Selection of Buffer solution ???

[vanjas]

My question is what kind of buffer solution will be efficient for seperating bile acids, such as ursodeoxycholic acid, chenodeoxycholic acid, lithocholic acid, cholic acid, deoxycholic acid..., using UV-detector with C18 Column ? I've already tried with phosphate and acetonitrile by gradient method. Am I doing right? Becasuse I found that they have very poor sensitivity at 210nm UV detector.
Any expert's help would be really appriciated. Especillay, detail condition...
Thanks.

[Bill Tindall]

I don't have any experience with these acids but 0.05% phosphoric acid and acetonitrile, detection at 205 nm, works well for many aliphatic acids. In a reversed pahse separation the composition of the buffer is unimportant. The buffer just needs to get the pH low enough to supress dissociation of the acids.