Chromatography Forum

I switched to a Beckman Prep HPLC by changing the pump, detector and ... The column size is 19*150mm.

The problem I have is the pump head pressure exceed limit, which is 2.5KPSI. The flow rate is 15ml/min. This prep pump should be able to run up to 30ml/min.

I would like to get the suggestion from you experts.

Thanks a lot.

What column are you using and what is your system back pressure (without column) at 15mL/min?
Is 2500psi the maximum this pump can handle or can you change this pressure limit on the pump? I have no experience with Beckman prep pumps.

I'm using a XBridge C18, 5µm, 19x100mm and get a backpressure of about 1700 psi @15 ml/min if I had it correct in mind.
So the pressure for a 19x150 mm I would expect is about 2500 psi @15ml/min.

Maybe there's a possibility to change the pressure limit so you can set a higher one. Even with this, I think you won't be able to run your colum @30ml/min.
But keep in mind, that you'll lose some performance at flow rates too high. 15 ml/min @19mm will turn to about 0.9ml/min @4.6mm column, which is near the optimum of the VanDeemter curve (for 5µm particles).
Maybe this could turn into a higher loadability (:?: )

Thank you.

I am using a 5 um waters Atlantis column, 19*150. The pump head pressure is 0.8KPSI without the column at 15ml/min.

It looks that the limit (2.5KPSI) can not be changed.

It is not uncommon that pumps for preparative chromatography have pressure limits. The primary approach around this problem is to reduce the flow rate, which of course increases the run time. The second approach is to use shorter columns for the prep runs. I am generally recommending columns with a length of 5 cm for preparative chromatography. Unfortunately, this is not going to help you now, but it may be relevant for your next purchase.

Your pressure of 800psi without a column seems quite high. Does your pressure read 0 (or close to) with no flow? Your pressure transducer might need adjusting if not. If the pressure is real then try removing the detector cell and watch the pressure, then try a piece of tubing and so on until you find where the pressure build up is.

Another question, You changed the pump/detector... but did you use larger ID tubing in plumbing this? analytical ID tubing at that flow can cause large packpressures.

Also, what kind of mobile phases are you using. I routinely use a 19*100mm 5um column at 20mL/min with backpressures less than 1500 PSI in acetonitrile/water solvents, but methanol water can be much higher.