eutech-instruments fluoride epoxy Manuale Utente

Instruction Manual 

 

Fluoride Electrode

 

 

5

Slope is defined as the change in potential observed when the concentration changes by a factor of 
10. 
 

(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 

 section if the slope is not 

within this range. 

 

 
MEASUREMENT 
 

 
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.