Instruction Manual
Potassium Electrode
10
Electrode drift and slow response could indicate the presence of high interference from the ions
listed. Soak the electrode(s) in distilled water for an hour, then for two hours in potassium standard
solution to restore proper response.
TABLE 3: Concentration of Possible Interferences Causing a 10% Error at
Various Levels of KCl; Background Ionic Strength is 0.12M NaCl.
Interferences
(moles/liter) 10
-2
M K
+1
10
-3
M K
+1
10
-4
M K
+1
Cs
+1
3.0X10
-3
3.0X10
-4
3.0X10
-5
NH4
+1
6.0X10
-2
6.0X10
-3
6.0X10
-4
Tl
+1
6.0X10
-2
6.0X10
-3
6.0X10
-4
H
+1
1.0X10
-1
1.0X10
-2
1.0X10
-3
Ag
+1
1.0X10
1
1.0
1.0X10
-1
+Tris
+1
1.0X10
1
1.0
1.0X10
-1
Li
+1
2.0X10
1
2.0
2.0X10
-1
Na
+1
2.0X10
1
2.0
2.0X10
-1
+Tris
+1
is the cation of tris (hydroxymethyl) aminomethane
Interferences
(ppm)
100 ppm K
+1
10 ppm K
+1
1 ppm K
+1
Cs
+1
1.0X10
2
1.0X10
1
1.0
K
+1
2.7X10
2
2.7X10
1
2.7
Tl
+1
3.1X10
3
3.1X10
2
3.1X10
1
H
+1
1.6 pH
2.6 pH
3.6 pH
Ag
+1
2.7X10
5
2.7X10
4
2.7X10
3
+Tris
+1
3.1X10
5
3.1X10
4
3.1X10
3
Li
+1
3.5X10
4
3.5X10
3
3.5X10
2
Na
+1
1.1X10
5
1.1X10
4
1.1X10
3
Temperature Influences
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
level.
Provided that temperature equilibrium has occurred, the potassium electrodes can be used at
temperatures from 0
o
-50
o
C continuously and 40
o
-50
o
C intermittently. Room temperature
measurements are recommended, since measurements at temperatures markedly different from
room temperature may require equilibrium times up to one hour. Table 4 indicates the variation of
theoretical slope with temperature.