Determination of fluoride in aqueous solutions of sodium monofluorophosphate with an ion-selective electrode

Abstract

The reported interference by monofluorophosphate in the determination of fluoride by the fluoride ion-selective electrode has been re-investigated and it has been shown that in samples of controlled ionic strength little inference occurs.

Buffer systems based on acetate, citrate and TISAB were examined; although little difference was found in the results obtained using acetate and TISAB, the known inhibition of monofluorophosphate hydrolysis in acetate buffer of pH 5.2 and its suitability for use in orthophosphate determination in monofluorophosphate solutions suggest that this buffer system may be preferable for the determination of fluoride by ion-selective electrode in the presence of monofluorophosphate ions.

The results obtained using a computerised linear regression technique have been compared with those obtained using a manually plotted and visually read calibration graph and it is concluded that the former method is preferable.