MICRODETERMINATION OF FLUORINE IN ORGANIC COMPOUNDS

In this paper a method for the microdetermination of flurine in organic compounds is reported. This method was established in 1966, many years' practice has shown that it is simple, rapid and the end point is sharp. Thus the method is suitable fbr routine analysis of organic fluoro-compounds.The sample, containing 0.5 to 1.5 mg of fluorine, is burned in a Schniger flask with dilute NaOH solution as absorbent. In this way, it is unnecessary to use quartz flask as the combustion flask and the analytical results are better than using water as the absorbent. After combustion, the solution is made acidic with dilute nitric acid, the fluoride ion is precipitated with an excess of Ce (Ⅲ) solution. The pH of the solution in the presence of ethyl alcohol is adjusted to 5.6±0.4 with urotropine. The excess of Ce (Ⅲ) is back-titrated with a standard EDTA solution (0.005 M) with xylenol orange as indicator screened with methylene blue. Nitrogen and other halogens do not interfere with this determination. The effect of sulfate can be eliminated by adding an excess of barium chloride without filtering the precipitate formed. A single determination can be completed within 30 minutes. The analytical values are within the usual limits of error, namely 0.3% absolute.