Heptafluorobutyric Acid

[adam]

Hello Chromatographers

I was curious to ask a question today. We just received a reversed phase HPLC method, that uses Heptafluorobutyric Acid as the mobile phase additive. I have been doing HPLC for many years, but I have to admit that I have never come across this acid before.

Can anyone share any insight as far as: what are the unique benefits or limitations of this acid (in comparison to more common options such as Formic Acid, TFA, phosphate buffers, etc).

Any insight would be much appreciated.

Thank You
Adam

[mattmullaney]

Hi Adam,

Heptafluorobutyric acid may be used as an ion-pairing agent in LC-MS separations as it is volatile, as opposed to, say, sodium heptanesulfonate.

[DR]

^ and I think it buffers a different pH range vs TFA and other things mentioned.

[Gerhard Kratz]

Used in the determination of amino acid sequences in proteins. HFBA is a strong acid and an ion-pairing agent that is used in analytical chemistry such as in HPLC and in GC/MS in a similar manner to trifluoroacetic acid. The strong acidity of HFBA ensures that other acidic groups such as carboxylic acid moieties on biomolecules remain protonated, and thus the samples are able to interact with organic solvents in such processes as reverse phase chromatography. The longer alkyl chain of HFBA makes it more hydrophobic than TFA, and thus HFBA can be utilized with more hydrophobic samples.9

That I found on the web. As every ion-pairing Agent it will modify the surface of the packing material that way that the column should be used only for this application.

[juddc]

I've used HFBA many times and have found it to be most handy in conjunction with ELS detection. It is more hydrophobic than TFA, which means that it can be effectively used to retain molecules that are more hydrophilic under reversed phase conditions. For instance, I've had excellent luck using HFPA to separate small, very hydrophilic urea derivatives which contain no chromophore to speak of.

I have not had difficulties with HFBA altering the selectivity of my columns and compared to alkyl sulfonates, I've found re-equilibration to be more rapid for gradient methods, however your mileage may vary on this.