> ----------
> From: Henry Keutmann[SMTP:keutmann@helix.mgh.harvard.edu]
> Sent: Thursday, March 18, 1999 5:32 PM
> To: Recipients of ABRF List
> Subject: Isoelectric peptide purification
>
> To my ABRF colleagues:
> A collaborator has a question regarding the purification of a
> tripeptide at or near its isoelectric point. He purified it by HPLC and
> wants to eliminate all residual TFA, isolating and lyophilizing it at its
> isoelectric point of about 5.3. We should be able to replace the TFA with
> ammonium acetate (perhaps with an intermediate treatment with dilute HCl)
> for ion-exchange (e.g. mono-S) chromatography.
> Firstly, will this effectively remove residual TFA?
> Second, after lyophilization what will be the state of the peptide
> in terms of salt content: will acetate and ammonium remain as counterions
> at the N and C terminus, or is there a way in which they can be removed
> (e.g. replaced by water, or preferably retrieved as the noncomplexed
> peptide)? Would the salt form be detectable on mass spec?
> Thanks for any advice!
> Henry Keutmann
>
> Endocrine Unit, Wellman 501
> Mass. General Hospital
> Boston MA 02114
> 617-726-3966
>
>