Determination of Fluorine in Fluoro-Organic Compounds

An analytical procedure is described for the determination of fluorine in fluoro-organic compounds based on 1 decomposition of the sample by refluxing with sodium in 1-hexanol, and 2 titration of fluoride ion with thorium nitrate using sodium alizarin sulfonate as indicator. The analysis requires about thirty minutes. Four fluoro-organic compounds were analyzed. Fluorine in sodium fluoroacetate was about 3 above the calculated quantity values for methyl fluoroacetate were about 4 low. The average value for di-isopropylfluorophosphate was approximately 1 below the theoretical, while in beta-fluoroethanol the fluorine values averaged about 11 low. In all analyses the average deviation from the mean was about or - 2. Purified di-isopropylfluorophosphate in a 45 ethanol solution contained 0.15 fluoride ion, but no fluoride ion was found in either methyl fluoroacetate or beta-fluoroethanol. Samples from two lots of sodium fluoroacetate contained 8.5 sodium fluoride. In the hope of enhancing the color change at the end-point in the thorium nitrate titration, fifty-four dyestuffs in mixtures with sodium alizarin sulfonate were tested. Only one appears to be of value. A comparison of Solochrome Brilliant Blue BS with sodium alizarin sulfonate showed each indicator to have some advantage, depending on the concentration range of fluorine the former is more sensitive at lower contractions.