A determinação do boro em plantas pelo método colorimétrico da curcumina

Abstract

The determination of boron in vegetables by the curcumin colorimetric method is based on the formation of the rosocianin complex in acetic-sulphuric media. In this procedure the reaction takes place in solution at room temperature, needing not to control the temperature at 55 3°C, as with the common method in which the rubrocurcumin complex is formed. An aliquot of the vegetable extract is rendered alkiline by adding a solution of NaOH and then dried over a vapor bath. To the residue is added a 0,125% curcumin acetic solution and a (1 + 1) acetic-sulphuric solution. The reaction is completed in 15 minutes. In the application of the method to plant materials analysis, several aspects were studied: interferents and their elimination, the recovery of boron from the ashed samples, the contamination due to filtration through paper filter, and the precision and accuracy of the method. Among the normally found elements in vegetable aske, the one interfering were: Ca2+, Mg2+, Fe3+, Mn2+ and Co2+. They were separated by passing the extract through cation exchange resin. The method, as described, may be considered efficient for the boron determination in vegetables, since it showed good precision and accuracy, coupled with high sensitivity, allowing the determination of as low as 2 ppm of boron in vegetables, within the limits of the least erros.