Automated determination of fluoride ion in the parts per milliard range

Fluoride, down to 2 ppM, has been determined by automated direct potentiometry using a fluoride ion-selective electrode. The method reduces the dilution and contamination effects of TISAB and takes the electrode response-time into consideration. The relative standard deviation for water samples is 1.5-1.8% and the recovery varies from 96 to 107%.