Zwitterionic buffers and strong ion exchangers?

Dan Diaz bl275 at cleveland.Freenet.Edu
Wed May 26 20:35:42 EST 1993


In a previous article, C741SCB at SEMOVM.SEMO.EDU (C741SCB) says:

>Does anybody know anything about the interaction between zwitterionic
>buffer systems and Q ion exchange resins? I am in the middle of
>a protein purification that looks as if the next logical step involves
>an anion exchanger equilibrated at below pH 7. For obvious reasons
>I don't particularlywant to use a buffer system that will interact
>with the column. I suspect that a zwitterionic system would pose less
>of a problem as far as competition between the buffer and the proteins
>of interest than say phosphate or acetate, but I haven't seen anything
>in the literature dealing with this.
>

You should definitely avoid the use of phosphate, acetate, or any other
anionic buffer with anion exchangers such as Q or DEAE.  Zwitterionic
buffers (like the Good buffers) are fine provided you use them within their
buffering range at a strength of 50 mM or so.  I dont understand why you
mention that running an anion exchanger at pH <7 is indicated.  Most of my
colleagues and I run strong and weak anion exchangers (such as Q or DEAE) in
either Tris or MOPS at pH 7.4 or higher.  S, CM, or Heparin (cation
exchangers) we typically run in phosphate or MOPS at neutral pH or below.

Pharmacia's booklet on Ion exchange on FPLC contains a lot of information
useful for all types of chromatography, including recommended buffers for
given resins at particular pH ranges.
-- 
Dan Diaz
bl275 at cleveland.freenet.edu



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