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This work describes the electroanalytical determination of Chlorpyriphos pesticide in natural waters using hanging mercury drop electrode allied to square wave adsorptive cathodic stripping voltammetry. The best responses were obtained in Britton-Robinson buffer solutions at pH 2.0, using a frequency of 100 [s.sup.-1], a scan increment of 5 mV, a square wave amplitude of 25 mV and an accumulation potential of -0.4 V during 60 s. Therefore, voltammetric responses showed the presence of one well-defined and irreversible reduction peak, at -1.08 V vs. Ag/AgCl/KCl 1.0 M, which involves two electrons in the reduction of carbon-nitrogen bond in the N-heterocyclic system with the participation of protonation equilibrium preceding the electron transfer reaction. Analytical curves were constructed and compared to similar curves performed by gas chromatograph coupled to a selective nitrogen-phosphorus detector, which demonstrates that the proposed methodology is suitable for determining contamination by Chlorpyriphos in complex samples. Keywords: Chlorpyriphos, organophosphorous pesticide, natural water, adsorptive square wave voltammetry, hanging mercury drop electrode, The Ceara State in Brazil is located in a semi-arid climate region that promotes irrigated agriculture to become the third largest producer and exporter of tropical fruits (melon, pineapple, papaya, [...]

The electrochemical behaviour and analytical detection procedure for nimesulide (NIM) and ofloxacin (OFX) and their assay in commercial formulations were evaluated using square-wave voltammetry (SWV) combined with a hanging mercury drop electrode (HMDE). All experimental and voltammetric conditions were previously optimized to obtain the best analytical signal in terms of intensities and profile of the reduction peaks. For NIM, the peak currents were related to the one-electron reduction of a nitro group to a stable radical anion, which is followed by a one-electron transfer and a protonation step with a consequent formation of a nitrosoanion. The voltammetric results indicated that the mechanism of OFX involved the transfer of two electrons and two protons in a totally irreversible reduction related to the conversion of a ketone group to an alcohol group. Analytical parameters such as linearity range, equations of the analytical curves, correlation coefficients, detection and quantification limits, recovery efficiency, and relative standard deviation for repeatability and reproducibility experiments were compared to similar results obtained by the use of UV-Vis spectrophotometry, and the results showed that the voltammetric procedure using HMDE is suitable to determine pharmaceutical compounds in complex samples. The applicability of the proposed procedure was tested on pharmaceutical formulations of NIM and OFX by observing the stability, specificity, recovery and precision of the procedure in tablets, oral solution and ophthalmic solution. Keywords: nimesulide, ofloxacin, square-wave voltammetry, pharmaceutical formulations, electrochemical behaviour DOI: 10.1134/S1061934814010079, The arrival of a great number of generic drugs, and, in particular, the appearance of various pharmaceutical laboratories, which are responsible for the research, production, distribution and commercialization of pharmaceutical [...]