Hanna Instruments HI 8521 - Manual (Page 29)

29
Alkaline Error
1.0 Mol L -1 Na +
0.1 Mol L -1 Na +
Sodium Ion Correction for the Glass at 20-25°C
Concentration pH Error
13.00
13.50
14.00
12.50
13.00
13.50
14.00 0.10
0.14
0.20
0.10
0.18
0.29
0.40
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 the
alkaline error and causes the pH to be underestimated. Hanna's glass
formulations have the indicated characteristics.