Steve Mitchell
At 11:09 AM 9/12/97 -0400, you wrote:
>Dear Bill,
>
>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
>
>
>