(II) Methods of Microdetermination of Fluorine

Abstract

In studying chronic fluorine poisoning, determination of microquantity of fluorine is significant, and a study was carried out in this respect. Both bleaching colorimetry of Th-Alizarin and photoelectro-colorimetric titration were improved, and conditions for increasing the accuracy were determined. This method was based on the reaction F-with Th-Alizarin lake, utilizing the phenomenon which quantitatively changes with the density of the lake by letting F- form a colorless complex ion with Th⁺⁺⁺⁺. The method used was considered appropriate for determination of microquantity of fluorine, the result thus obtained are as follows. 1. Titration is suitable as a routine work, for the quantity-examination line becomes straight. 2. With both methods, measurement will be possible down to 0.1γ/25ml (0.004 p.p.m.). 3. Over the range of F- 0∼20γ/25ml, repeatability is possible to 95∼105%. 4. Measurement should be undertaken exactly five minutes after the coloring of the lake. 5. Hydrogen iou concentration will greatly affects the accuracy and precision, and thus measurement should be undertaken at pH 3.00. 6. In photoelectro-colorimetric titration, the endpoint was fixed at E=0.080 for improving precision. 7. The extent of the effect of interfering ions was small in Cl^-, Ca⁺⁺, NH₄⁺, medium in Mg⁺⁺, SO₄^-- and extremely high in Al⁺⁺⁺, HPO₄^--.