22
Fluoride Ion Selective Electrode User Guide
Low-Level Calibration and Measurement When Using a Meter
with Millivolt Mode
1. Measure 50 mL of deionized water and 50 mL of low-level
TISAB and add to a 150 mL beaker.
2. Rinse the electrode with deionized water and place into
beaker. Stir the solution thoroughly.
3. Add increments of the 10 ppm or 10
-3
M fl uoride standard
mixed with low-level TISAB to the beaker using the steps
outlined in
Table 2
. Record the stable millivolt reading after
each increment.
4. Using a calculator or or electronic spreadsheet, prepare
a calibration curve by graphing the log of the fl uoride
concentration against the millivolt value readings. Prepare a
new calibration curve with fresh standards each day.
5. Measure 50 mL of sample and 50 mL of low-level TISAB
and add to a clean 150 mL beaker. Rinse the electrode with
deionized water, blot dry and place into the sample.
6. Stir the solution thoroughly. When a stable reading is
displayed, record the mV value.
7.
Determine the sample concentration corresponding to the
measured potential from the low-level calibration curve.
Table 2 Calibration Curve For Low-Level Measurements
Additions of standard (with low-level TISAB) to 50 mL distilled
water and 50 mL low-level TISAB solution.
Concentration
Step
Pipette
Size
Volume
Added
ppm
M
1
1 mL
0.1 mL
0.01
1 x 10
-6
2
1 mL
0.1 mL
0.02
2 x 10
-6
3
1 mL
0.2 mL
0.04
4 x 10
-6
4
1 mL
0.2 mL
0.06
6 x 10
-6
5
1 mL
0.4 mL
0.10
1 x 10
-5
6
2 mL
2.0 mL
0.29
2.9 x 10
-5
7
2 mL
2.0 mL
0.48
4.8 x 10
-5
