There is no question that a Speedvac or lyophilizer will remove the TFA
adequately from the typical fraction collected from a reversed-phase HPLC
column, where the concentration is typically 0.05-0.1% (at least, adequately
if you're going on to sequencing; not necessarily adequately if your next
step is a bioassay). Dave Schooley was referring to a recently introduced
method where a peptide mixture is adsorbed to a cation-exchange column (weak
or strong) and then eluted with a gradient to @ 10-20% acetic acid. This
elutes the peptides not by displacing them, as salt gradients do, but by
uncharging the stationary phase. It has a number of advantages, which I
won't go into here. The chief disadvantage is the opacity of the mobile
phase below 230 nm. A couple of days ago, Hong Li posted a query about
finding some alternative to acetic acid that was transparent as well as
volatile. a method that will remove 0.1% TFA from a sample may not work as
well with a sample containing 10% TFA. Also, the concentration the peptide's
exposed to may go above 10% during the lyophilization or Speedvac spin,
depending on the composition of the TFA/water azeotrope (assuming one
exists). Dave Schooley was lamenting the lack of data on the existence or
composition of this azeotrope.
Best regards,
Andy Alpert
PolyLC Inc./ Columbia, MD
phone: 410-992-5400 FAX: 410-730-8340 e-mail: POLYLC@aol.com