Chromatography Forum

Hi
One of my colleague has started using Heptafluorobutyric acid (HFBA) as ion pairing agent for RP-HPLC, I have read somewhere that ion pairing agents tend to sticks to the stationary phase and changes its selectivity (please correct me if I am wrong)…So do HFBA sticks to stationary phase and changes its selectivity (I think TFA doesn’t get stick to the stationary phase) ???
Once a column is used with HFBA as ion pairing agent, can it be used for other ion pairing agents lets say TFA etc…??

Thanks

HFBA will "modify" stationary phase in situ and may interact with analytes with opposite changes. But I would expect you should be wash it out in the most part. But I rememebr hearing people compaining TFA "changes "column. If it is the case, HFBA should behave the same way.
For your second question, the answer is yes. You can use the column with TFA after using it with HFBA.

hi
thanks for the reply,

For your second question, the answer is yes. You can use the column with TFA after using it with HFBA

so i dont have to do any special cleaning or washing of the column after use with HFBA, before shifting to other ion pairing agents..??

also how can one be sure that there are no HFBA remaing in my column (have simillar doubt about other ion pairing agents) ??

Anionic ion-pairing agents are easier to remove compared to cationic ones because the latter strongly interact with (attract) the silanol groups on the surface of the stationary phase while the former repell silanol groups. Still you need to thoroughly wash the column with the TFA containing mobile phase to remove the residual HFBA. Others may have better suggestions on this.

You can monitor the selectivity reproducibility from consecutive injections to determine if the conversion from HFBA to TFA is satisfactory.

So HFBA is not repelled by the negative charges.