Determination of molybdenum in soil test extracts with potassium iodide plus hydrogen peroxide reaction
2000
Fontes, R.L.F. | Dallpai, D.L. | Braga, J.M. | Alvarez V, V.H.
The potassium iodide and hydrogen peroxide reaction (KI+H2O2) is catalyzed by molybdate. Our objective was to use this reaction to determine molybdenum (Mo) in Mehlich 1 (1:10) soil test extracts. A 350-nm wavelength and 10-minute reaction time were selected for the determination and absorbance was linear for 0.0 to 0.15 mg L(-1) Mo. Ten samples of a LEd-Iturama soil were extracted with Mehlich 1 and Mo determined. These extracts were also mixed and Mo determined on 10 aliquots of the mixture. Molybdenum concentration in the soil had a coefficient of variation (CV) of 23.5%, whereas that for the mixture was 3.95%. The low CV for the mixture indicates good precision for this method. The higher CV for the individual extracts indicates that most of the variation comes from the extraction phase of individual samples. To show the practical utility of the method, Mo maximum adsorption capacities (MoMAC) of 16 soils, primarily Oxisols, from Minas Gerais, Brazil were determined. The MoMAC varied from 0.15 to 2.02 mg g(-1) and there were good correlations between MoMAC and soil clay content as well as between MoMAC and soil organic carbon content. From our experience, use of the KI+H2O2 reaction is a practical method of determining Mo in Mehlich 1 soil test extracts.
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