Measurement in the non-linear region of the calibration graph of the fluoride ion-selective electrode by blank adjustment

Abstract

A method is described that permits the determination of low levels of fluoride with a fluoride ion-selective electrode, in the non-linear response region, but avoids the use of non-linear calibration. An estimate of the background response of the fluoride ion-selective electrode is obtained by multiple standard additions. Adjustment of the fluoride standard values with this background estimate results in a linear calibration graph. Fluoride levels in samples are then easily determined by linear interpolation and correction for background response, irrespective of whether this is due to fluoride contamination of reagents or hydroxide interference from buffer pH.