eutech-instruments fluoride epoxy Manuale Utente

Instruction Manual 

 

Fluoride Electrode

 

 

10

2. 

Following the directions given in the preceding 

section

  (Determination of Fluoride    in 

), prepare standards, calibrate the electrodes and measure the unknown 

samples. 

 

 
Use the following low level fluoride measurement procedure in the non-linear portion of the 
calibration curve. (See Figure 1.) This procedure is used for fluoride samples containing less than 
2X10

-5

M or 0.4 ppm fluoride and containing no fluoride complexing agents. Use low level TISAB 

2 for both samples and standards. A longer response time should be expected for low level fluoride 
measurements. 
 

1. 

By serial dilution, prepare a 1.0X10

-3

M or 10 ppm fluoride standard by diluting the 0.1M, 

1,000 ppm, or 100 ppm standard solution. Add 50 ml low level TISAB 2 to 50 ml of 
standard solution. 

 
2. 

Using a 150 ml beaker, add 50 ml of distilled water and 50 ml of low level TISAB 2.  
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 mV mode. 

 
3. 

Increments of the standard should be added to the beaker according to the steps outlined in 
Table 2 below. After the reading stabilizes, record the mV reading for each addition. 

 

    TABLE 2: Low Level Measurement Calibration Curve 

 
                                

 

1          A          

0.1            

0.01       1.0X10-6 

           

2          A            

0.1            

0.02       2.0X10-6 

           

3          A           

0.2            

0.04       4.0X10-6 

           

4          A           

0.2            

0.06       6.0X10-6 

           

5          A           

0.4            

0.10       1.0X10-5 

           

6          B            

2.0            

0.29       2.9X10-5 

           

7          B           

2.0            

0.48       4.8X10-5 

 
 

Pipet A   = 1 ml graduated pipet 

 

Pipet B   = 2 ml pipet 

 

Solutions:  additions of standard / TISAB 2 to 50 ml of distilled water 

 

 

     and 50 ml of low level TISAB 2. 

 

4. 

On semi-logarithmic graph paper, plot the concentration (log axis) against the millivolt 
reading (linear axis) as in Figure 1. Keep the final solution for checking the electrode 
calibration. 

 
5. 

To a 150 ml plastic beaker, add 50 ml of sample and 50 ml of low level TISAB 2. Place the 
beaker on a magnetic stirrer and begin stirring. After rinsing the electrodes and blotting 
dry, place the electrode tips into the solution. After stabilization of the reading, read the 
mV potential and determine the concentration from the calibration curve. A new low level 
calibration curve should be prepared daily using fresh standards.