The rapid determination of nitrogen present as nitrate and ammonium is of great importance in the analysis of fertilisers, for often large numbers of nitrogen determinations have to be done. In the determination of total nitrogen, nitrate is reduced to ammonia with a reducing agent and the ammonia is liberated and distilled off by boiling with a strong alkali. If the reduction is carried out in alkali (e.g. with Devarda alloy and sodium hydroxide) these reactions proceed simultaneously.
An automatic apparatus** capable of handling up to 50 samples per hour can be easily constructed on the basis of the method of YOTRAFKE, KROLL AND BLOM~.
The principal advantage of this method over older procedures is the extremely small volume of solution used in the reduction and distillation and consequently the short distillation time. This allows an automatic rapid apparatus to be constructed. The small volume makes it possible to work with a small reaction vessel that can be placed in the distillation apparatus. The absence of large amounts of water that have to be distilled off allows the use of a high-efficiency absorber of small volume. To obtain the highest possible. speed in serial analysis, the determination is split up into 3 steps: pretreatment and weighing of the sample; reduction, distillation and absorption: and titration. These 3 functions arc performed simultaneously on:,consccutive samples: during the distillation of sample number n, sample number P-I is titrated and the operator weighs sample number n + I. This makes it possible for one operator to analyse up to 50 samples per hour, though the time per sample is approximately 3.5 min.
EXPISRIMENTAL
The operator puts the ground and weighed, or dissolved, sample containing not more than 30 mg of nitrogen, in the reaction vessel (Fig. I). Devarda alloy, water and an anti-foaming agent, e.g. silicone oil, are added. The vessel is placed in its correct position on a platform that can be raised by a pneumatic cylinder (Figs. 2 and3),