FPLC Air gap

[saraswathi]

Hi,
I am using Amersham's pre-packed Superdex 200 column and their FPLC system.The problem is, whenever I run the column, a gap begins to develop at the top and the column seems to start compressing.When I run the column inverted,the matrix is restored to normalcy.I have washed the column with 20%ethanol to remove any particulate matter stuck inside,but didn't see anything come out in the UV.This keeps happening and leads to an increasingly high back pressure.
Any suggestions please?
Saraswathi

[Mattias]

I have used the same column and it is very important that you don't introduce any air in the column. I usually pump without the column for a while to be sure that there is no bubbles coming out, then I run the column backwards for a minute (to eliminate the air in the inlet capillary).

I could also be that the pressure is too high, which that makes the column collapse. Either the flow is too high or you have injected particles.

hope it helps!

[saraswathi]

thanx.Will try.