Different methods have been applied to solve special problems of metal analysis. First, the solid samples of tool steels were analyzed by X-ray fluorescence. Alternatively, an on-line electrodissolution implemented in a flow injection system and conventional dissolution procedure for determination of W, Mo, V and Cr in tool steels by ICP-AES is described. The resulting analyte solutions were compared with conventional dissolution procedure and determination by ICP-AES. The electrolytic procedure presented a good performance characterized by a sample throughput of 164 determinations per hour. Results were in agreement with those obtained by conventional acid dissolution.

An on-line electrodissolution procedure implemented in a flow injection system for determination of copper, zinc and lead in brasses alloys by ICP-AES is described. Sample dissolution procedure was carried out by using a PTFE chamber and a DC power supply with constant current. Solid sample was attached to chamber as anode and a gold tubing coupled in the chamber was used as cathode. An electrolytic solution flowing through the gold tubing closed the electric circuit with sample, in order to provide condition for electric dissolution when the DC power supply was switched on. The best results were achieved by using a 1.5 mol l-1 nitric acid solution as electrolyte and a 2.5 A current intensity. The procedure presented a good performance characterized by a relative standard deviation better than < 5% (n=5) and a sample throughput of 180 determinations per hour for Cu, Zn and Pb. Results were in agreement with those obtained by conventional acid dissolution (99% confidence level).

Foram analisadas e comparadas neste trabalho, quanto às qualidades físico-químicas, amostras de água de 29 (vinte e nove) afluentes do rio Negro, A maioria das águas e muito pobre em sais dissolvidos, e por outro lado bastante ácida, sendo observado que. as substâncias coloridas exercem influencia sobre algum parâmetros químicos isto bem demonstrado pelos resultados de coeficiente, de correlação a 5%. Os rios da margem esquerda provenientes das, montanhas localizadas ao norte são mais férteis em substâncias nutritivas minerais. Já os da margem direita, que em sua maioria nascem em terras alagadiças e em campinas, são considerados extremamente pobres. De um modo geral, são as condições físico-químicas e biológicas que influenciam os resultados de nitrogênio. Discute-se também a hipótese da fertilização de pequenas áreas inundáveis que atualmente estão de formando no baixo rio Negro, bem como o aparecimento de macrófitas aquáticas.

Inthis paper, water samples from 29 (twenty nine) tributaries of the Rio Negro went analysed and compared according to their physico-chemical qualities. The majority of the tributaries were very poor in dissolved minerals and highly acidic. Significant relationship were found between the level of colored organic substances ans several chemical parameters. The left bank afluents, originating form the mountains in the North, had higher nutrient levels. While the right bank afluents which, in their majority, originates in the "terras alagadiças" (swampy lands) and in "campinas" (podzol soils), were considered extremely poor. In general, physical, chemical, and biological conditions affect the nitrogen values. The recent fertilization of flooded areas and the appearance of aquatic macrophytes in the Lower Negro are discussed.

As condições hidroquímicas da bacia do Rio Parauari-Maués-Açu, estão estudadas a partir da determinações do ph, cálcio, magnésio, sódio, potássio, ferro, cloretos, cobre, zinco e mangnês, nas diferentes épocas do ano. Para isso, foram realizadas quatro excursões e estabelecidos onze pontos de coletas de amostras de água, ao longo do rio principal e igarapés afluentes.As análises mostraram claramente flutuações sazonais no rio que constitui o eixo principal da bacia, o Parauari-Maués-Açu e em alguns de seus principais tributários, como os rios Nambi , Amanã e Urupadi. Essas flutuações estão estritamente relacionadas com os períodos de cheia, seca e intermediários, mostrando a importância dessa massa de água na movimentação de sais, ao longo da bacia.

The chemical characteristics of the Parauari-Maués-Açu River Basin were examined. Water samples were collected during four differente excursions at eleven points along the mainstrean and tributaries. Samples were analysed for ph, calcium, magmesium, sodium, potassium, iron, chloride, copper, zinc, and manganese.The results demonstrate a clear seasonal fluctuations in the Parauari-Maués-Açu and some of its principal tributaries. These fleuctuations are directly related to variations in the river hidrograph showing the importance of this water massa in the movement of solutes along the basin.

No presente trabalho foram determinados os teores residuais de SO2 em passas elaboradas com bananas tratadas com solução de metabisulfito de potássio a 2%, acondicionadas em alumínio,, celofane, polietileno e alumínio+polietileno ("combinado") e armazenadas de 15 a 105 dias à temperatura ambiente. A determinação de SO2 foi realizada com medida potenciométrica em eletrodo com separação de ar (em sistema de fluxo contínuo). Constatou-se que: a) o produto perde SO2 após processamento; b) o celofane proporciona, relativamente aos demais materiais testados, uma maior retenção de anidrido sulfuroso nas passas; c) os teores de SO2 encontrados nas passas de banana desde os 15 dias até os 105 dias de armazenamento não ultrapassam o limite estabelecido pela Comissão Nacional de Normas e Padrões para Alimentos.

In the present work residual SO2 in banana figs was determined after treatment with 2% potassium metabisulfite solution, packaging in aluminum foil, cellophane, polyetylene film or aluminum foil+polyetylene and stores from 15 to 105 days at room temperature. It is concluded that: a) the product loses SO2 after processing; b) the cellophane a continuous flow system. It is concluded that: a) the product loses SO2 after processing; b) the cellophane retains more SO2 in the banana figs, than aluminum foil or polyetylene film; c) the amounts of SO2 found in the banana figs at any time after 15 days of storage were below the limit established by the CNNPA (National Commission for Food Standards and Regulations).