I was wondering if any of you would be kind enough to share her/his experience with me, and would suggest vendors and models for such columns.
I really like "ceramic" hydroxyapatite from Bio-Rad. The only type that behaves in the columns long-term, without the need for repacking. It also gives better resolution and/or allows faster faster flow rates. Their "type I" has higher capacity and generally more useful.
The great thing about hydrohyxapatite is that essentially all proteins bind to it as long as there is no phosphate around even in high salt (like 500 mM NaCl). So it is a great way to concentrate proteins from diluted solutions or a nice chromatography step right after AEX.
Some proteins (generally few, mostly alkaline) will elute at very high NaCl (1-2 M), others with require phosphate. For ceramic hydroxyapatite I find that the useful range is 0-100 mM phosphate at pH ~ 7.0. Capacity of the ceramic hydroxyapatite is lower than the normal mineral form, only around 25 mg/ml.
Dima
