Metrohm 796 Titroprocessor - Manual (Page 113)

7. Titration and measuring modes
796 Titroprocessor, Instructions for use 107 107
7.4 SET Titration to a preset endpoint
Application:
SET modes are rapid titration modes for titrations to a preset endpoint. They
correspond to manual titrations and are suitable for rapid determinations of
non-critical samples.
Their typical feature is controlled reagent dosing depending on the control
difference (actual value – endpoint) with the aim of reaching the preset value
defined as the endpoint as quickly and accurately as possible. Overshoot-
ing is virtually eliminated. No automatic endpoint recognition is carried out.
Important: the endpoint should be selected so that it is near a point of in-
flection of the expected titration curve; it should not lie in an area where the
slope is too steep.
Accurate results in the
SET_PH* mode can only be expected when the
sensor used has been previously calibrated correctly.
U[mV]
V[ml]
t[s]
EP
V[ml]
Initial
addition
Continuous
addition
Control
range
SET: endpoint titration
Reagent addition:
controlled addition,
depending on the control
difference
(actual value – endpoint)
Switch-off criterion:
drift-controlled and/or after
waiting period
7.4.1 Measuring mode
An endpoint titration can be carried out with four different types of meas-
urement:
• potentiometric pH measurement ( SET_PH*)
• potentiometric voltage measurement ( SET_U*)
• amperometric measurement with selectable polarization voltage ( SET_UPOL*)
• voltametric measurement with selectable polarization current
(
SET_IPOL*)
7.4.2 Reagent addition
Reagent addition takes place in three different phases. The initial addition
takes place with increasing dosing speed. It begins with the defined 'Min.
Rate' and increases up to the 'Max. Rate'.
Dosing is carried out at the defined 'Max. Rate' until the control range is en-
tered.