Re: Instability of TFA/CH3CN

David A. Schooley (schooley@unr.edu)
Tue, 31 Mar 1998 17:39:30 -0800

At 9:25 PM 3/30/98, chris halkides wrote:
>Hello Everyone:
>
> We are analyzing proteins and peptides by HPLC. I am interested in
>the stabilities of TFA in water and TFA in acetonitrile/water. Does it
>matter if the atmosphere above the solvent bottle is air or nitrogen?

Chris-
Aqueous TFA should be stable indefinitely, but once you add
acetonitrile, the TFA catalyzes side reactions of acetonitrile, such as
addition of water to the nitrile giving acetamide. These impurities absorb
strongly @ 210-220 nm. Accordingly, any solution containing CH3CN+TFA
should be kept no mopre than a week. Aqueous propanol-TFA is worse; the
TFA catalyzes Fisher esterification and you can detect a fruity odor
(propyl trifluoroacetate) after only 1 day. Of course, this ester is also
chromophoric at important wavelengths.

David

David A. Schooley
Dept. of Biochemistry/330
Univ. of Nevada
Reno, NV 89557
schooley@med.unr.edu
tel: (702) 784-4136; fax (702) 784-1419