This work describes an electrochemical and quantum chemical investigation of the fipronil insecticide. Cyclic voltammetry (CV) and square wave voltammetry (SWV) experiments were performed over a graphite-polyurethane (GPU) composite electrode. The fipronil molecule presents an one-electron irreversible oxidation reaction. Profiting the SWV signal a square wave stripping voltammetry (SWSV) procedure to determine the fipronil molecule in a 0.10 mol L-1 Britton-Robinson buffer solution, pH 8.0 was developed with accumulation potential and time of 0.50 V and 120 s, respectively. The limits of detection and quantification were 0.80 and 2.67 μg L-1, respectively. Recovery tests were performed in three natural waters samples with values ranging from 99.67 to 101.37%. Quantum chemical studies showed that the nitrogen atom of the pyrazole group is the most probable oxidation site of the fipronil molecule.
We present studies involving metallic ions and the herbicide glyphosate. The metallic complexes of Cu(II), Zn(II), Mn(II), Ni(II), Cd(II), Pb(II), Cr(III), Fe(III), Co(III), ammonium, sodium, Ag(I), alkaline earth metals and of some lanthanides ions are described. The complexes are discussed in terms of their synthesis, identification, stability and structural properties, based on data from the current literature.
This work presents the electrochemical and quantum chemical studies of the oxidation of the tricyclic antidepressant amitriptyline (AM) employing a carbon-polyurethane composite electrode (GPU) in a 0.1 mol L-1 BR buffer. The electrochemical results showed that the oxidation of AM occurs irreversibly at potentials close to 830 mV with the loss of one electron and one proton and is controlled by reagent and product adsorption. According to the PM3 results, the atom C16 is the region of highest probability for the oxidation of AM since it has the largest charge variation.
The electroreduction of Dipyridamole (DIP) was studied in 0.10 mol L-1 phosphate buffer solution (pH 3.0) on a mercury coated platinum microelectrode (Hg-ME), employing cyclic, linear sweep voltammetry and polarography techniques. The similarity between Hg-ME voltammetric profile and the sigmoidal polarographic waves both with a diffusion limited current is showed. Experiments with a hanging mercury drop electrode (HMDE) were performed in parallel to confirm the results obtained with Hg-ME, which indicated that the reduction occurs in two irreversible steps involving two electrons and two protons each step. The limiting diffusion current, concerning the first step, allows estimating the diffusion coefficient for DIP as being equal to 2.04 x 10-5 cm² s-1.
A eletrorredução do Dipiridamol (DIP) foi estudada em solução tampão fosfato 0,10 mol L-1 (pH 3,0) em microeletrodo de platina coberto com mercúrio eletrodepositado (Hg-ME), empregando as técnicas de voltametria cíclica, de varredura linear e polarografia. A similaridade entre o perfil voltamétrico obtido com Hg-ME e as ondas polarográficas sigmoidais com correntes limitadas por difusão é demonstrada. Experimentos com eletrodo de gota pendente de mercúrio (HMDE) foram realizados em paralelo para confirmar os resultados obtidos com Hg-ME, os quais indicaram que a reação de redução ocorre em duas etapas irreversíveis com o consumo de dois elétrons e dois prótons por etapa. A corrente limite de difusão, referente à primeira etapa de redução, permitiu estimar o coeficiente de difusão do DIP como sendo igual a 2,04 x 10-5 cm² s-1.
The Potentiometric Stripping Analysis (PSA) is described with emphasis on ultramicroelectrode applications with a laboratory developed computer based instrumentation. The technique potentialities as compared with the voltammetric approach are pointed out based on the current literature. Some results of trace metals analysis including zinc, cadmium, lead and copper in vinegar and canned food samples are presented. The mainly advantage found in our laboratory was the technique capability to analyse natural samples with minimum matrix interference and the low level of noise found in our determinations.