Re: volatile ion exch. mobile phase
David A. Schooley (schooley@med.unr.edu)
Fri, 12 Sep 1997 13:07:32 -0700 (PDT)
Bill-
I did not mean to say that TFA in CH3CN:H2O mixtures does not
evaporate on COMPLETE evaporation, what happens is that if you do a
PARTIAL evaporation (say, intending to remove the CH3CN selectively
leaving you with predominantly aqueous solution) and then titrate the
predominantly aqueous solution, you will find that the concentration of
TFA has INCREASED. This is strongly suggestive of formation of an
azeotrope, as TFA boils at 72 deg if memory serves me correctly. HCl is a
gas yet forms an azeotrope with water boiling at 110.
However, if you have ammonia or an organic amine in there, you
get an ammmonium (or alkyl ammonium) trifluoroacetate salt which is as
non-volatile as ammonium chloride.
On Fri, 12 Sep 1997, Bill wrote:
> David A. Schooley noted:
>
> > TFA must
> >also form a high-boiling azeotrope with water as 0.1% TFA becomes more
> >concentrated as you evaporate it, as noted earlier today by Andy Alpert.
>
> I would like to know more about this idea, because the experience of some
> colleagues points toward TFA (0.05% - 0.2%) "evaporating" from ACN:H2O
> mixes. Are both a possibility, or is there some study that can clarify this
> issue?
>
> Bill Chestnut
> Pharmaceutical Sciences
> Campbell University
> Buies Creek NC
>
>