Sensores potenciométricos, amperométricos e condutométricos são sensores eletroquímicos com imensa aplicação nas áreas de meio ambiente, indústria e análises clínicas. O presente trabalho apresenta uma revisão generalizada dos aspectos fundamentais, os desenvolvimento e a contribuição destes sensores na área de química analítica, e reporta alguns aspectos relevantes dos avanços na área de sensores eletroquímicos no Brasil.Potentiometric, amperometric and conductometric electrochemical sensors have found a number of interesting applications in the areas of environmental, industrial, and clinical analyses. This review presents a general overview of the three main types of electrochemical sensors, describing fundamental aspects, developments and their contribution to the area of analytical chemistry, relating relevant aspects of the development of electrochemical sensors in Brazil.

A nickel modified boron doped diamond (Ni-BDD) electrode and nickel foil electrode were used in the determination of methanol in alkaline solutions. The Ni-BDD electrode was electrodeposited from a 1 mM Ni(NO 3 ) 2 solution (pH 5), followed by repeat cycling in KOH. Subsequent analysis utilised the Ni(OH) 2 /NiOOH redox couple to electrocatalyse the oxidation of methanol. Methanol was determined to limits of 0.3 mM with a sensitivity of 110 nA/mM at the Ni-BDD electrode. The foil electrode was less sensitive achieving a limit of 1.6 mM and sensitivity of 27 nA/mM. SEM analysis of the electrodes found the Ni-BDD to be modified by a quasi-random microparticle array.

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We report the fabrication of a Ni nanoparticle modified BDD electrode and its application in the electrocatalysis of primary alcohol electrooxidation. Modification was achieved via electrodeposition from Ni(NO 3 ) 2 dissolved in sodium acetate solution (pH 5). Characterization of the Ni-modified BDD (Ni-BDD) was performed using ex situ atomic force microscopy (AFM) and high resolution scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Large nanoparticles of nickel were observed on the BDD surface ranging 5 to 690 nm in height and 0.18 mm À3 in volume, and an average number density of ca. 13 Â 10 6 nanoparticles cm À2was determined. The large range of sizes suggests progressive rather than instantaneous nucleation and growth. Electrocatalysis of ethanol and glycerol, was conducted in an alkaline medium using an unmodified BDD, Ni-BDD and a bulk Ni macro electrode. The Ni-BDD electrode gave the better electrocatalytic performance, with glycerol showing the greatest sensitivity. Linear calibration plots were obtained for the ethanol and glycerol additions over concentration ranges of 2.8 -28.0 mM and 23 -230 mM respectively. This gave an ethanol limit of detection of 1.7 mM and sensitivity of 0.31 mA/M, and the glycerol a limit of detection of 10.3 mM with a sensitivity of 35 mA/M.

A new, versatile, and simple method for quantitative analysis of zinc, copper, lead, and cadmium in fuel ethanol by anodic stripping voltammetry is described. These metals can be quantified by direct dissolution of fuel ethanol in water and subsequent voltammetric measurement after the accumulation step. A maximum limit of 20% ( v/ v) ethanol in water solution was obtained for voltammetric measurements without loss of sensitivity for metal species. Chemical and operational optimum conditions were analyzed in this study; the values obtained were pH 2.9, a 4.7-microm thickness mercury film, a 1,000-rpm rotation frequency of the working electrode, and a 600-s pre-concentration time. Voltammetric measurements were obtained using linear scan (LSV), differential pulse (DPV), and square wave (SWV) modes and detection limits were in the range 10(-9)-10(-8) mol L(-1) for these metal species. The proposed method was compared with a traditional analytical technique, flame atomic absorption spectrometry (FAAS), for quantification of these metal species in commercial fuel ethanol samples.

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The synthesis of the indolequinones 8 and 9 starting from methyl 4-(benzyloxy)-5-methoxy-indole-2-carboxylate (10) is described. The methoxy group in the indolequinones 1, 2, 4, 5, and 7-9 can be displaced by various nitrogen nucleophiles (ammonia, 2-methoxyethylamine, aziridine, 2-methylaziridine, pyrrolidine) in 22-88% yield. The resulting amino-substituted quinones, together with their methoxy precursors, were studied by cyclic voltammetry to determine their reduction potentials, which, in DMF solution, lie in the range -1.355 to -1.597 V (vs ferrocene). The cytotoxicity of the compounds towards aerobic and hypoxic mammalian cells was also determined; in general, under aerobic conditions, the cyclopropamitosenes are more toxic than the corresponding pyrrolo[1,2-a]indolequinones, which are in turn more toxic than the simple 1,2-dimethylindolequinones, with many of the compounds in each series showing greater toxicity toward hypoxic cells.

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