Metrohm 711 Liquino - Manual (Page 39)

3 Introduction
711 Liquino, Instructions for use 33
3.2.7 SMPL – fully automatic sampling
The capabilities and possible uses of an SMPL method will be demonstrat-
ed by means of a complexometric titration of Ni
2+ with the help of the 711
Liquino and Titrino 716.
Chemistry
The Ni 2+ ion is buffered to pH 10, complexed with Cu-EDTA and then titrat-
ed with Na-EDTA. The detection mechanism with the Cu-ISE electrode is
based on the following equilibrium equation:
Cu-EDTA
Cu 2+ + EDTA 2-
The presence of the Ni
2+ ion displaces the equilibrium to the right:
Ni
2+ + Cu-EDTA Cu 2+ + Ni-EDTA
The concentration of the Cu
2+ ion (to which the Cu-ISE electrode reacts)
depends on the stability of the Ni-EDTA complex.
Procedure
The SMPL mode of the Liquino offers a fully automated sample transfer,
perfect preparation of the titration cell between the individual titrations (for
multiple determinations) and complete control of the Titrino. However, a cor-
responding method must first be created or selected in the Titrino.
The Dosino at connection 1 carries out the "sampling“ processes, for which
its four ports have fixed definitions.
1. Through port 1 the Liquino draws in the required amount of sample and
transfers it to the titration vessel through the cylinder and port 2.
2. Solvent is drawn in through port 3 and transferred to the titration vessel
for rinsing/diluting (the amount can be freely selected) – in this case H
2
O
is used.
3. The second Dosino adds the buffer (pH 10).
4. The third Dosino adds the complexing agent Cu-EDTA.
5. 30 s is allowed to elapse (this possibility exists after each reagent addi-
tion) in order to allow the complexing ion to be completely bound and to
release the Cu
2+ ions.
6. The Titrino is started via the remote lead and the sample is titrated with
Na-EDTA.
At the end of the titration the "sampling“ Dosino removes the contents of the
titration vessel through port 2 and transfers them to a waste container via
port 4.