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Um eletrodo íon seletivo foi construído e avaliado para determinação de íons amônio em águas naturais. O eletrodo consiste de uma pasta de carbono com o compósito SiO 2 /ZrO 2 / fosfato-NH 4 + obtido pelo processo de sol-gel. O eletrodo exibe uma resposta sub-Nenstiana para concentrações entre 7,7×10-7 e 4,0×10 -2 mol L -1 e um limite de detecção de 1,58×10 -7 mol L -1 (8,5×10 -3 ppm). A resposta do eletrodo foi rápida (1 minuto). Os coeficientes de seletividade K pot A,B para os diversos íons geralmente presentes em águas naturais foram determinados pela aplicação do matched potential method. O método potenciométrico com o eletrodo íon seletivo foi validado pelo método de Berthelot (método padrão) pela determinação de íons amônio em águas naturais. O eletrodo íon seletivo provou ser satisfatório para o controle de qualidade de águas naturais.Ion selective-electrode was constructed and evaluated for determination of ammonium ions in natural waters. The electrode consists of paste carbon with the composite SiO 2 /ZrO 2 /phosphate-NH 4 + obtained through sol-gel process. The electrode exhibits a sub-Nernstian response for ammonium concentrations between 7.7×10 -7 and 4.0×10 -2 mol L -1 and a detection limit of 1.58×10 -7 mol L -1 (8.5×10 -3 ppm). The electrode response for ammonium was fast (1 minute). The selectivity coefficients K pot A,Bfor several ions usually present in natural waters were determined applying the matched potential method. The potentiometric method with the ion selective electrode was validated by the Berthelot method (standard method), through the determination of ammonium ions in natural waters. The ion selective-electrode proved suitable for routine quality control of natural waters by potentiometry.Keywords: ammonium ion sensor, potentiometric sensor, natural waters IntroductionThe presence of ammonium ions in rivers and lakes can be associated in most cases to pollution caused by livestock, intensive agriculture and mainly, nowadays, to liberation of domestic sewage in courses of superficial waters in an indiscriminate way and in larger and larger amounts.Ammonium ion sensor is a useful tool in environmental pollution control, 1 food and clinical analysis 2-4 and other industrial applications.5 Among the ion sensors, ammonium sensor is also used more frequently as potentiometric biosensor in which enzymes or microbial cells are immobilized on the surface of the sensor. 6,7 Due to the many applications of the ammonium ion sensors, design of solid-state sensor for ammonium and its fabrication through simple procedure are desirable. 8Inorganic ion exchangers are characterized by high thermal stability and resistivity towards strong oxidizing agents and mineral acids. Recently the SiO 2 /ZrO 2 / phosphate composite was prepared by the sol-gel process, 9 which allies the good properties of ionic exchange of the zirconium(IV) phosphate 10,11 in a matrix of mixed oxide, SiO 2 /ZrO 2 high and homogeneously dispersed. This composite presents high superficial area, phosphate groups on the surface o...

Um novo polímero, cloreto de 3-n-propilpiridínio-silsesquioxano (SiPy + Cl -), foi utilizado na preparação de um eletrodo. Este eletrodo íon seletivo, formado de um bastão de grafite recoberto pelo polímero, foi construído e avaliado pela determinação de Cr(VI) em amostras de águas residuárias de indústrias de galvanoplastia e de couro. O eletrodo exibiu uma resposta Nernstiana para Cr(VI) entre as concentrações 3,1×10-6 e 1,8×10 -2 mol L -1 e limite de detecção de 2,8×10-6 mol L -1 (0,15 ppm). A resposta do eletrodo para Cr(VI) foi rápida (15 s) e o potencial independente do pH na faixa de 3,0 a 7,0. Os coeficientes de seletividade para diversos ânions mostram que o eletrodo apresenta um excelente desempenho. O sensor exibe um tempo de vida útil de 6 meses com boa reprodutibilidade. A determinação de Cr(VI) em águas residuárias de indústrias de galvanoplastia e de couro usando o sensor foi realizada com sucesso.A new polymer, silsesquioxane 3-n-propylpyridinium chloride (SiPy + Cl -), was used in the preparation of an electrode. The polymer coated graphite rod ion selective electrode for Cr(VI) was constructed and evaluated for the determination of Cr(VI) in samples of electroplating and leather industry wastes. This electrode exhibited a Nernstian response for Cr(VI) concentrations between 3.1×10 -6 and 1.8×10 -2 mol L -1 and a detection limit of 2.8×10 -6 mol L -1 (0.15 ppm). The response of the electrode for Cr(VI) was fast (15 s) and the independent potential of pH in the range of 3.0 to 7.0. The selectivity coefficients for several anions showed that the electrode presents excellent performance. The sensor exhibits a shelf-life of 6 months with good reproducibility. Determination of Cr(VI) in electroplating and leather wastes using the sensor was successfully achieved.

Uma superfície de grafite bem polida foi recoberta com um filme fino do polímero cloreto de n-propilpiridínio silsesquioxano. Sobre o filme do polímero fortemente aderido ao grafite, a espécie eletroativa [Fe(CN) 6 ] 4-foi adsorvida por meio de uma reação de troca iônica. O eletrodo resultante, (graph/SiPy + ) 4 [Fe(CN) 6 ] 4-(graph = grafite e SiPy + representa o polímero N-propilpiridinio silsesquioxano), mostrou-se quimicamente muito estável e foi utilizado para oxidar eletrocataliticamente o ácido ascórbico em solução de KCl 0,1 mol dm -3 , em pH entre 4,5 e 6,5. O eletrodo foi utilizado para determinar vitamina C em tabletes e em sucos de laranja processados. Os resultados mostraram uma boa concordância com aqueles obtidos utilizando o método padrão de titulação com 2,6-diclorofenolindofenol.A well polished graphite surface was coated with a thin film of N-propylpyridinium chloride silsesquioxane polymer. On to the strongly graphite-adhered polymer film the electroactive species [Fe(CN) 6 ] 4-was adsorbed by means of an ion exchange reaction. The resulting electrode (graph/ SiPy + ) 4 [Fe(CN) 6 ] 4-(graph = graphite and SiPy + represents the N-propilpyridinium silsesquioxane polymer) was chemically very stable and was used to electrocatalytically oxidize ascorbic acid in solution (pH between 4.5-6.5) in 0.1 mol dm -3 KCl. The electrode was used to determine vitamin C in tablets and in processed orange juices. The results were in accord with those obtained by using the standard 2,6-dichlorophenolindophenol titration method.

A new material of cotton fiber/Al 2 O 3 / SiPy þ Cl À , COTALPy, was prepared containing on its surface the polymer silsesquioxane 3-n-propylpyridinium chloride strongly adhered. This new composite based on long fibers of natural cotton is chemically stable and had its adsorption properties studied. The COTALPy presented a maximum ionic exchange capacity of 0.85 mmol g À1 by potentiometric titulation. The adsorption isotherms of CuCl 2 , ZnCl 2 , CdCl 2 , NiCl 2 , and FeCl 2 in ethanol solutions were determined for each metal. The adsorption process was studied and data compared with the Langmuir model. The maximum adsorption capacities (in mmol g