The rapid measurement of fluoride concentrations in stored human saliva by means of a differential electrode cell

Abstract

For the purpose of rapid measurement, the performance of a differential cell, consisting of a combination pH electrode and a F − electrode and used at low pH (1.2), was compared with the use of a single F − electrode at pH 5.0. The differential cell proved to be as accurate and consistent as the single electrode: its response time was 2 min for a saliva volume of 50 μl; the response time of the single electrode was 20 min with a saliva volume of 1000 μl. Analysis of salivary supernatant fluid provided an unreliable guide to the original salivary F − concentrations but if fresh whole saliva was acidified to pH 1.2 immediately upon collection, the original baseline values were repeatedly obtained when measurements were made at intervals over a storage period of 14 days at 4 °C. Immediate acidification thus provides a satisfactory method for collecting samples from separate populations and then transporting them at leisure to a laboratory for direct measurement at pH 1.2 with the differential cell.