Metrohm 844 UV/VIS Compact IC - Manual (Page 91)

4.1 Practical notes on ion chromatography
844 UV/VIS Compact IC / Gebrauchsanweisung 8.844.1051
79
Fresh eluents should always be microfiltered (0.45 μm filter) and
degassed (with N
2
, He or vacuum). For alkaline eluents and eluents
with low buffering capacity one should preferably use a CO
2
absorber
(see Section 2.6.3).
The supply vessel containing the eluent must be closed as tightly as
possible to avoid excessive evaporation. This is primarily important with
eluents containing organic solvents (e.g. acetone), the evaporation of
which can lead to drifts in the long term. If work is performed in a very
sensitive range, even if one drop of condensate falls back in the eluent
this can cause a noticeable change in the background conductivity.
Eluent change
When changing the eluent you must make sure that no precipitation
can occur. This means that solutions used in sequence must be
miscible. If the system needs to be rinsed with organic solvents then it
may be necessary to use several solvents with increasing or decreasing
lipophilicity (e.g. water ↔ acetone ↔ chloroform).
4.1.4 Peristaltic pump
The 6.1826.110 Pump tubing used in the peristaltic pump is a
consumable with a limited working life. This is why you should replace
the tubing at regular intervals; when in continuous use this should be
approx. every 4 weeks (see Section 4.2.5).
The working life of the pump tubing depends to a great extent on the
contact pressure, so make sure that this is set correctly according to
the instructions given in Section 2.10.2 and, if the pump is to be
switched off for a longer time, lift up tubing cartridge 96 by fully
loosening snap-action lever 98 on the right-hand side (in this way the
set optimal contact pressure is retained).
The 6.1826.110 Pump tubing is made from PVC and must
therefore not be used for rinsing with solutions containing
organic solvents. In this case you must use different pump
tubing material, or use a different pump for rinsing.
4.1.5 Connections
All connections between injection valve, column and detector must be
as short as possible, have a low dead volume and be absolutely tight.
The PEEK capillary after the detector block must be free from
constriction (the measuring cell is tested to 5 MPa = 50 bar back
pressure).
With the PEEK versions 2.844.0010, 2.844.0020, 2.844.0110 and
2.844.0120 only PEEK capillaries are used in the high pressure area.
Use PEEK capillaries with 0.25 mm i.d. for the capillary connection bet-
ween injection valve 46 and UV/VIS detector 43.
With the Steel versions 2.844.0030 and 2.844.0130 only Steel
capillaries are used in the high pressure area.