Metrohm 726 Titroprocessor - Manual (Page 111)

7. Titration and measuring modes
726 Titroprocessor, Instructions for use 105 105
7.3.5 Evaluation of pK and HNP values
From the data of the titration curve of an acid/base titration the acidic or ba-
sic strength of a sample can be determined. For this purpose the pK value
or the HNP value can be determined automatically. The following formula
applies:
pH = pK + log(a
B
/a
A
)
If a
B
= a
A
, then pH = pK.
The pK value determined is the volume at the half neutralization point, which
can be obtained from the titration curve. Careful calibration of the pH elec-
trode used is a precondition for a correct determination of the pK value.
In non-aqueous solutions the half neutralization potential (HNP) is often
used instead of the pK value. The HNP value is evaluated in the same way
as the pK value.
The various parameters for the MET modes are described in detail
on pages 143 to 147.