Metrohm 789 Robotic Sample Processor XL - Manual (Page 115)

3.8 Dosing and liquid handling
Metrohm Sample Processor, Operation 107
Formation of separating bubble (air gap)
11
Command sequence:
LIFT: 1 : shift mm
DOS: 1.1 : -0.5 mL
In order to prevent the carrier liquid and
sample solution from mixing a separating
bubble, must be formed that occupies a
length of at least 5 mm in the pipetting
tubing. However, the separating bubble
must also be measured out with sufficient
accuracy. This is why a Dosing unit with
max. 20 mL cylinder capacity should be
used for pipetting.
Move to sample
Command sequence:
MOVE: 1 : sample
LIFT: 1 : work mm
The (dissolved or liquid) samples can be
contained in open beakers on the rack or
in sealed vials. In the latter case instead
of the pipetting tubing a suitable injec-
tion needle should be connected to Dos-
ino Port 1 with a normal piece of tubing
(2 mm dia.).
Aspirate sample
11
Command sequence:
DOS: 1.1 : -5.0 mL
WAIT: pause 3 s
LIFT: 1 : shift mm
DOS: 1.1 : -0.2 mL
Aspiration of the sample should be car-
ried out at a reduced filling rate
(<10 mL/min). The appropriate setting
can be made under >Dosing
unit def.
With non-aqueous samples an additional
small air bubble may be drawn into the
pipetting tip in order to prevent the sam-
ple solution from dripping.
Move to target
222
Before the pipetting tubing
containing the measured
out sample is moved, the
corresponding Dosino port
must be closed.
Command sequence:
DOS: 1.2 : port mL
MOVE 1 : ext.1
LIFT: 1 : work mm
The titration cell should
be filled with solvent
before the sample is
added so that the
sample can be pipet-
ted directly into the liq-
uid (tip immersed).