high column pressure

[moon704520]

I have been using kromasil c-18 columns for a long time ,yet i find that my column pressure is too high,(if replace this cloumn with other one,the pressire will decrease to the normal level),what I want to know is how to
clean the column to reach the normal pressure?

[SMC]

Hi,

The manufacturer should provide information about that.

Generally I would say if a column is used for a while &/or does not perform as well as it did initially I would use something like the following procedure:
> flush with water:organic 5/95 v/v (for very hydrophilic compounds)
> gradient up to water:organic 50/50 v/v (organic can be higher since no buffer is used)
> flush with water:organic 50/50 v/v (for hydrophobic compounds).
> repeat if necessary.

In addition: If your column is blocked it has most likely happened at the column head.
If there is no rescue for this column try the same procedure with the column turned the other way round.

I am not sure whether you can open the column at the head and replace the first part of the packing (and the void volume .

You have not said anything about the performance yet of your Kromasil?

[DR]

It has been my experience that certain columns build up back pressure at faster rates than others and that there is prettu much nothing short of opening them to alleviate this (assuming that you're injecting fairly clean samples). I don't open them as it is not worth the time and effort given the low chance of long term success.

I have not had particular problems with Kromasil packings, but I have noticed that Metachem ODS columns tend to increase in back pressure faster than equivalent Phenomenex (Prodigy) columns, all other things being equal, for a couple of sample types that I encounter.

I suspect that the better the initial packing process is, the more resistence to further packing a column will have. Columns that are not packed as well may experience density changes in the bed over time, resulting in increased back pressure.