Determination of Trace Amount of Fluorine in Unpolished Rice by Means of Oxygen Bomb-Fluoride Ion-selective Electrode

Abstract

A simple method has been developed for the determination of fluoride ion in unpolished rice by fluoride ion-selective electrode after pretreatment of the sample using oxygen bomb combustion.
A trace amount of fluoride ion can be determined as follows; The sample was burned in an oxygen bomb (25kg/cm²) conventionally using 10ml of water as a absorber. The ionic strength was adjusted with 10ml of 1, 2-cyclohexanediamine-tetraacetic acid buffer solution and the solution was filled up 25ml with water. The fluoride activity was measured by fluoride ion-selective electrode 20min after start of measurement. Effect of diverse ions on determination of fluoride ion was preliminarily examined, and the upper limits of concentration of them were found.
Reprobability of this method was satisfactory. Coefficient of variation was 0.9% and recovery was 92-103%. The trace amount of fluoride ion in unpolished rice in Fukui prefecture ranged from 1.4 to 2.0ppm.