A determinação espectrofotométrica do cobalto pelo método da 2,2'-dipiridil cetoxima (I) - estudos sobre o reativo, pH e tampão

The initial studies are presented, relative to the experimental part of the method of the 2,2'-dypiridyl ketoxime, for determination of cobalt. The preparation technique of the reagent from the corresponding ketone was presented. The use of 1.0 ml of the 1% reagent solution in 80% ethyl alcohol was suggested, for the determination of up to 10 micrograms of cobalt. The above solution was tested until 90 days after it's preparation, and no alteration was detected. The best pH conditions, for the formation and extration of the colored compound is between 7.0 and 8.0. Among several buffer solutions used, the most efficient was the one prepared with sodium citrate 1 molar, triethanolamina (1+2), in the proportion of 2:1, after ascertaining the pH at 7,8 with 30% citric acid. Studies about solvents, effects of several ions and the application of the method to plant analysis, will be presented later.No presente trabalho foi desenvolvida a primeira fase dos estudos experimentais do método da 2,2'-dipiridil cetoxima, para a determinação do cobalto. Os ensaios foram conduzidos em soluções puras e dentre os aspectos estudados constam; o reativo, preparo, concentração e conservação; o pH, influencia sobre a formação e extração do composto colorido; o sistema tampão, influencia sobre a reação, eficiência e escolha. Numa seqüência, serão apresentados posteriormente estudos sobre solventes, influência de diversos ions e aplicação do método em análises de plantas