Determination of oxygen in sodium by the amalgamation method with special reference to blank values

• Published in: BUNSEKI KAGAKU Vol. 21; no. 7; pp. 860 - 867
• Main Authors: IZAWA, Kimie, AOYAGI, Hisao, YOSHIDA, Zenko, TAKAHASHI, Masao
• Format: Journal Article
• Language: Japanese
• Published: The Japan Society for Analytical Chemistry 05.07.1972
• ISSN: 0525-1931
• DOI: 10.2116/bunsekikagaku.21.860

Amalgamation method for determination of oxygen in sodium has been examined with special reference to blank values. Although the method is the most widely used for determining oxygen in sodium, several unsolved problems, especially blank correction are encountered in the application of the technique. Consequently, effects such as atmosphere purity in the glove box for handling sodium, surface area of amalgamation vessel, purification method of mercury, and sampling tube on the blank values were examined. Among these experimental conditions described above, only one condition, for example, surface area of the amalgamation vessel, was varied while keeping the others constant. Oxygen-free amalgam which was prepared by mixing sodium with mercury in the ratio of 1g of sodium to 15ml of mercury and separating the oxide impurities by flotation was used as the sample for blank test. The blank value obtained under the conditions in which one variable was changed was compared with that of standard routine procedure as the reference. If significant difference was found between two blank values, it was considered that the variable contributed to a total blank. When the inner surface area of amalgamation vessel was varied, the blank value obtained by using a large amalgamation vessel (218cm2), which was used in standard routine procedure, was 8.5±0.9μg of oxygen and 6. 8±1.1μg of oxygen for small one (135cm2). As a result of experiments, which were shown in Table I, it was found that 4.5μg of oxygen was caused by absorbed water on inner surface of the large amalgamation vessel and 2.8μg of oxygen for the small one. One to three μg of apparent oxygen, which may come from contamination of sodium oxide during the glove box operation, was also observed when the standard procedure was performed by carrying only mercury instead of oxygen-free amalgam through the entire procedure. On the other hand, Tables II and III showed that argon atmosphere containing no more than 1ppm each of moisture and oxygen did not contribute to blank value, but when oxygen-free amalgam was treated under argon atmosphere containing 7 and 40ppm of moisture and oxygen, respectively, the blank increased threefold. Effects of purification methods of mercury, i.e., distillation and filtration, and also of drying method of amalgamation vessels on the blank values were not serious as shown in Tables IV and V. Apparent oxygen from stainless steel sampling tube was measured by adding an empty sampling tube into oxygen-free amalgam and was found to be less than 0.5μg of oxygen per 12.7φ×15mm stainless tube which can contain 1g of sodium. The blank value obtained by intercept method agreed well with that by using oxygen-free amalgam. However, in actual analysis it was advisable to measure the blank value by using oxygen-free amalgam because of possible segregation of oxygen in sodium.