Metrohm 788 IC Filtration Sample Processor - Manual (Page 117)

4.7 Filtration
788 IC Filtration Sample Processor
109
Finally, the sample matrix and the specifications of the analysis method
determine the time for changing the filtration membrane. From our ex-
perience, suspensions cause membrane clogging earlier than bigger
particles in the sample matrix. The latter should be rinsed across the
membrane surface.
An instruction for changing the filtration membrane is given in section
6.3.4.
4.7.3 Selecting a suitable filtration membrane
It is possible to transfer existing procedures for sample pretreatment to
the ultra-filtration of the 788 IC Filtration Sample Processor. For this
purpose different filtration membranes can be used. Please note that
undesirable results can be obtained although membrane pore sizes are
selected according to known particle sizes of the sample.
Own investigations have shown that filtration results of common filtra-
tion membranes do not always automatically fit to their specified pore
sizes. In the following table some qualitative results of own filtration
tests are given. Aqueous suspensions with silica particles of known
sizes have been filtered on the 788 IC Filtration Sample Processor using
membranes with different nominal pore sizes.
test sample:
silica particles in water
pore size of
filtration membrane 1
result
0.5 %, 5 µm 0.15 µm no breaking-through
0.5 %, 5 µm 3 µm no breaking-through
0.5 %, 5 µm 8 µm no breaking-through
0.5 %, 5 µm 10 µm breaking-through 2
0.5 %, 5 µm 12 µm no breaking-through
0.5 %, 1.5 µm 0.15 µm no breaking-through
0.5 %, 1.5 µm 3 µm breaking-through
(1) Nominal pore size specified by manufacturer.
(2) Except this one, all other filtration membranes are produced by a single
manufacturer.
Due to their low thickness, filtration membranes may provide lower filtra-
tion efficiency compared to filters with the same nominal pore size but
higher thickness. This should be taken into account for selection of a
suitable membrane for online sample pretreatment using the 788 IC Fil-
tration Sample Processor.