Arsenic and germanium determination by hydride generation in the D.C. plasma optical emission spectrometer

Modifications to the commercial hydride generator, manufactured by Spectrametrics, resulted in improved operating procedure and enhancement of the arsenic and germanium signals. Experiments with arsenic(III) and arsenic(V) showed that identical reiults could be produced from both oxidation states. However, since arsenic(V) is reduced more slowly than arsenic(III), peak areas and not peak heights must be measured when the arsine is immediately stripped from the system (approximately 5 seconds reaction). When the reduction is allowed to proceed for 20 seconds before the arsine is stripped, peak heights may be used. For a 200 ng/mL solution, the relative standard deviation is 2.8% for As(III) and 3.8% for As(V). The detection limit for arsenic using the modified system is 0.50 ng/mL. Studies performed on As(V) standards show that the interferences from 1000 mg/L of nickel(II), cobalt(II), iron(III), copper(II), cadmium(II), and zinc(II) can be eliminated with the aid of 5 M Hel and 3% L-cystine. Conditions for the reduction of germanium to the corresponding hydride were investigated. The effect of different concentrations of HCl on the reduction of germanium to the covalent hydride in aqueous media by means of NaBH 4 solutions was assessed. Results show that the best response is accomplished at a pH of 1.7. The use of buffer solutions was similarly characterized. In both cases, results showed that the element is best reduced when the final pH of the solution after reaction is almost neutral. In addition, a more sensitive method, which includes the use of (NH4)2S208' has been developed. A 20% increase in the germanium signal is registered when compared to the signal achieved with Hel alone. Moreover, under these conditions, reduction of germanium could be accomplished, even when the solution's pH is neutral. For a 100 ng/mL germanium standard the rsd is 3%. The detection limit for germanium in 0.05 M Hel medium (pH 1.7) is 0.10 ng/mL and 0.09 ng/mL when ammonium persulphate is used in conjunction with Hel. Interferences from 1000 mg/L of iron(III), copper(II), cobalt(II), nickel(II), cadmium(II), lead(II), mercury(II), aluminum(III), tin(IV), arsenic(III), arsenic(V) and zinc(II) were studied and characterized. In this regard, the use of (NH4)ZS20S and Hel at a pH of 1.7 proved to be a successful mixture in the sbppression of the interferences caused by iron, copper, aluminum, tin, lead, and arsenic. The method was applied to the determination of germanium in cherts and iron ores. In addition, experiments with tin(IV) showed that a 15% increase in the tin signal can be accomplished in the presence of 1 mL of (NH4)2S20S 10% (m/V).

Blueprint - 200 K.W. D.C. Vert. Type Gen. 125 V. 8 P. 600 R.P.M., B 89521, 10586, 2-R1-H21.6

A blueprint produced by Westinghouse Electric & MFG. Co. in Pittsburgh, Pennsylvanna. The blueprint is dated 19 August 1903 and is stamped "OBSOLETE".

Estudio Estratégico Sectorial aplicado en cinco Hospitales Universitarios IV Nivel de complejidad en la ciudad de Bogotá D.C.

El estudio estratégico sectorial desarrollado en cinco Hospitales Universitarios de la ciudad de Bogotá D.C., presenta como objetivo general, la aplicación de la metodología de análisis estructural de sectores estratégicos con el propósito de conocer el nivel de hacinamiento del sector, las oportunidades para su desarrollo, el análisis de las fuerzas de mercado y el nivel de atractividad sectorial. El estudio concluye que la tendencia del sector se encuentra hacia la presencia de equilibrio competitivo y la no existencia de factores diferenciadores entre las organizaciones estudiadas. El análisis sectorial detecta la necesidad de crear oportunidades de desarrollo que permitan a las organizaciones salir de los procesos de imitación en los cuales están inmersos. Finalmente, se resalta la necesidad de fortalecer las relaciones y alianzas entre los competidores, proveedores y compradores.

A controvérsia nestoriana e suas implicações político-administrativas nas cartas de Cirilo de Alexandria (séc. V d.c.)

Pós-graduação em História - FCHS

Sofistas e filósofos na administração imperial: o olhar de Eunápio sobre a unidade política do império Romano no século IV D. C

Pós-graduação em História - FCHS

A mulher na visão de Tertuliano, Jerônimo e Agostinho séc. II - V d.c

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Oneirokritika de Artemidouro de Daldis (séc. II D. C.): livros de análise de sonhos - livro V

Pós-graduação em Linguística e Língua Portuguesa - FCLAR

Juan Antonio López Férez (Ed.) Desde los poemas homéricos hasta la prosa griega del siglo IV d. C., Madrid, Ediciones Clásicas, 1999, VIII + 523 pp.

Fil: Chazarreta, Daniela Evangelina. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Juan Antonio López Férez (Ed.) Desde los poemas homéricos hasta la prosa griega del siglo IV d. C., Madrid, Ediciones Clásicas, 1999, VIII + 523 pp.

Fil: Chazarreta, Daniela Evangelina. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.