Determinação do zinco em vegetais pelo método do zincon

Abstract

This paper deals with the separation of zinc from other elements by means of anion exchange resin (Merck, III) and its colorimetric determination using zincon reagent, in plants. Some factors influiencing the method were studied such as: 1 - zinc-zincon complex stability; 2 - pH influence on the complex formation; 3 - interval of hydrocloric concentration for best absorption of zinc by the resin; 4 - effect of KC1 and NaNO3 solution volumes on the absorption and elution of zinc in the column; 5 - interference by other ions, specially those associated with zinc in vegetables; 6 - accuracy and precision of the zincon method; 7 - comparison of zinc estraction from the plant tissue by dry and wet ashing and fluorization, etc. The reagent is very stable but the color complex should be red within 30 minutes wheter developed in the light or in the dark. The volumes and concentration of reagents recomended by JOHNSON & ULRICH are good. Zinc is best absorbed by the resin in hidrocloric solution circa 2 normal. Other ions, usually found in plant analyses, in amounts from 10 to 100 or 500 micrograms did not interfer with 20 microgram of zinc. By comparison, repetition and recuperation it was observed that the present method is fairly accurate and well precise. Dry ashing gave results as good as the other 2 procedures; there was no statistical diference among them at the level of 5 %. The method may have no great accuracy for general application but is good enough for plant analysis.