Determination of total nitrogen in soil digest using a traacs 800 autoanalyzer

Abstract

Nitrogen is an essential plant nutrient and is available to the plant in the ammonium or nitrate form. In soil, nitrogen is present in many forms which can be transformed to ammonium or nitrate. A modified total nitrogen digestion is described, which includes a pretreatment step with potassium permanganate, sulfuric acid, and reduced iron. Potassium permanganate and sulfuric acid oxidizes the NO₂‐ to NO_3‐, and the addition of reduced Fe causes compounds with N‐N and N‐O linkages to be digested. The reduction of NO₃‐ to NH₄₊ is effected by nascent hydrogen generated by the reaction of reduced iron with sulphuric acid. A block digestor is used with a selenium‐copper catalyst to convert the nitrogen to ammonium. The ammonium in the plant digest is determined, using a TRAACS 800 AutoAnalyzer utilizing the Berthelot reaction, with a capacity of 100 samples per hour. This method was compared to the Technicon AutoAnalyzer AAI distillation method using Berthelot reaction, at a sampling speed of 40 per hour.

Notes

Supervisor, Research Analytical Laboratory, Department of Land Resource Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1.

Analytical Chemist, 55 Circle Road, Pointe Claire, Quebec, Canada H9R 1W9.