eutech-instruments calcium epoxy ユーザーズマニュアル

Calcium Electrode 

 

Instruction Manual 

 

12

  

Interferences 

      

     (ppm)           1,000 ppm CaCO

3

     100 ppm CaCO

3

     10 ppm CaCO

3

 

 Mg

+2

 2.43X10

5

 2.43X10

4

 2.43X10

3

 

 Zn

+2

 6.53X10

5

 6.53X10

4

 6.53X10

3

 

 Ba

+2

 9.60X10

5

 9.60X10

4

 9.60X10

3 

 

K

+1

 1.56X10

5

 1.56X10

4

 1.56X10

3

 

 Na

+1

 4.60X10

4

 4.60X10

3

 4.60X10

2

 

 Ni

+2

 2.94X10

4

 2.94X10

3

 2.94X10

2 

 Cu

+2

 2.54X10

4

 2.54X10

3

 2.54X10

2 

 Fe

+2

 1.11X10

4

 1.11X10

3

 1.11X10

2 

 Sr

+2

 5.20X10

3

 5.20X10

2

 5.20X10

1 

 

H

+1

 

1.4 pH 

2.4 pH 

3.4 pH 

 Hg

+2

 8.0X10

3

 8.0X10

2

 8.0X10

1

 

 Pb

+2

 2.0X10

1

 2.0 

2.0X10

-1 

 
Sulfate, bicarbonate, and carbonate are the most common species that complex calcium ions.  The 
level of calcium ions, the level of the complexing ion, the pH of the solution, and the total ionic 
strength of the solution determine the extent of the complexation. Complexation reduces the free 
calcium ion concentration and, since the electrode responds only to free calcium ions, a false 
reading results. 
 
To avoid formation of CaSO

4

, the sulfate concentrations must be less than 5X10

-4

M (50 ppm). To 

avoid formation of CaCO

3

 or formation of the CaHCO

3

+

 complex, the pH of the solution should be 

less than 7, and the total carbonate/bicarbonate concentration should be less than 3X10

-3

M (280 

ppm carbonate). 
 

 
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 4% error at the 1.0X10

-3

M 

level. 
 
Provided that temperature equilibrium has occurred, the calcium electrodes can be used at 
temperatures from 0

o

-40

o

C. Room temperature measurements are recommended, since 

measurements at temperatures quite different from room temperature may require equilibrium times 
up to one hour. Table 4 indicates the variation of theoretical slope with temperature. 
 
            TABLE 4: Temperature vs. Value for the Electrode Slope 
 
                 Temp (

o

C)       

 "S" 

                     0           

27.10 

                    10           

28.10 

                    20           

29.08 

                    25           

29.58 

                    30           

30.07 

                    40           

31.07