6
Fluoride Ion Selective Electrode User Guide
Checking Electrode Operation (Slope)
These are general instructions that can be used with most
meters to check the electrode operation. Refer to the meter
user guide for more specifi c information.
This procedure measures electrode slope. Slope is defi ned
as the change in millivolts observed with every tenfold change
in concentration. Obtaining the slope value provides the best
means for checking electrode operation.
1. If the electrode has been stored dry, prepare the electrode
as described in the
Electrode Preparation
section.
2. Connect the electrode to the meter. Set the meter to the
mV mode.
3. Place 50 mL of distilled water and 50 mL of TISAB II (Low-
level TISAB or TISAB IV) into a 150 mL beaker. Stir the
solution thoroughly.
If using TISAB III, place 90 mL of distilled water and
10 mL of TISAB III into a 150 mL beaker. Stir the solution
thoroughly.
4. Rinse the electrode with distilled water and place the
electrode into the solution prepared in step 3.
5. Select either a 0.1 M sodium fl uoride or 100 ppm fl uoride
standard. Pipette 1 mL of the standard into the beaker and
stir thoroughly. When a stable reading is displayed, record
the electrode potential in millivolts.
6. Pipette 10 mL of the same standard into the same beaker
and stir thoroughly. When a stable reading is displayed,
record the electrode potential in millivolts.
7. There should be a 54 to 60 mV difference between the
two millivolt readings when the solution temperature is
between 20 to 25 ˚C. If the millivolt potential is not within
this range, refer to the
Troubleshooting
section.
