Metrohm 833 IC Liquid Handling Unit - Manual (Page 83)

8.4 Filtration
833 IC Liquid Handling Unit / Instructions for Use 8.833.1003
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stable rate for many samples and then drop sharply, with a different
sample matrix it may diminish slowly and continuously.
The time when the filter membrane should be replaced ultimately
depends on the sample matrix and the specifications of the analytical
method used. In our experience very fine and suspended particles in
the sample matrix will block the filter membrane more rapidly than
coarse particles, which tend to be carried past the membrane in the
sample flow.
Instructions for replacing the filter membrane are given in
Section 9.2.8.1.
8.4.3 Filter membrane selection
You can apply existing sample preparation rules to filtration with the 833
IC Liquid Handling Ultrafiltration Unit. If you wish to use a different filter
membrane from that supplied as standard then please note that, even if
the particle size is known, the selection of a membrane with an
appropriate pore size does not automatically produce the required
results.
Some investigations have shown that the retention capability of normal
filter membranes does not always correspond to their specified pore
size. The following table shows the qualitative filtering effect of filter
membranes with different nominal pore sizes. The tests were carried
out on aqueous solutions containing silica particles with particles sizes
1.5 µm and 5 µm.
Test solutions:
silica particles in water
Pore size
of filter membrane 1
Effect
0.5%, 5 µm 0.15 µm no breakthrough
0.5%, 5 µm 3 µm no breakthrough
0.5%, 5 µm 8 µm no breakthrough
0.5%, 5 µm 10 µm breakthrough 2
0.5%, 5 µm 12 µm no breakthrough
0.5%, 1.5 µm 0.15 µm no breakthrough
0.5%, 1.5 µm 3 µm breakthrough
(1) Nominal pore size according to information supplied by manufacturer.
(2) All the membranes came from a single manufacturer except this one.
Please also note that, because of their lack of thickness, the retention
capability of filter membranes may be lower than that of thicker filters
with the same nominal pore size. This should be taken into account
when choosing a suitable filter membrane.