Do I NEED the TFA in my mobile phase B??

[mikea]

In my own error, I was switching mobile phases on my system and changed my mobile phase A (0.05%TFA) but forgot to change my MP B, which was 100% ACN (no TFA). Naturally the baseline in my gradient is perfectly flat...which leads me to my question:

Is it absolutely necessary to have the TFA in MP B at all, even at a reduced % (say in my case 0.03%). Is it present in terms of faster pH equilibration or more reproducible retention, etc?

Thanks for your input.

[Kostas Petritis]

The benefit of faster re-equilibration by using TFA in mobile phase B is pretty small (i.e. due to the small hydrophobicity of TFA your column will be equilibrated at about the same time with or without TFA in mobile phase B). Under certain circomstances you can get better base line by using TFA in mobile phase B but if this is not your problem and you still achieve separation of your analytes, you do not need TFA in mobile phase B...

As a bonus, you will avoid ACN polymerization which takes place in acidic pH...

[Rob Burgess]

Have to re-iterate what Kostas has said here - if your separation (peak spacing / retention) is unaffected by leaving TFA out of Pot B then go ahead and use in that way (make sure you change your method).

We have had similar experiences at our company and leaving TFA out of B for gradient runs has resulted in much flatter baselines and hence much better integration of minor impurity peaks - food for thought definitely.