Metrohm 751 GPD Titrino - Manual (Page 54)

2.6 Parameters, key
751 GPD Titrino
51
Control parameters
Dosing outside the control range:
The dosing rate is given mainly by the
parameter "max.rate".
Optimize the parameters "max.rate"
and "dynamics" together to avoid
overtitration the first time the control
point is reached.
Set "dynamics" such that the
measured value lies inside the control
range during the phase where the
value is kept. Set "dynamics" to e.g.
pH=3, U=180 mV for slow reactions.
You can also make a SET pretitration
to reach the control point. In this case,
"dynamics" of the STAT titration is not
very crucial.
Dosing inside the control range:
Here the dosing rate is given mainly by
the parameter "min.rate".
Rule of thumb for "min.rate" in ul/min
= (expected rate of the reaction in
ul/min)/10.
How to proceed if ...
Problem Possible causes and corrective action
Adherence to the control point is
not good. The measured value
is too high, then too low. "The
controller oscillates".
• Set "max.rate" and possibly also "min.rate" lower.
• Set "dynamics" larger.
• Is the stirring efficiency adequate?
• Arrange electrode and buret tip properly, see page
217.
• Are the tubing lengths kinked?
• Possibly use Exchange Unit with a small cylinder
volume (smaller volume increment per pulse).
Time for reaching the control
point is too long.
• Set "dynamics" smaller.
• Set "min.rate" higher.
• Set "max.rate" higher.
U/mV
V/ml
Control
range
EP
t/s
V/ml