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O presente trabalho mostra a modificação da superfície de eletrodos de grafite pelos compostos 8-hidroxiquinoleina (8-HQ) e ácido 8-hidroxiquinoleina 5-sulfônico (8-HQS). Voltametria cíclica foi usada para caracterizar o comportamento da superfície. A superfície modificada exibiu uma afinidade para complexar Cu(II) presente na solução, formando um complexo na superfície o qual foi empregado para análise de Cu(II) em nível de traços. Dos metais Zn, Ni, Pb, Co e Cd, nenhum apresentou interferência até um excesso de concentração de 10 vezes. Significante interferência foi observada para os íons Co(II), Cd(II) e Fe(II), para um excesso de concentração de 100 vezes sobre o analito. Voltametria no modo pulso diferencial, combinada com um processo de pré-concentração-redissolução e o método de adição padrão foram usados para as medidas analíticas. Um limite de detecção de 5,1×10 -9 mol L -1 foi obtido na determinação de cobre em água.Surface modification by 8-hydroxyquinoline-5-sulfonic acid (8-HQS) or 8-hydroxyquinoline (8-HQ) on a graphite electrode through irreversible adsorption is reported in this paper. Cyclic voltammetry was used to characterize the surface behavior. The modified surface exhibited an affinity to chelating Cu(II) in the solution, forming a Cu(II) complex, which was employed for Cu(II) trace analysis. Of the metals Zn, Ni, Pb, Co, and Cd, none presented interference until excess concentration of 10 times. Significant interference could be observed from Co(II), Cd(II) and Fe(II) for an excess concentration of 100 times on the analyte. A differential pulse voltammetry, combined with a preconcentrating-stripping process and a standard addition method was used for the analysis. A detection limit for trace copper determination in water, such as 5.1×10 -9 mol L -1 , was obtained.Keywords: 8-hydroxyquinoline-5-sulfonic acid, 8-hydroxyquinoline, surface complex, stripping voltammetry, trace copper determination IntroductionIn recent years, applications of chemically modified electrodes (CME) have made great success in various areas of research and development, such as material corrosion and inhibition, electrocatalysis, electronics, biosensors and electroanalysis. [1][2][3][4][5][6][7][8] In the analysis of trace metals, CME have shown some advantages over other analytical methods and have been employed as powerful tools for concentration determination and surface structure identification. 9,10 One of the strategies for surface modification is to employ organic ligands such as phenanthrolines, [11][12][13][14] anthraquinone, 15 pyrazine, 16 alizarin, 17,18 and triazine 19 which adsorb irreversibly onto the surface of a glassy carbon electrode. Generally, these molecules contain a large conjugated benzene rings that can be easily and irreversibly attached on the carbon or graphite material electrode surface, forming the CME.8-hydroxyquinoline-5-sulfonic acid (8-HQS) and 8-hydroxyquinoline (8-HQ) as shown in Figure 1 have been identified as effective reactants for chemical extraction and metal ion determ...

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An automatic procedure for the determination of ethanol in wines using a flow system based on multicommutation and enzymatic reaction is described. Alcohol oxidase was immobilized on aminopropyl glass beads and packed in an acrylic column. The peroxide due to enzymatic reaction with ethanol reacted with luminol and generated the chemiluminescence radiation that was monitored by using a laboratory-made detector based on photodiodes. The system manifold comprised a set of 3-way solenoid valves controlled by a microcomputer furnished with electronic interfaces, which ran on software written in Quick BASIC 4.5 to provide facilities to perform on-line sample dilution, reagent addition, and data acquisition. After system parameters optimization, ethanol samples were processed without prior pretreatment. The following suitable features were achieved: linear response ranging from 2.5 to 25% (v/v) ethanol, relative standard deviation of 1.8% (n = 10), detection limit of 0.3% (v/v) ethanol, sampling rate of 23 determinations per hour, and low reagent consumption of 0.23 mg luminol and 7 mg hexacyanoferrate (III) per determination. When the results were compared with those obtained using the AOAC Official Method, no significant difference at the 90% confidence level was observed.