Metrohm 789 Robotic Sample Processor XL - Manual (Page 113)

3.8 Dosing and liquid handling
Metrohm Sample Processor, Operation 105
3.8.6 Pipetting equipment
Together with an 700/800 Dosino as dosing drive (or "pipetting pump"),
the Sample Processor is exceedingly suitable for pipetting liquids in a
volume range from 0.1 to 10 mL.
Equipment required
• Sample Processor with 786 Swing Head
• Robotic arm with transfer head (e.g. 6.1462.030 or 6.1462.040)
• 800 Dosino with 2 mL, 5 mL, 10 or 20 mL Dosing unit
• Pipetting tubing 6.1562.020 (3 mL) or 6.1562.100 (10 mL) with
drawn out tip
• Any sample rack
• Possibly Stand Support 6.2001.070 with titration cell
3.8.7 Pipetting procedure
Basic principles
Measuring out the liquid to be pipetted takes place in a pipetting tubing
filled with a carrier liquid (preferably water). In order to prevent any
carryover or mixing an air bubble (air gap) must be inserted between
the sample and the carrier liquid. The tubing tip should be drawn out by
hand to form a fine point.
A Dosino drive is used to transfer the liquids into the pipetting tubing.
The pipetting tubing is connected to Port 1 of the Dosing unit. The Dos-
ing unit is mounted on a reagent bottle containing the carrier liquid. This
can be refilled via filling port 2 of the Dosing unit. The carrier liquid can
also be used for rinsing and diluting the sample.
Various pipetting procedures are possible. The following conditions
must always be observed:
• The sample must always be measured out in the pipetting tubing; it
must never enter the Dosing unit cylinder.
• The sample should always be aspirated after the dosing cylinder
has been ejected.
• The difference in level between the surface of the sample liquid and
that of the carrier liquid in the cylinder should be as small as possi-
ble.
• Aqueous sample solutions can be pipetted without having to rinse
the tubing. Non-aqueous samples require the pipetting tubing to be
rinsed with carrier liquid (same solvent as the sample), to avoid
carryover.