDS) monomer and bromide were constructed, respectively, electrode idicator and reference electrode. The electrodes were tested for solutions of SDS and in mixture of SDS and poly(ethylene oxide) (PEO). The profiles obtained measuring the potential (E) versus SDS concentration in the presence of 0.5% PEO are sensitive to polymer-surfactant parameters such as the onset of cooperative association of SDS to PEO, the critical aggregation concentration (cac), and the polymer saturation by SDS monomers (psp). The obtained parameters are in agreement with those values found by surface tension and electrical conductivity.

This work describes the construction of a home-made low-cost reactor, using easily available materials, capable of destroying efficiently dissolved organic matter. Just 30 minutes of irradiation were sufficient to destroy more than 99% of the humic acids present in a solution of 4 mg C L-1. Copper speciation was evaluated in natural waters of different salinities to test the reactor's efficiency in destroying organically complexed metal species. The effect of the organic matter concentration, salinity, dissolved oxygen and temperature in the photo-oxidation process is discussed.