Metrohm 865 Dosimat plus - Manual (Page 64)

6.4 Pipetting and diluting (LQT) ￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
54 ￭￭￭￭￭￭￭￭ 865 Dosimat plus
6.4 Pipetting and diluting (LQT)
6.4.1 General description
Usage
The dosing mode LQT (liquid transfer) is suitable for the pipetting and
diluting of liquids. The set parameters can be saved as a method and then
later used where required.
Pipetting
Pipetting is the transferring of a particular volume of a sample from one
vessel to another. The sample is aspirated into a tubing for this purpose,
without the sample actually entering the dosing cylinder. A "hydraulic liq-
uid" is required in the exchange unit for the aspiration and expelling of the
sample. In normal cases, this is degassed, pure water.
An air bubble (air gap or separating bubble) at least 0.5 cm in length must
be located between the sample and the hydraulic liquid in order to pre-
vent any mixing of the two liquids.
Because of the fact that the tip of the pipetting tubing is moved during
the entire procedure, an additional air bubble may be aspirated into the
tip after the sample has been aspirated. This prevents the sample from
being able to drip out of the tubing.
Exchange units with 1 mL to 5 mL dosing cylinders and a 10 mL pipetting
tubing (6.1562.100) or a 2 mL pipetting tubing (6.1562.110) are suitable
for the pipetting.
Diluting
The diluting of a sample involves the pipetting of a sample (see above)
with subsequent rinsing of the tubing, which simultaneously causes the
sample to be diluted. The solvent that is to be used for dilution is there-
fore used in the exchange unit as the "hydraulic liquid".
The air gap between sample and hydraulic liquid, and the air bubble at the
tip (safety air gap) are also recommended during dilutions.
Exchange units with 10 mL to 20 mL dosing cylinders and a 10 mL pipet-
ting tubing (6.1562.140) are suitable for performing the dilution.
Performing a pipetting or dilution
We recommend using the Manual Dosing Controller.
The pipetting proceeds semi-automatically in several stages after the [GO]
key is pressed. Each subsequent step in the run is started by pressing the
[GO] key on the Manual Dosing Controller.