ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Determination of microquantities of fluoride ions by titration

V. Delmárová, L. Machů, M. Malinovský, and A. Moncmanová

Slovak Technical University, Bratislava

Abstract: A modified method based on titrn. with Th(NO₃)₄ is described. To 50 mL. of the sample 10 drops of 0.05% soln. of 2,5-dinitrophenol is added and the soln. is neutralized with 0.1N HCl to a colorless soln. of pH 4.0. Then 1.5 mL. 0.02% soln. of Alizarine S, 10 mL. 2N NaCl, and 1.5 mL. 0.1N HCl are added so that the pH is changed to 2.63. It is titrated with 0.004N soln. of Th(NO₃)₄ (contg. 72 mL. 0.1N HCl in 1000 mL. ) to a rosy color. The effect on the results was studied of NaCl, Alizarine S, pH, and the ratio of Th⁴⁺ to F^- at the equivalence point. It was detd. that each operator in the evaluation should use his own calibration curve, that Alizarine S should be of the same shipment, and that the results of 2 parallel detns. in 50 mL. sample contg. 0-80 γ ^F- differ by 0.2-0.4%, and up to 3.0% in a very unfavorable case.

Full paper in Portable Document Format: 1710-11a787.pdf (in Slovak)

Chemical Papers 17 (10-11) 787–794 (1963)