Instruction manual

Interferences
Sodium ion is the principal interference for the pH electrode,
causing increasing error at higher pH (lower hydrogen ion activities)
and at higher temperatures. Because the ROSS
™
pH membrane is
composed of special low-sodium error glass, error due to sodium is
negligible when measuring at pH values less than 12. When
measuring at pH values greater than 12, add the correction value
from the nomograph in Figure 6 to the observed pH reading.
Figure 3: Typical Sodium Error Observed at pH >12
Example:
pH reading 12.10
Sodium concentration 0.5N
Temperature 50 ˚C
Correction 0.01
Corrected pH reading 12.11
14
10
11
12
13
80
70
60
50
40
30
°C 20 0.1 M
25
0.5 M
1 M
2 M
5 M
5 M
0.5 M
0.1 M
1 M
2 M
20°C
25
30
40
50
60
70
80
0.70
0.60
0.50
0.40
0.30
0.25
0.20
0.15
0.10
0.08
0.06
0.05
0.04
0.03
0.02
0.01
0.005
pH correction
to be added
Sample
pH reading
sample
sodium
concentration