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This article in AJ

  1. Vol. 64 No. 3, p. 398-401
     
    Received: Oct 22, 1971


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doi:10.2134/agronj1972.00021962006400030042x

Determining Nitrate in Forage Samples by Xylenol Nitration1

  1. L. D. Sabatka,
  2. D. N. Hyder,
  3. C. V. Cole and
  4. W. R. Houston2

Abstract

Abstract

The xylenol method of determining nitrates in water samples was reported to provide advantages of rapidity, specificity, sensitivity, and reproducibility. Since most methods of determining nitrates in forage samples are difficult and time consuming, our objective was to adapt the xylenol method for determining nitrates in forage and to compare it to the nitrate-electrode method.

The first problem originated from an incorrect procedural suggestion concerning the ratio of sulfuric acid to water in the nitration medium. The original recommendation for six parts of sulfuric acid to four parts of water and two parts of acetic acid was satisfactory.

The second problem was one of clarifying plant extracts without adding interfering ions or removing nitrate. A source of bone black adsorbed plant pigments without adsorbing nitrate.

The third problem was that of interference from sugar, which required quantitative evaluation. Although the amount of that interference was small, amounting to 5.4 ppm of nitrate N per 1% sugar extracted from plant dry matter, it was important in the comparison of xylenol and nitrate-electrode methods. A rapid colorimetric method of determining extracted sugar by darkening with sulfuric acid was developed.

Among triplicate determinations of 12 forage samples ranging from 87 to 1,469 ppm of nitrate N, the xylenol and nitrate-electrode methods gave equal values and time requirements, but the standard deviation for repeatability was ± 29 ppm by the xylenol method and ± 63 ppm by the nitrate electrode. Consequently, the xylenol method was considered sufficiently accurate, rapid, and precise for routine determinations of nitrate concentrations in forage samples.

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