By sibylle on Thursday, February 15, 2001 - 05:53 am:
Is it normal for an analytical guard column to last only for about 400 injections (each about 0.1 mg substance per injection) ?
(It's a 8u, 4.6mm diameter C18 guard column)
By Anonymous on Thursday, February 15, 2001 - 09:46 am:
i think this depends on what you inject.
By H W Mueller on Friday, February 16, 2001 - 12:20 am:
Right! We have finished guard columns and even columns with one injection.
What is your criterium of a used-up guard?
By sibylle on Friday, February 16, 2001 - 06:08 am:
Pressure is increasing within every new day. (I have a semiprep column attached to the same system and there pressure remains constant, so I think I can cross out blockage of seals.)
What other criteria do you know for a used-up guard ? (Except impurities in your spectra that make no sense)
By sibylle on Friday, February 16, 2001 - 06:10 am:
One injection ?!
By H W Mueller on Saturday, February 17, 2001 - 04:11 am:
That´s why I asked about your criteria, because I can only think of pressure problems (usually frit not column bed) as a simple indicator of problems. Another indicator would be to open the pre-column and/or the main column and inspect the filling.
Yes, one injection of plasma/serum of some patients have blocked columns so badly that we had trouble recovering them. Consider this: We had plasma/serum that completely plugged centrifuge micro filters (0.2 µm pores) after only ~1 drop (of 500 µL) went through. Plasma/serum of a normal person filters in less than a minute. Now, 0.2 µm is a huge space even for a protein.
Also: since it is probably the frit, check whether
reversing the precolumn´s flow for a few minutes (off the column!) gets rid of the "dirt".
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