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A stripping method for the determination of xanthine in the presence of hypoxanthine at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation at the thin-film mercury electrode followed by a fast linear scan voltammetric measurement of the surface species. Optimum experimental conditions were found to be the use of 1.0 × 10(-3) mol L(-1) NaOH solution as supporting electrolyte, an accumulation potential of 0.00 V for xanthine and -0.50 V for hypoxanthine-copper, and a linear scan rate of 200 mV second(-1). The response of xanthine is linear over the concentration ranges of 20-140 ppb. For an accumulation time of 30 minutes, the detection limit was found to be 36 ppt (2.3 × 10(-10) mol L(-1)). Adequate conditions for measuring the xanthine in the presence of hypoxanthine, copper and other metals, uric acid, and other nitrogenated bases were also investigated. The utility of the method is demonstrated by the presence of xanthine associated with hypoxanthine, uric acid, nitrogenated bases, ATP, and ssDNA.

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This paper describes a stripping method for the determination of acyclovir at the submicromolar concentration level. This method is based on controlled adsorptive accumulation of acyclovir at thin-film mercury electrode, followed by a linear cyclic scan voltammetry measurement of the surface species. Optimal experimental conditions include a NaOH solution of 2.0 × 10(-3) mol L(-1) (supporting electrolyte), an accumulation potential of -0.40 V, and a scan rate of 100 mV s(-1). The response of acyclovir is linear over the concentration range 0.02 to 0.12 ppm. For an accumulation time of 4 minutes, the detection limit was found to be 0.42 ppb (1.0 × 10(-9) mol L(-1)). More convenient methods to measure the acyclovir in presence of the didanosine, efavirenz, nevirapine, nelfinavir, lamivudine, and zidovudine were also investigated. The utility of this method is demonstrated by the presence of acyclovir together with Adenosine triphosphate (ATP) or DNA.

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Introducción: en Cuba se editó la primera Norma Cubana de Contaminantes Microbiológicos en 1987, a partir de la cual se propuso una actualización por el Comité Técnico de Microbiología de los Alimentos No 61. Objetivos: analizar y proponer criterios microbiológicos para los muestreos de segunda y tercera clases en alimentos, que respondieran a las condiciones climáticas y ecológicas del país, y a la forma de preparación y consumo de los productos. Métodos: se procedió a establecer grupos de alimentos, parámetros microbiológicos, categoría en relación con el peligro sanitario, plan de muestreo y criterios microbiológicos, para lo que se tomó en cuenta la NC 38-02-07:1987, la base de datos de los resultados de los laboratorios nacionales de análisis de alimentos y la literatura científica. Resultados: se definieron 17 grupos de alimentos, para consumo humano o animal. Se incluyeron nuevos parßmetros microbiol¾gicos a controlar, se mantuvieron los que aparecían en la NC 38-02-07,1987 y se especificaron los que se evaluaban en vigilancia. Se clasificaron los productos en diez categorías de acuerdo con el riesgo que involucraban y se aplicaron planes de muestreo representativos, con el uso de n 5. Se establecieron los criterios microbiológicos. La interpretación de resultados se resumió en tres categorías: aceptable, medianamente aceptable y rechazable. Conclusiones: con la implementación de esta Norma se logró una mayor protección al consumidor y reducir al mínimo el riesgo del producto

Introduction: technical Committee on Food Microbiology No. 61 has proposed an update of the first Cuban Standard for Microbiological Contaminants, published in 1987. Objectives: analyze and propose microbiological criteria for second and third class food sampling which would reflect the country's climatic and ecological conditions, as well as the different forms of food preparation and consumption. Methods: food groups, microbiological parameters, health hazard categories, a sampling plan and microbiological criteria were established, based on Cuban standard NC 38-02-07:1987, the database of results obtained by national food analysis laboratories, and scientific bibliography. Results: seventeen human and animal food groups were defined. New microbiological parameters were included, those contained in standard NC 38-02-07:1987 were retained, and specifications were developed for surveillance parameters. Food products were classified into ten categories according to the risk involved, and representative sampling plans were applied based on n 5. The required microbiological criteria were established. Results were classified into three categories: acceptable, fairly acceptable and rejectable. Conclusions: with implementation of the standard, consumer protection was improved and product-related risks were reduced to a minimum

