Metrohm 899 Coulometer - Manual (Page 40)

4.2 Working with water standards
￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
30 ￭￭￭￭￭￭￭￭
899 Coulometer
6 Pull the piston of the syringe up to the end and swing the syringe
back and forth somewhat.
The inside of the syringe is being rinsed by water standard and freed
from water contamination.
7 Dispose of the used water standard in a waste bottle.
8 Draw the rest of the water standard into the syringe, aspirating as lit-
tle air as possible.
9 Push out any air bubbles that may be present in the syringe.
10 Wipe off the needle with a lint-free paper towel and cover it with the
appropriate cap.
11 Place the syringe on the balance and press [TARA].
12 As soon as the drift on the 899 Coulometer is stable, take the syringe
by hand, press [START] and inject approx. 1 mL of the water stand-
ard through the septum.
There are two possibilities:
13 ￭ Inject the water standard without immersing the needle in the
reagent liquid. If a little drop remains on the end of the needle, it
must be aspirated back before pulling the needle out of the sep-
tum.
The water standard should not be sprayed from the syringe onto
the electrode nor onto the wall of the coulometer cell.
or
￭ Inject the water standard directly under the surface of the reagent
liquid.
Take care to ensure that you do not aspirate any liquid when you
withdraw the syringe out of the reagent liquid.
14 Close the syringe with the same cap and place it back on the bal-
ance.
15 Read off the value displayed by the balance and enter it on the Coul-
ometer as the sample size.