Metrohm 840 PC Control 5.0 / Touch Control - Manual (Page 229)

4 Parameters
PC Control / Touch Control
217
selected minimum rate, the longer it takes until the control point is
reached for the first time.
The following rule of thumb should be considered in order to obtain
as constant a dosing at the control point as possible:
10
L/min in reaction of rate Expected
L/min in rate Min.
μ
= μ
Parameters for the predefined titration rates for STAT
Rate of reaction 50 μL/min 100 μL/min 500 μL/min
Control range
(Dynamics)
1.000 pH
60.0 mV
1.000 pH
60.0 mV
1.000 pH
60.0 mV
Max. rate 0.25 mL/min 0.75 mL/min 2.00 mL/min
STAT
Min. rate 5.00 μL/min 10.00 μL/min 40.00 μL/min
Control range
Control
point
V/mL
t/s
U/mV
V/mL
Fig. 4.10: Reagent addition and control range for STAT
Dosing outside the control range:
Outside the control range the dosing rate is mainly characterized by the
maximum rate . The parameters maximum rate and dynamics should be
optimized together in such a way that the titration does not overshoot
too much when reaching the control point. The control range should be
set so that the measured value remains within this range while it is kept
constant. A slightly larger control range should be defined for slow re-
actions (e. g. pH = 3, U = 180 mV). A SET pretitration is frequently
used to reach the control point before the substrate is added. This
means that the STAT titration can be started with a small variation from
the control point.