The Magnesium Problem in Nitrate Determination by Steam Distillation
1980
Clausen, C. | Bock, B. R. | Peterson, G. A. | Olson, R. A.
Steam distillation of NH₃ is commonly used to quantify the amount of mineral N in soil and plant materials. A problem with NO₃⁻ recovery by this method was encountered in an NH₃ volatilization study. When NH₄NO₃ solutions were collected in acid and analyzed for NH₄⁺-N and NO₃⁻-N, incomplete recovery of NO₃⁻ occurred. As the volume or normality of H₂SO₄ added to the distilling solution increased, more of the MgO used to raise the pH of the distilling solution was solubilized, which caused NO₃⁻ recovery in the first 25ml of distillate to decrease. Only 80% NO₃⁻-N recovery was obtained with 20 ppm of Mg²⁺ in the distilling solution. Soils with 3 meq exchangeable Mg²⁺/100 g depressed NO₃⁻-N recovery by 15% using the standard distillation procedure. An interaction between Mg²⁺ and Devarda's alloy evidently inhibits NO₃⁻ reduction.
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