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A sensor based in a graphite–polyurethane composite electrode modified with the mesoporous nanostructured silica with hexagonal array of pores called Santa Barbara Amorphous type material (SBA‐15) containing nickel was built. The presence of Ni, incorporated during the synthesis of SBA‐15, resulted in an increase in sensitivity when compared to the other electrodes based on the unmodified SBA‐15. A procedure was proposed for the determination of Cu2+ in ethanol biofuel by square wave stripping voltammetry with linear response in concentration levels of 1.0×10−8 and 1.0×10−7 mol L−1, resulting in a limit of detection of 1.83×10−10 mol L−1 and precision (RSD) of 2.09 %.

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Square-wave adsorptive stripping voltammetry (SWAdSV) was used to determine iron in ethanol and biodiesel using a bismuth-film electrode (BiFE) prepared onto the surface of a glassy carbon electrode (GCE) by electrochemical deposition to promote the reduction of Fe (III) previously complexed with 1-(2-pyridylazo)-2-naphthol (PAN) directly in the electrochemical cell. The supporting electrolyte was composed by mixture of acetate buffer (0.1 mol L À1 , pH 4.5) and ethanol (40/60% v/v) into which 500 mL of a 0.1 mmol L À1 stock solution of PAN was added as complexing agent. The Fe (III)-PAN complex presented a well-defined current peak at À0.7 V. For biodiesel, a treatment with tetramethylammonium hydroxide (TMAH) was proposed as an efficient mean to minimized matrix interferences. A limit of detection of 6.0 Â 10 À8 mol L À1 (0.06 mmol L À1 ) and limit of quantification of 2.0 Â 10 À7 mol L À1 (0.2 mmol L À1 ) were obtained for Fe(III). Under the optimized conditions, there were no significant interferences from Cu(II), Al(III), Mn(II), Cr(III), Cd(II), Zn(II) and Ni(II) and Pb(II) while Ni(II) interfered significantly. The analytical curves produced linear responses with equations I (mA) ¼ (-1.315 Â 10 À7 ± 5.158 Â 10 À8 ) þ (-0.238 ± 0.01) [Fe (III)] (mmol L À1 ), R 2 ¼ 0.992 and I (mA) ¼ (-6.836 Â 10 À7 ± 1.124 Â 10 À8 ) þ (-0.408 ± 0.013) [Fe (III)] (mmol L À1 ), R 2 ¼0.998 for pure ethanol and biodiesel, respectively. The method produced satisfactory results in quantifying original quantities of Fe(III) in fuel ethanol (5.65 ± 0.71 mmol L À1 ) and biodiesel (1.28 ± 0.25 mmol L À1 ) at a 95% confidence limit (n ¼ 3).

The electrochemical process involving primaquine was studied at a glassy carbon (GC) electrode modified with multi-walled carbon nanotubes (MWCNT). The GC/MWCNTs electrode promoted an intense oxidation peak for primaquine, improving signal when compared to the one observed using bare GC as electrode. Besides the increasing in active electrode area, the MWCNTs seemed to provide faster electron transfer. The linear analytical response for primaquine, in the concentration range from 0.1 to 5.0 μmol L−1, was achieved on a supporting electrolyte consisting of Britton-Robinson buffer (0.02 mol L−1; pH 7.00) and KCl (0.25 mol L−1). The quantitative assay using square-wave voltammetry was performed by successive additions of standard into the electrochemical cell, containing the sample, with instrumental limit of detection (LOD) of 7.3 μg L−1 (28 nmol L−1). A procedure involving liquid-liquid extraction and thin-layer chromatography provided selectivity and pre-concentration required for the determination of traces of primaquine in urine samples (LOD of the method of 146 ng L−1). Recoveries in urine samples were statistically similar to the one achieved by HPLC.

A series of triphenylamino (TPA)-chalcones and triphenylamino-β-arylchalcones, displaying either D-π-D or D-π-A architecture, were synthesized through aldol condensations and Heck reactions. The chalcone derivatives display intense absorption bands ranging from 389 to 432 nm and molar extinction coefficients of ca. 10 5 L mol-1 cm-1 corresponding to π-π* electronic transitions. The photoluminescence emissions are peaked between 470 and 563 nm with large Stokes shifts (80-131 nm), attributed to charge transfer in the excited state. The dyes present low fluorescence quantum yields, which is attributed to radiationless excited state deactivation related to aryl rings rotation. Spectroscopic and electrochemical methods were used to determine the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. Both optical and electrochemical properties of the TPA-chalcone derivatives are considerably affected by the substitution pattern of the chalcones aryl rings and also by the β-arylation of the olefin moiety.

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