Determinação de cálcio e magnésio em plantas, pelo método do EDTA

Abstract

The present work reports a study of the chelatometric method (by EDTA titration) for determining calcium and magnesium in plant materials. A preliminary study about the influence of severals íons (Fe³ +, PO4³ -, Al³ +, SO4² - and Mn2+) was performed. The presence of sulfate and aluminum did not cause interference in the method. Manganese (200 micrograms) interferes by causing the color of the indicator to fade. Iron interferes only up 1 mg in the determination of calcium and up to 500 micrograms in the determination of calcium plus magnesium. Phosphate interferes, giving lower results, because the end point comes to soon. The elimination of phosphate interference was necessary. This ion can be removed by precipitation as ferric phosphate adding ferric iron, acetate and ammonium hidroxide. In order to compare the chelatometric (based in the proposed technique) and permanganometric (for calcium) and colorimetric (for magnesium) methods, five replications of differentes plants materials were analysed by the methods. The data obtained allowed to conclude that technique proposed is good and the accuracy is satisfactory.