Metrohm 750 Autosampler - Manual (Page 43)

4 Notes – Maintenance – Faults
750 Autosampler
40
A further possible way of filtering samples is by means of the optional
6.2743.030 filter stoppers. These filter stoppers, which contain a
built-in filter unit, are fitted to the sample vials just like normal stoppers.
The way they work is shown in Fig. 10.
Fig. 10: Sample filtering with FilterCaps
FilterCaps  were designed to free the chromatographer from the time-
consuming task of hand filtering samples. They can be used to free
samples from suspensions and particles. However, filter stoppers are
not suitable for filtering samples containing a large amount of solids as
this causes the filter to become blocked which also blocks the transfer
needle. Those samples which are difficult to filter manually with a mem-
brane filter (see Fig. 9) should be centrifuged before filtration.
When working with filter stoppers the " POS4 " setting for the needle
immersion depth " Needle Depth " must not be selected.
4.1.3 Operating parameters
Before samples can be injected all necessary instrument settings must
be made. The most important parameter is the retention time. The time
interval "
Run Time
" between individual injections must be sufficiently
long so that all substances are eluted before the next sample is in-
jected. Moreover, it may be necessary to include further time for base-
line analysis and evaluation with the evaluation system.
Filtered sample
Unfiltered sample
To injection valve