Chromatography Forum

Hi!

I'm developing a API method that finally should be an HPLC-UV method. For impurity determination/positioning I also need to use MS, but I only have an UPLC-MS for that.
The column I'm using has 400 bar pressure limit and the current method is working around 250 bar in HPLC. As the UPLC gives higher system pressure than HPLC the pressure will go over 400 bar when I set the same method up in UPLC-MS (around 450 bar).
Does the system pressure affect the pressure in the column also or is the pressure lower in the column than the pressure in the whole system?

Thanks in advance

Hi!

I'm developing a API method that finally should be an HPLC-UV method. For impurity determination/positioning I also need to use MS, but I only have an UPLC-MS for that.
The column I'm using has 400 bar pressure limit and the current method is working around 250 bar in HPLC. As the UPLC gives higher system pressure than HPLC the pressure will go over 400 bar when I set the same method up in UPLC-MS (around 450 bar).
Does the system pressure affect the pressure in the column also or is the pressure lower in the column than the pressure in the whole system?

Thanks in advance

Pressure in the system is roughly speaking only flow and column related. In other words pressure builds up in front of the column as the effect of mobile phase flow and you control the flow not the pressure.

Well I guess it depends what is the diameter of tubing also where the flow is going through. I thought that the higher pressure in UPLC is coming from that, because using bypass the pressure is 150-200 bar. Also using the same temperature and flow rate as with HPLC I get the same amount of higher pressure in UPLC. I thought this was normal or is there something wrong with the system?

My question was if this can damage the column or is the pressure in the column lower by the pressure from the system and therefore ok to use?

...is the pressure in the column lower by the pressure from the system and therefore ok to use?

Total pressure will be a sum of pressure built up on the column and a pressure built up in tubing from pump to the column.

...is the pressure in the column lower by the pressure from the system and therefore ok to use?

Total pressure will be a sum of pressure built up on the column and a pressure built up in tubing from pump to the column.

So am I correct thinking that the pressure in column is Total pressure - pressure from tubing? Therefore for example pressure in column would be 450-150=300 bar and a column with 400 bar limit would be ok to use.

So am I correct thinking that the pressure in column is Total pressure - pressure from tubing? Therefore for example pressure in column would be 450-150=300 bar

Yes.

and a column with 400 bar limit would be ok to use.

I think so

Thanks alot!

... because using bypass the pressure is 150-200 bar. ...

To be on safer side I would check the pressure simply with column removed without any bypasses. Have a small beaker to collect mobile phase from the open tubing.

Just as an addition, there is no "magical pressure limit" which defines the stability of a column. The column is not "stable" and 350 bar and will die a quick death at 450 bar.
Generally, column life time will decrease with higher pressures. So, even at 350 bars, it probably will die sooner as if you use it at 250 bar.

According to my experience and given all the possibilities which may lead to a dead column, nominal overpressure would be my last concern - at least with a moderatly modern column which has a good, stable column bed. AFAIK during production, the column is packed at much higher pressures, rather 600+ bar (yes, even the "400 bar columns").
As a side note, I have successfully used a "400 bar column" at a backpressure of ~480 bar without any problems (so far ~1500 injections and going...). Time was limited, so I ramped up the flow-rate .

Well I guess it depends what is the diameter of tubing also where the flow is going through. I thought that the higher pressure in UPLC is coming from that, because using bypass the pressure is 150-200 bar. Also using the same temperature and flow rate as with HPLC I get the same amount of higher pressure in UPLC. I thought this was normal or is there something wrong with the system?

My question was if this can damage the column or is the pressure in the column lower by the pressure from the system and therefore ok to use?

150-200 bar for an UPLC system without column seems a bit much to me. What eluent and flow rate are you working at producing that much pressure?
Try to find out where the pressure builds up, and make sure that it is not after the UV flow cell. Even for UPLCs the flow cells are most often only rated 70 bar.

Also - if you're running the same column with the same flow rate on two different systems, the column should be seeing the same pressure on either system and it should be delivering very similar results.