Determinação catalítica de molibdênio(vi) em tecidos vegetais empregando detecção espectrofotométrica

Abstract

A procedure for espectrophotometric determination of molybdenum in plants tissues was developed, using a catalytic oxidation of iodide by hydrogen peroxide in acid médium. In good conditions of work, a procedure used suggest aqueous Solutions of the H2SO4, Kl and H2O2 in concentrations of 0,010, 0,0060 and 0,0020 moldm'3, respectively. The reaction must be performed in a separatory funnel and, after ten minutes of reaction, the reaction product is iodine, wich is extracted adding 3,0x10‘3 dm3 of metyl-isobutyl-ketone. The analytical signal is the difference between the absorbance obtained for catalysed reaction using molybdenum and the reaction uncatalysed. Individuais absorbance are obtained at 360 nm using a cuvette of 10 mm. The effects of the interferents (Fe, Ti, W, Cr, V and PO43"), are minimized by means of the extraction of molybdenum with a-benzoinoxime, followed by previous treatment of sample. The analytical calibration curve is linear from 10,0 to 60,0 pg.dm'3 and is represented by AAbs = 0,0085CMo - 0,011, with r2 = 0,9918. The relative standard deviation varies in a range of 18,1 - 4,35%, in a concentration internai of 10,0 and 50,0 pg.dm'3, respectively (started of 12 experiments were performed). The limit detection calculated presents a standard deviation of 1,7 pg.dm'3, (started of 12 experiments were performed ofreagent blank). The precision and accuracy of the proposed metodology was estimated comparing a different method used for determination of the molybdenum in beans leaves Faseolus Vulgaris. Dithiol Colorimetric Methods is used as a standard method for comparision. The results were checked apply “F” and “t” statistic tests, wich shown that both methods present good results in a perfect agreement.