eutech-instruments iodide epoxy User Manual

Instruction Manual 

 

Iodide Electrode

 

 

10

 

 
Samples and standards should be at the same temperature since electrode potentials are influenced 
by changes in temperature. A 1

o

C difference in temperature results in a 2% error at the 1.0X10

-3

M 

concentration level. Because of solubility equilibrium on which the electrode depends, the absolute 
potential of the reference electrode changes slowly with the temperature. The slope of the electrode, 
as indicated by the factor "S" in the Nernst equation, also varies with temperature. Table 4 gives 
values of the "S" factor in the Nernst equation for the iodide ion. 
 
   

   TABLE 4:  Temperature vs. Values for the Electrode Slope 

 
           

Temp (oC) 

 

 

"S" 

   

 

 

0 

   54.2 

   

 

10 

   56.2 

   

 

20 

   58.2 

   

 

25 

   59.2 

   

 

30 

   60.1 

   

 

40 

   62.1 

   

 

50 

   64.1 

 
If changes in temperature occur, the electrodes should be recalibrated. 
 
The temperature range of the Eutech Iodide Ion Electrodes is 0

o

-80

o

C, provided that temperature 

equilibrium has occurred. If temperature varies substantially from room temperature, equilibrium 
times up to one hour are recommended. 
 

 
Plotting the electrode mV potential against the iodide concentration on semi-logarithmic paper 
results in a straight line with a slope of about 57 mV per decade.  (Refer to Figure 1.) 
 
The time needed to reach 99% of the stable electrode potential reading, the electrode response time, 
varies from several seconds in highly concentrated solutions to several minutes near the detection 
limit.  (Refer to Figure 2.)