Thermo Fisher Scientific Ion Selective Electrodes Fluoride - Manual (Page 9)

Instruction Manual Fluoride Electrode
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Direct Measurement of Fluoride (using an ion meter)
1.
By serial dilution of the 0.1M, 1,000 ppm, or 100 ppm fluoride standard, prepare two
fluoride standards whose concentration is near the expected sample concentration. Add 50
ml of TISAB 1 or TISAB 2, to each 50 ml of standard. When calibrating, assume that the
added TISAB has no effect on the standard concentration.
2.
Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate.
Assure that the meter is in the concentration mode.
3.
Lower the electrode tips into the solution.
4.
Adjust the meter to the concentration of the fluoride standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the
reading.
5.
Rinse the electrodes with distilled water and blot dry.
6. Place the more concentrated solution on the magnetic stirrer and begin stirring at a
constant rate.
7.
Lower the electrode tips into the solution.
8.
Adjust the meter to the concentration of the fluoride standard and fix the value in the
memory according to the manufacturer's instructions after stabilization of the reading.
9.
For low level measurements, place the rinsed, dried electrodes into a solution containing
equal volumes of distilled water and TISAB 1 or TISAB 2 (or add 10 ml of TISAB 2 to
each 100 ml of distilled water). After stabilization, fix the blank value in the meter
according to the meter manufacturer's instructions.
10. After rinsing the electrodes and blotting dry, place the electrode tips into the sample
diluted with an equal volume of TISAB 1 or TISAB 2. After stabilization, read the
concentration directly from the meter display.
11. The calibration should be checked every 1-2 hours. Assuming no change in ambient
temperature, place the electrode tips in the first fluoride standard. After the reading has
stabilized, compare it to the original reading in Step 4 above. A reading differing by more
than 0.5 mV or a change in ambient temperature will necessitate repetition of Steps 2-8 (2-
9) above. The meter should be re-calibrated daily.
Direct Measurement of Fluoride in Water (ASTM D1179, METHOD B)
The procedure is used to determine total fluoride concentration in water in ppm. TISAB is added to
standards and to samples in order to break fluoride complexes of iron and aluminum, adjust the pH,
and provide a constant ionic strength. Fluoride sample concentration is determined, using this
method, independent of the level or nature of dissolved minerals.