Waters xbridge c18 and Agilent Extend c18

[bloodstone001]

Hi, everyone. Does any one has the experience of using Xbridge c18 and Agilent Extend c18? How about their lifetime under basic phosphate buffer and high temperature around 55 degree?

[Uwe Neue]

I assume that you are talking about pH 12? The XBridge column lasts for 250 hours at pH 12 and 30 degrees. I usually calculate that the lifetime decreases by about a factor 3 for every 10 degrees.

I do not think that the Extend column will get anything close to this, since it is based on silica, and it is the silica that is dissolving. Even other phases that claim to have a good stability in the alkaline pH range lasted for only 10 hours under the same conditions. I bet a silica-based column may last for maybe 3 hours, if at all....

[Bruce Hamilton]

The Agilent site notes that temperature limits are 60°C up to pH 8, 40°C for pH 8 - 11.5 for the Extend C18 column.

I wouldn't spend money buying a column like that for the region you want to work in, as you're well outside the design window. You will see degraded performance almost every time you use it till it dies prematurely.

Join the " be kind to columns " crowd, and keep having fun,

Bruce Hamilton

[bloodstone001]

Thanks!
My separation pH is only 8.9, but the temperature is 60 degree. So I am very nervous about that.

the lifetime decreases by about a factor 3 for every 10 degrees

I'm not quite sure what the word "factor" means.

[Uwe Neue]

You can use XBridge under your conditions without trouble.

What I meant to say is that if a column lasts at pH 12 and 30 degrees for 250 hours, I expect it to last some 80 hours at 40 degrees and some 30 hours at 50 degrees.

But note that this is only true for pH 12. At the pH at which you are working, the XBridge column will last as long as a normal column at pH 5. I am more concerned that phosphate is not a good buffer at this pH, and I would recommend something different. Are you using UV? If yes, at what wavelength?

[bloodstone001]

Thank Uwe Neue very much! I use UV detector at 210nm.This method comes from PHARMEUROPA 17.1. So I assume that it is not easy to change the phosphate buffer.

[Uwe Neue]

What is the counterion in the phosphate buffer? If it is ammonia, this is good, since the pK of ammonia is 9.25, and you are right at the pK of the ammonium buffer (then your buffer is not a phosphate buffer, but an ammonium buffer with phospate as the counterion).