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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)

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