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This article in SSSAJ

  1. Vol. 32 No. 1, p. 48-51
    Received: June 22, 1967
    Accepted: Sept 14, 1967

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An Acid-Free Vanadate-Molybdate Reagent for the Determination of Total Phosphorus in Soils1

  1. H. L. S. Tandon,
  2. M. P. Cescas and
  3. E. H. Tyner2



An acid-free vanadate-molybdate reagent was developed for the spectrophotometric determination of P in HClO4 digests of soils. The optimum acidity in the analysis is derived from the residual acidity of the HClO4 digest of soils. A comparative study of the proposed reagent with a commonly used molybdenum-blue method on ten widely different soils indicated that the proposed method gave highly reproducible results and was not affected by high amounts of Fe3+ which is invariably present in soils. In rare cases chromium interference can be serious because of the similarity of the color of the chromate ion to that of the molybdivanadophosphoric complex. For soils low in chromium, chromate interference can be removed by volatilization as chromyl chloride during the digestion. The modified reagent greatly simplifies the determination of total P and is admirably suited for automated analysis.

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