Fluoride in Water

Fluoride is dosed into the potable water supply to improve dental health. It is therefore essential to ensure these levels are correct. It also means that Fluoride is then present in products where tap water is used in production. Fluoride is used in glass etching and Hydrofluoric acid is a commonly used in many different industries including metal reclamation or stripping. The Fluoride ISE is the best way to quantify the concentration with confidence.

Image showing an ion meter.
Image showing a combination Ion Selective Electrode.

Fluoride in Water Method

A rapid and simple method for the measurement of fluoride concentration in water in the range of 0.1 – 100ppm.

Equipment Required

1.   Model QP459 Portable ION Meter

2.   3221 Fluoride Combination ISE

3.   21333 Fluoride 1000ppm Standard Solution

4.   30333 Total Ionic Strength Adjustment Buffer (TISAB)

5.   Glassware. Beakers 250ml, Volumetric Flask 100ml. 10ml pipette

6.   Deionised water.

Standard Preparation

Prepare standards of 100, 10, 1 and 0.1ppm  Fluoride  by serial dilution of the 21333 Fluoride 1000 ppm standard. This is achieved by pipetting 10ml of the  top standard into a 100ml volumetric flask and diluting to the mark with deionized water. This is now a 100ppm Standard solution. Repeat in series to prepare the required standards.

Method

The QP459 ION meter has a direct Fluoride ISE mode. The result is displayed in ppm and calibration is automatic using 1, 10 and 100ppm Standards.

To 50ml of each of the prepared standards and samples add 10ml of 30333 TISAB and mix the contents. Be sure the beakers are clean and make sure not to touch the inside of the beakers with bare hands as contamination from sweat etc. is common. Beakers that have been washed with softened water or tap water will be contaminated. In these cases rinse the beakers with deionised water.

Immerse the 3221 Fluoride Combination electrode in each of the standards in increasing concentration steps in the calibration mode of the Ion Meter, rinsing the electrodes with distilled water and dabbing off the excess water between standards.

Using the QP459 Ion meter will allow the result to be read directly on the display.

Fluoride in tap water is typically 0.5 to 1ppm. There are many applications with higher concentrations e.g. Fluoride in Toothpaste. The samples can be diluted as necessary with deionised water.