Chromatography Forum

Hello,

if I would like to go down to pH 1 - 2 with my mobile phase: what column would you recommend for having a long column-life?

Thank you very much.

Florian

Concerning chemical stability, I've been a fan of the XBridge columns for a long time. The XBridge C18 is not only applicable to high-pH applications but due to its trifunctional bonding also stable at acidic pH (according to Waters down to pH1 - I've never went that far down, though). Be sure to use the XBridge C18 for highly acidic applications, not the XBridge Shield C18 - that one is only monofunctionally bonded and therefore considerably less stable.
Another thing that comes to my mind is THE classic for acidic conditions - Zorbax SB-C18. It employs bulky side-chains for protection against acidolytic cleavage. You may also look at the fancy core-shell version of this, the Poroshell SB-C18.
Another possibility would be some sort of polymeric bonded column, like Purospher STAR or the like.

...and don't forget that classic, old-school, outdated, non-endcapped columns such as Lichrospher can show quite impressive stability under acidic conditions - it's the endcapping of "modern" columns that get's lost first under strongly acidic conditions.

It there any particular reason why do you want to go to pH 1-2?

If I would like to go down to pH 1 - 2 with my mobile phase: what column would you recommend for having a long column-life?

What are your applications? You already have good suggestions for silica based materials.

If you want ultra pH stable non-conventional material you may try Hypercarb column (Thermo, porous graphitic carbon). One can easily boil this material in conc. acids and bases without any effect. Porous graphitic carbon is essentially a reversed phase material with interesting selectivity. Another material is carbon clad zirconia but it is a troublesome stationary phase.

Just keep in mind a very fine problem: Using a very low pH will slowly attack the metal tubing and the frits. It is known that metallic contamination changes retention time for some molecules such as cytosine. Secondly, metallic contamination from frits is said to catalyze degradation of the attached ligands from silica phases.

Regards,

Farooq

Dear all,

thank you very much for your recommendations.

The reason for using a low pH is that my basic compound shows tailing at pH 3.0, a better symmetry at pH 2.5 and I intend to try to gow lower. As the compound has no significant UV absorption, I have to choose a very low wavelength. Thus, I intend to use phosphoric acid with a cut-off < 200 and good buffering capacity between 1.1 and 3.1. Mixed-mode phases I tried need TFA which significantly reduces my signal.

Regards

Florian

And don't forget the polymer based C18 columns.

Along with LiChrosphere and XBridge, I am a big fan of Atlantis T3, another Waters phase.

And, over the years, I've used Zorbax StableBond (also mentioned above) at pH 2 or so with great success.

Please, see what you think, and thank you.

You can use any acid with our mixed-mode (phosphoric, sulfuric, methanesulphonic, perchloric). Your issue is some kind of weak secondary interaction which contributes to the tailing. This can be a chelating interaction with metals. I assume that you have nitrogen based heterocycle or some kind of nitrosamine.

Dear Vlad,

thanks for the acid information. Could you inform me on the UV cut-off of methanephosphonic acid? It might be a good compromise between organic and inorganic acid.

Thank you very much

Florian

all acids I mentioned have 190 nm cut off. In my original post I meant methanesulfonic acid, but you can use pretty much anything (except HCl and HF). If you can send me a structure I might be able to tell you why your peak tails. You also can try an alternative approach - hydrogen-bonding columns (newsletter coming out this week):
http://www.sielc.com/upload2/file/2014% ... SHARC1.pdf (might work for you if your compound is soluble in ACN/MeOH and has ability to form hydrogen bonds.

If your basic solute tails, consider going the opposite direction in pH (alkaline).

Disclaimer-- I work for Hamilton

http://www.hamiltoncompany.com/download ... atures.pdf

Tailing could be reduced significantly by adding some ions to the mobile phase.
Prepare a 0.05M buffer at the same pH you’re using today and see the difference

Or maybe the column’s not good anymore – or has never been (?)

Best regards