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This paper describes a stripping method for the determination of nevirapine at the submicromolar concentration levels. The method is based on controlled adsorptive accumulation of nevirapine at thin-film mercury electrode, followed by a linear cyclic scan voltammetry measurement of the surface species. Optimal experimental conditions include a 2.0 x 10(-3) mol L(-1) NaOH solution (supporting electrolyte), an accumulation potential of -0.20 V, and a scan rate of 100 mV s(-1). The response of nevirapine is linear over the concentration range 0.01-0.14 ppm. For an accumulation time of 6 minutes, the detection limit was found to be 0.87 ppb (3.0 x 10(-9) mol L(-1)). More convenient methods to measure the nevirapine in presence of the efavirenz, acyclovir, didanosine, indinavir, nelfinavir, saquinavir, lamivudine, zidovudine and metals ions were also investigated. The utility of this method is demonstrated by the presence of nevirapine together with ATP or DNA.

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RESUMO

The cathodic adsorptive electrochemical behavior of guanine in the presence of some metal ions at the static mercury drop electrode was investigated. A 1.0x10(-3) mol l(-1) NaOH or a 2.0x10(-2) mol l(-1) Hepes buffer at pH 8.0 solutions were used as supporting electrolytes. The reduction peak potential for guanine was found to be around -0.15 V, which is very close to the mercury reduction wave. A new peak appears at -0.60 V in the presence of copper or at -1.05 V in the presence of zinc. A square wave voltammetric procedure for electroanalytical determination of guanine in 2.0x10(-2) mol l(-1) Hepes buffer at pH 8.0 containing 1.6x10(-5) mol l(-1)of copper ions, was developed. An accumulation potential of -0.15 V during 270 s for the prior adsorption of guanine at the electrode surface was used. The response of the system was found to be linear in the range of guanine concentration from 6.62x10(-8) to 1.32x10(-7) mol l(-1) and the detection limit was 7.0x10(-9) mol l(-1). The influence of DNA bases such as adenine, cytosine and thymine was also examined. Cyclic voltammetry was used to characterize the interfacial and redox mechanism.

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Se analizan los resultados de 3 849 muestras de queso estudiadas durante el período 1985-1988 en los Centros Provinciales de Higiene y Epidemiología. Los valores encontrados están entre 1 y 1,7 %. Se valoran los factores que pueden incidir en la contaminación de este alimento. Se proponen medidas de control

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Se presentan los resultados de 17 904 muestras de embutidos y ahumados, así como 7 209 muestras de productos cárnicos semielaborados sometidos a examen para la determinación de Salmonella. Se hace una valoración sanitaria de los resultados y se hacen consideraciones en relación con los factores que pueden haber incidido en los mayores aislamientos

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Se analizaron 1 177 muestras de ostiones para la determinación de Salmonella en 7 Centros Provinciales de Higiene y Epidemiología. Se obtuvieron valores promedio en el período que oscilaron desde 0 % de aislamiento en el año 1985 hasta el 4,7 % en el año 1987. Por provincias varió del 0 % en Granma al 10,7 % en Matanzas durante los años 1985-1988. Se valoraron los resultados y posibles causas de la contaminación. Se establecen conclusiones para mejorar la calidad del producto

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Se analizan 3 745 muestras para determinar la presencia de Salmonella en 6 Centros Provinciales de Higiene y Epidemiología en Pinar del Río, La Habana, Matanzas, Holguín, Granma y Santiago de Cuba. Se detectan valores superiores a otras provincias en Matanzas y La Habana. Se analizan los factores de contaminación y se sugieren medidas para evitar la misma en este producto

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