Thermo Fisher Scientific Ion Selective Electrodes Fluoride - Manual (Page 6)

Instruction Manual Fluoride Electrode
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Slope is defined as the change in potential observed when the concentration changes by a factor of
10.
Electrode Slope Check (with ion meter)
(Check electrodes each day)
1. Prepare standard fluoride solutions whose concentrations vary by tenfold. Use either the
0.1M, 1,000 ppm, or 100 ppm fluoride standard. Use the serial dilution method for this
preparation.
2.
To a 150 ml beaker, add 50 ml of the lower value standard and 50 ml of TISAB. Place the
beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips
into the solution. Assure that the meter is in the concentration mode.
3.
Adjust the meter to the concentration of the standard and fix the value in the memory
according to the meter manufacturer's instructions.
4.
Rinse the electrodes with distilled water and blot dry.
5.
To another 150 ml beaker, add 50 ml of the higher value standard and 50 ml of TISAB.
Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the
electrode tips into the solution.
6.
Adjust the meter to the concentration of the standard and fix the value in the memory.
7.
Read the electrode slope according to the meter instructions. Correct electrode operation is
indicated by a slope of 90-100%. See the
TROUBLESHOOTING section if the slope is not
within this range.
MEASUREMENT
Measuring Hints
All samples and standards should be at the same temperature for precise measurement. A difference
of 1
o
C in temperature will result in a 2% measurement error.
Constant, but not violent, stirring is necessary for accurate measurement. Magnetic stirrers can
generate sufficient heat to change the solution temperature. To counteract this effect, place a piece
of insulating material, such as a styrofoam sheet, between the stirrer and the beaker.
Always rinse the electrodes with distilled water and blot dry between measurements. Use a clean,
dry tissue to prevent cross-contamination.
For samples with high ionic strength, prepare standards whose composition is similar to the sample.
Always check to see that the membrane is free from air bubbles after immersion into standard or
sample.