セレンを触媒とするケルダール窒素定量法の改良

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Since the discovery by M. F. Lauro that selenium is an effective catalyst in Kjeldahl nitrogen determinations, many investigators have devoted additonal study to its use, and several of them have found that on long heating this element is liable to reduce the amount of nitrogen obtained in the analysis. To obviate the danger of loss of nitrogen, A. E. Beet and D. G. Furzey have suggested the use of a mixed selenium-mercury catalyst which materially shortens the digestion period, and they have also suggested a mere 10 minutes' "after boil." Such a catalyst, however, necessitates the use of a precipitant for mercury. The present paper deals with the results obtained when selenium is used with copper sulphate and phosphoric-sulphuric acid. In the experiment gas heat was used. 10 cc of phosphoric-sulphuric acid (this was prepared by dissolving 200 gms of anhydrous phosphoric acid in 1 litre of concentrated sulphuric acid) and 0.3gm of the catalyst mixture, consisting of an equal part of selenium and copper sulphate, were added to each sample (0.1 gm of pure organic compounds and 0.5 gm of natural organic substances) to be digested. Comparisons were made, both as regards speed and accuracy, between the copper sulphate method, the selenium method and the writer's new method. From the resuts obtained in this investigation it may be stated that the new method has the following advantages. 1. The digestion periods are considerably shortened so that it can be accomplished in 30 minutes or less ; 7-15 minutes is used to clear the liquid and 15 minutes suffices for the "after・boil." Compared with the copper sulphate method, the time of digestion taken by the new method is from 1/2 to 2/3 less without impairing the accuracy of the determination. 2. This method does not require the use of a precipitant in distillation. 3. Copper sulphate in the catalyst mixture serves as an indicator when concentrated sodium hydroxide is added to the acid before distillation, and the excess of the hydroxide can be saved.
社団法人日本土壌肥料学会の論文
1937-04-15

セレンを触媒とするケルダール窒素定量法の改良

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