Metrohm 761 SD Compact IC - Manual (Page 97)

6.1 Practical notes on ion chromatography
761 SD Compact IC / Instructions for Use 8. 761.1043
89
Maintenance
An unstable baseline (pulsation and flow rate fluctuations) is attributable
to contaminated valves or defective, leaking piston seals in many
cases.
Contaminated valves are cleaned by rinsing with water, RBS solution
or acetone (see Section 6.2.5). When the cleaned valves are reinstalled,
you must ensure that the flow direction is correct.
The procedure for replacement of piston seals is described in Sec-
tion 6.2.5.
Salt crystals between the piston and the seal are the cause of abrasive
particles which can contaminate the eluent. These lead to contaminated
valves, pressure rise and, in extreme cases, to scratched pistons. It is
thus essential to ensure that no precipitates can occur.
6.1.3 Eluents
The eluent for determining soft drinks is pre-prepared and packed in
MPaks. If you wish to use your own eluents, please follow the conven-
tional rules for eluent handling for IC.
6.1.4 Peristaltic pump
The pump tubing used by the peristaltic pump is consumable material
with a limited lifetime and should be exchanged at regular intervals
(approx. every 4 weeks under continuous use; see Section 6.2.9).
The working life of pump tubing depends to a considerable extent on
contact pressure. This is why the contact pressure must be correctly set
as described in Section 2.14 and the tubing cartridges 57 must be fully
raised by releasing the snap-action lever 59 on the right-hand side if the
pump is to remain switched off for a lengthy period of time (this means
that the optimum contact pressure, once set, remains unchanged).
6.1.5 Suppressor module
Protection
To avoid contamination of the suppressor module by foreign particles
or bacterial growth, the two filter units PEEK 56 (6.2821.120) must be
fitted upstream of the suppressor module’s inlet capillaries (see Section
2.3.3).
Operation
The Metrohm Suppressor Module MSM consists of a total of 3 sup-
pressor units which are in turn used for suppression, regenerated with
sulphuric acid and rinsed with back-flowing eluent. In order to record
every new chromatogram under comparable conditions, work is nor-
mally carried out with freshly regenerated suppressor. Switchover oc-
curs automatically together with valve switchover to Fill .
The suppressor units must never be regenerated (with H
2
SO
4
) in the
same flow direction used for the eluent.