Chromatography Forum

I would like to know what is the most popular buffer at pH=11 for HPLC. Any data for Gemini HPLC columns (lifetime and stability at pH=11). I know that Xterra Series have good for high pH, but l am looking conditions for pH=11 and more silica-based HPLC column (not hybride)
Thanks

I have used the Gemini columns for a gradient separation with 0.1% ammonium hydroxide in water and 0.1% ammonium hydroxide in acetonitrile as mobile phase components for the gradient separation. The column temperature was 40 C. We used the same set of columns for method development, validation, and sample testing for over 3 years with no significant change in the separation. A typical sample analysis run would consist of over 75 injections of standards and samples. At the end of each analysis before shutting the system down, the column was flushed with acetonitrile to remove the ammonium hydroxide.

Below is durability data for Cadenza CW-C18 (pH 11):
http://www.imtaktusa.com/site_media/fil ... TI418E.pdf

Lot of people tried TEA or organic buffer for high pH (11-12). I used phosphate buffer at the latter pKa (pH=11). I appreciate to know if that buffer (inorganic buffer) is too agressive for higer pH or not. I know Agilent with Zorbax never used this type of buffer. Thanks for your help.

Silica has different elution properties than non-silica (ex: hybrid, zirconia, polymer particle, ect.)
So, we recommend CW-C18 at high pH (organic buffer) only when the above columns fail to resolve the issue.

I don't think anyone recommends using phosphates at pH 11 with silica-based columns

Thanks Bryan,

Do you an idea which buffer is the best for pH=10, 11 using silica-based HPLC columns

The lifetime of silica-based columns at alkaline pH is very short. Different packings behave differently, but all are over an order of magnitude less stable than hybrid columns. Lifetimes of silica columns at pH 11 is in the order of hours, max days, depending on the buffer.

Uwe
Based on your experience, which buffer at pH=11 is less agressive with silica based C18 packing
Thanks

Single amines tend to have pKas around 9 to 10. You need a diamine to get to pH 11 with some reasonable buffering capability.

Thanks Uwe
Charles

Any thoughts on why phosphate is more agressive?
The first thought that jumps into mind is that a pH of 11 in water is just that (hydronium activity of 10^-11). But certainly the ionic strength is different (unless salts are added) when amines are used instead of phosphate. Also some reactions go via specific and others via general acid catalysis. Furthermore, I seem to have read that Na+ as counter ion renders the phospahate buffer more agressive (regarding silica) than if it is K+.

"I know that Xterra Series have good for high pH, but l am looking conditions for pH=11 and more silica-based HPLC column (not hybride)

XBridge are better than Xterra when it comes to durability in high pH
Phosphate at high pH is not reccomended for XTerra iwhereas there is no against when it comes to using XBridge
Pyrridine is nice additive for high pH mobile phase (around 11 I think) and for example ACE columns (silica type) are said to work fine with pyridine for some time but I personally havent tried them for long in high pH cos I usually chose XBridge

Any thoughts on why phosphate is more agressive?
The first thought that jumps into mind is that a pH of 11 in water is just that (hydronium activity of 10^-11). But certainly the ionic strength is different (unless salts are added) when amines are used instead of phosphate. Also some reactions go via specific and others via general acid catalysis. Furthermore, I seem to have read that Na+ as counter ion renders the phospahate buffer more agressive (regarding silica) than if it is K+.

I found this article:

Explanation for the enhanced dissolution of silica column packing in high pH
phosphate and carbonate buffers.
G.W. Tindall. and R.L. Perry
Journal of Chromatography A, Vol 988, Issue 2, Feb 2003.

Thanks so much Bryan
Charles