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Alkaline Error
High concentrations of sodium ions interfere with readings in alkaline
solutions. The pH at which the interference starts to be significant
depends upon the composition of the glass. This interference is called
alkaline error and causes the pH to be underestimated. Hanna Instru‑
ments' glass formulations have the indicated characteristics.
Sodium Ion Correction for the Glass at 20‑25 ºC (68-77°F)
Concentration
0.1 Mol L
Na
‑1
1.0 Mol L
Na
‑1
+
+
pH
13.00
13.50
14.00
12.50
13.00
13.50
14.00
21
Error
0.10
0.14
0.20
0.10
0.18
0.29
0.40
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