1. Briska, M., Hoffmeister, W.: Mikrochim. Acta 1974, 815–818
2. Fresenius, W., Jander, G.: Handbuch der Anal. Chemie, Bd. III (Bor). Berlin-Heidelberg-New York: Springer 1971
3. Grether, C.: Application Bulletin Nr. A 66 d. Fa. Metrohm, Herisau/Schweiz
4. van Liempf, J. A. M.: Z. Anorg. Allg. Chem. 111, 151–166 (1920)
5. Matheson Gas Data Book, 5th. Ed., S. 175 (1971)