Determinação catalitica de molibdenio em plantas, usando analise em fluxo continuo monossegmentado com detecção espectrofotometrica

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

A procedure has been developed for the spectrophotometric determination of molybdenum in plants using the Continuous Monosegmented Flow Analysis technique with catalytic oxidation of I by H2O2 in acid medium. The analytical signal, the difference between the absorbance resulting from the Mo(VI) catalyzed reaction and the non-catalyzed reaction, was optimized using multivariate and univariate procedures. Under optimum conditions, the system operates with the reagents KI, H2SO4 and H2O2 in concentrations of 0.1528 M, 0.0665 M and 0.0041 M, respectively, within a precision of 0.0005 M. These reagents were pumped at 1.2 ml min. The flow rate of the sample was fixed at 4.7 ml min, the sample volume at 300 ml, the reaction time at 130 s, the system temperature at ( 25±2 )°C and the injection frequency at 72 h . Under these conditions were studied the interferences of Fe(III), Ti(IV), W(VI), Cr(VI), V(V), which are also catalizers for this reaction, as well as phosphate and the ionic stregth. It was observed that only Ti(IV) does not interfere. It was thus decided to incorporate a prior separation of Mo(VI) from interferring species by means of reaction with a-benzoinoxime and extraction in to choroform. The calibration curve obtained after submitting the standards to the extraction procedure is linear to 50 ng ml and is described by the equation: DA = 0.007 + 0.014 CMo. The limit of detection found was 1.0 ng ml and the relative standard deviation was less than 1.5% over the entire linear range. The accuracy or the method was evaluated by means or plant samples supplied by the "International Plant-analytical Exchange" (IPE), from the Wageningen Agricultural University, The Netherlands. By direct comparison, all of the results obtained for the determiation of Mo(VI) in these samples were acceptable by the recommended IPE criteria.

ASSUNTO(S)

molibdenio - analise espectral molibdenio - agricultura

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