Chromatography Forum

Good afternoon,

Does anyone know what the pressure limit is for a Zorbax XDB C8 3.5x4.5x150 column is? Right now we are running at a pressure of 230 bar. I would like to know if this will shorten the life of the column

That should be fine, a modern column like that can handle that.

Surprisingly high backpressure indeed – for this column dimensions anyway. That makes me wonder whether your eluent/s is/are ACN containing or perhaps IPA? If the latter is the case, then maybe it’s not that remarkable to generate such a high backpressure.
Anyway, I don’t think you need to worry about the column – it will survive. I would be more worried about the wellbeing of the system in the long run, unless it’s designed to cope with this relatively high pressure. Some modern systems can deal with up to 1000 bar, so it all depends on the system you’re using.
Apart from all that, I’d investigate the system itself - if I were you. Just remove the column and read the pressure – it should read 0 bar (or very close to that value).
Another problem could be a clogged column. If you have another one of the same brand and type/configuration, it would be informative to check it out as well.
Best Regards

^agreed - the column should be able to run that pressure, no problem. The problem may be should the pressure be that high. If there's a fair amount of THF, IPA or something else that's particularly viscous, then fine. Otherwise, you should check your plate counts at some slightly lower flow rates and see if they go up. If they go up a lot, you may be able to get the same results with a shorter column, running at its optimal flow rate (while saving on time, solvents).

Endcapped columns give a higher back pressure than the non-endcapped. And it seems the lower particle size adds to this.

I would lower the flow rate to 0.6 ml/min and add a column temperature of 30C close enough to the ambient.

Endcapped columns give a higher back pressure than the non-endcapped.

I haven't encountered this, and I'm not sure I understand why it should be true.

Hi Tom,

I am just visualizing that higher endcapping creates a greater ligand/bonding density on the particles which consequently add to the resistance offered by the C8 phase.

And, Eclipse XDB is extra densely bonded.

This is just my picture. It doesn't have any supporing evidence.

The ligand on a packing is about 1 nm thick. The particle is about 5 micron thick. Thus the difference in size between a completely uncoated particle and a fully coated particle is 1 in 5000, or 0.02%. To me that does not seem to be very much, although the FDA may disagree with me