Could anybody out there tell me what a borate buffer is? And how to prepare. I heard borate buffer is good for high pH but people just call it "borate buffer"?! I am new to high pH RP chromatography, don't know what chemicals do I need to order. Thank you all.

The molecular structure of boric acid is B(OH)3. The borate ion is B(OH)4-. I have used Potassium Tetraborate Tetrahydrate which is available commercially. The borate ion has a pKa of 9.2 . Other organic buffers such as Tris (tris[hydroxymethyl]aminomethane)are also recommended for high pH applications.

Thanks Don. But Potassium Tetraborate Tetrahydrate "sounds" like an inorganic buffer than organic. I heard that in high pH applications, organic buffer is better than inorganic. What's your opinion?

Secondly, if I am to prepare a 20mM borate or Tris buffer, do I need to adjust pH to within +- 1 pKa? Or what's the pH of the solution before any pH adjustment? If it needs pH adjustment, what do you use? I just need to know what chemicals that I need to order. Thanks.

Sorry, I didn't intend to imply that Potassium Tetraborate was organic. I prepare my borate buffer at a concentration of 10mM and the pH is roughly 9. To increase pH, add Sodium Hydroxide. To decrease pH, I would recommend acetic acid. And yes, I would advise working within 1 pH unit of the pKa. I haven't used organic buffers yet. I previously mentioned an organic buffer (Tris). Some columns are better suited for high pH applications. If you have already chosen a column, you may want to consult the manufacturer for recommendations regarding its pH limitations.

Thanks again for the info. So far I found two columns that manufacturer claimed to sustain high pH: Zorbax Extend C18 and Phenomenex Luna series. Any experience with those? Or any suggestions?

Waters XTerra is one I've had good results with up to pH 12.

ZirChrom's PBD and CARB columns work well with high pH mobile phases.

ThermoHypersil-Keystone produce a Porous Graphitic Carbon (PGC) media known as Hypercarb which can tolerate both extremes of pH even at elevated temperatures.

The Zorbax Extend-C18 shows excellent lifetime at high pH, up to 11.5. Do not use carbonate or phosphate buffers, which accelerate silica dissolution.