Abstract
An electro-analytical study on the dynamic property of the fluoride-selective electrode has been carried out for the microdetermination of fluorine by means of direct potentiometric measurement of the fluoride activity in a sample solution. The electrode potential responded to the fluoride activity down to 10-4M with extremely fine traceability to the Nernstian slope and the potential was equilibrated within a few minutes after dipping the electrode into the solution. The reproducibility of the electrode potential was practically invariable for the concentration down to 10-4M and a fluoride concentration ranging 10-310-4M was the most preferable for 1001000 μg of fluorine because it made possible to make up the test solution to a convenient volume, 100 ml.
The method has been applied to the microdetermination of organic fluorine using oxygen flask combustion. A sample was burned in an oxygen flask conventionally using 10 ml of water as the absorption liquid. The liquid was transferred into a 100 ml volumetric flask with 50 ml of water. The ionic strength was adjusted by an addition of 100 ml of TISAB (buffer solution, Orion Research Inc., U. S. A.) by making up the final volume to 100 ml. The fluoride activity was then measured by a combination of the fluoride-selective electrode and a silver chloride reference electrode after 5 minutes of soaking in the test solution.
Analytical results using hard glass combustion flasks gave values approximately 8% relative lower than those by quartz combustion flasks. The possible interfering elements such as silicon, aluminum and calcium were detected by atomic absorption spectrometry while boron was detected by solvent extraction using Methylene Blue. The latter played the main role for giving above lower values because silicon, aluminum and calcium were detected in both hard glass and quartz flasks.
