Lead chlorofluoride, determination fluorine using

In each class the problem may be resolved into two essential parts (i) the breakdown of the organic compound under appropriate conditions to give a quantitative yield of fluoride ions in aqueous solution, and (ii) the determination of the concentration of these fluoride ions. Methods of breaking down the organic compounds were examined and the procedure adopted for the phosphorofluoridate was different from that used for the fluoroacetate series. From both, however, sodium fluoride was obtained as the breakdown product containing all the fluorine present. After numerous preliminary experiments we came to the conclusion that on the macro-scale a very convenient method of determining the quantity of fluoride ions in the products was by precipitation as lead chlorofluoride,2 PbCIF, which was then dissolved in dilute nitric acid and the chloride was determined by the Volhard method and calculated to the equivalent amount of fluorine. We determined carefully the conditions for the quantitative precipitation of lead chlorofluoride. 

A sample placed behind a 25 jum copper beam intensity monitor is irradiated for 15-20 min with a 2 mA beam of 25 MeV He. By chemical etching in 6 M nitric acid a 25-50 Asurface layer is removed. The sample is dissolved in 14 M nitric acid to which some sodium fluoride, zinc nitrate and gallium oxide carrier are added. After addition of phosphoric acid, the temperature is raised to 125° and 150 ml of distillate are collected. Gallium oxide is added to the distillate and gallium hydroxide is precipitated and filtered off. Finally, fluorine is precipitated as lead chlorofluoride The precipitate is repeatedly measured with a Ge(Li) detector during a 10 h period to allow the control of the half-life. Afterwards the yield of the chemical separation is determined by activation with an Ac-Be isotopic neutron source using the F(n,a) N reaction. 

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