Determination of nitrogen in soil and plant materials: Use of boric acid in the micro-kjeldahl method
Determination of nitrogen in soil and plant materials: Use of boric acid in the micro-kjeldahl method
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DOI：
10.1002/jsfa.2740041006
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发表时间：
1953-10
影响因子：
4.1
通讯作者：
S. Yuen;A. Pollard
中科院分区：
文献类型：
--
作者：
S. Yuen;A. Pollard
本文研究了用硼酸捕集微量凯氏定氮中的氨。一个合适的程序，连同一个修改类型的微蒸馏装置，进行了描述。硼酸溶液的缓冲能力与溶解在其中的氨滴定的灵敏度有关。两个等级的硼酸，“纯”（技术）和AnalaR，进行了比较;前者表现出明显的缓冲酸侧。两个等级的溶液的pH值随浓度的增加而降低。由于缓冲作用的增加，用于氨滴定的三种指示剂的灵敏度随着硼酸浓度的增加而降低。使用浓硼酸时，所有三种指示剂在终点处显示出宽的过渡期，但在浓度高达1-0% AnalaR级的溶液中，所有三种指示剂显示的终点都是尖锐的。然而，亚甲基蓝-甲基红指示剂通常是优选的。通过空气鼓泡试验和蒸馏回收已知量的氨来研究硼酸的固氨能力。体积为10 ml。1-0%硼酸固定5 mg.氮作为氨足够牢固，以提供准确的分析。对于大量测定，100 ml。2-0%的硼酸牢牢地保持高达90毫克。氮。
The use of boric acid for trapping ammonia in the micro-Kjeldahl determination is examined. A suitable procedure, together with a modified type of micro-distillation apparatus, is described. The buffer capacity of boric acid solutions was examined in relation to the sensitivity in the titration of ammonia dissolved in them. Two grades of boric acid, ‘pure’ (technical) and AnalaR, were compared; the former showed appreciable buffering on the acid side. The pH values of solutions of both grades decreased with increasing concentration. The sensitivity of the three indicators examined for the titration of ammonia diminished with increasing concentration of boric acid as a result of the increased buffering. With concentrated boric acid, all three indicators showed wide transitional periods at the end-point, but in solutions of concentration up to 1-0% of AnalaR grade the end-points shown by all three indicators were sharp. The methylene blue-methyl red indicator, however, was generally preferable. The ammonia-fixing capacity of boric acid was studied in air-bubbling tests and by recovery of a known amount of ammonia by distillation. A volume of 10 ml. of 1-0% boric acid fixed 5 mg. of nitrogen as ammonia sufficiently firmly to afford accurate analyses. For macro-determinations, 100 ml. of 2-0% boric acid held firmly up to 90 mg. of nitrogen.