Metrohm tiamo 1.1 Manual - Manual (Page 352)

324 Method
Evaluation
Equivalence points (EPs) are determined atuomatically in a similar manner to that
described in the Tubbs method (C.F. Tubbs; Anal. Chem 26 (1954) 1670–1671,
quoted in Ullman 5 (1980) 659). The volume of the equivalence point (V
E
) is shifted
from the point of inflection towards the smaller circle of curvature for real asym-
metric titration curves.
The figure shows that the evaluation also requires measuring points after the
equivalence point too.
For the recognition of the EPs found the set
EP criterion is compared with the ERC
( E quivalence point R ecognition C riterion) found. The ERC is the first derivative of
the titration curve combined with a mathematical function which is more sensitive
for flat jumps than for steeper ones. EPs whose ERC is smaller than the set EP cri-
terion will not be recognized.
Commands
Depending on the measured value one of the following four DET commands can
be chosen:
• DET pH
Potentiometric pH measurement with pH electrodes (measured quan-
tity pH).
• DET U
Potentiometric voltage measurement with metal electrodes (measured
quantity voltage U).
• DET Ipol
Voltametric measurement with selectable polarization current (meas-
ured quantity voltage U).
• DET Upol
Amperometric measurement with selectable polarization voltage
(measured quantity current I).