Determinação colorimétrica do silício em vegetais

Portuguese. O presente trabalho relata os estudos do método colorimétrico de determinação do silício, baseado na reação do citado elemento com o anion molibdato e posterior redução do sílico-molibdato formado com solução de ácido ascórbico contendo ferro divalente. Os estudos efetuados permitiram estabelecer uma técnica rápida para determinação do silício em material vegetal, mediante ataque das cinzas provenientes do material vegetal, com ácidos clorídrico, fluorídrico e excesso de ácido bórico, e posterior aplicação do método colorimétrico. Foram realizadas determinações de silício em materiais vegetais de diferentes origens, obtendo-se satisfatória precisão e os resultados concordaram razoavelmente com aqueles fornecidos pelo método gravimétrico tradicional.

English. The present work reports a study about the determination of silicon in plant materials, using the method based in the formation of heteropoly blue complex (molybdenum blue method) A preliminary study about the influence of several factors that may affect the method was performed. It was studied the absorption of the molybdenum blue, the influence of oxalic acid, effect of time and pH on the formation of molybdsilicic acid and its reduction, the influence of the use of hydrofluoric acid for solubilization of silicates and the reducing solutions. Based in this preliminary studies, it was proposed a technique for the determination of silicon in plant materials employing the colorimetric method. In the recommended procedures the plant materials ash is treated with a mineral acid (HC1), hydrofluoric acid and excess of boric acid. The reduction of molybdisilicic acid is made using an acid ascorbic solution containing divalent iron. In all procedure it is not necessary the use of platinum or nickel ware. In order to compare the colorimetric (based in the proposed technique) and gravimetric methods, five replications of differents plant materials were analysed by both methods. The data obtained allowed to conclude that the technique proposed is good and the accuracy is satisfactory.