TFA, Formic or ???

[fabienco]

I am looking for an alternative for TFA. Formic acid and acetic acid do not give, in most of the molecules I am analysing, a good LC separation.
TFA seems (in my case) to be the best compromise between LC separation and MS detection.
Could somebody help me as well with the question in LC-MS I wrote earlier?
Thank you in advance.

[MG]

Well, there is heptafluorobutyric acid. But I imagine it could have some of the same negative factors as TFA. What is the specific problem with your separation and maybe someone can help further?

[fabienco]

I wanted to find an acid less corrosive for the instrument and which do not suppress ions.
My problem is still that I am not sure that I have 2 co-eluting compounds; the details are in the topic LC-MS below.

[MG]

I meant, what is the problem with your separations when you use formic or acetic acids, that you feel that you must use TFA? Perhaps someone can propose alternate strategies to using TFA.

As to your question in the other thread, if I can think of a good answer, I'll post an answer in that thread.

[chhubert]

TFA does suppress ionisation in API. One way I look for alternative is to try using different polar LC columns such as Waters Polaris C18 column, Thermo Hypercarb column, Phenomenex Synergi Fusion RP column, etc for separation. Another approach is by post column addition of propionic acid (TFA-fix) or in-column addition of propionic acid or acetic acid (see Wilson Z. Shou, et al, J.Chrom B, article in press, 2005) to alleviate the problem of ion suppression by TFA.

[fabienco]

Thank you for your replies.
The problem with using formic or acetic acid is that with certain chemicals I have got huge broad peaks on the LC, or no peak separation (co-elution).TFA gives me good separation with a minimum effort.
I tried different columns and TFA came as the best additive.
Thank you.

[MG]

Without the TFA, do these problem compounds elute in fairly low organic mobile phases (or in 100% aqueous)? If so, HILIC may give better retention and peak shape than reverse phase, and without TFA. This forum has a number of posts on HILIC if you search.

[fishin' addict]

What concentrations of TFA have you used in your mobile phase?

[fabienco]

I always used 0.1% TFA in the mobile phase.
Without TFA (acetic or formic) the retention time of the compound is quite similar than with TFA but the peaks are sometime broad.
Thank you.

[fishin' addict]

Try optimizing the concentration of TFA in your mobile phase.

[fabienco]

You mean using much less. What kind of % did you go to if you used it before.
Thank you.

[fishin' addict]

Use less than 0.1%. I'll typically use formic or acetic at 0.1% and when using TFA (which we rarely need to) will use ~0.05% but the concentration of TFA is empirical. Good luck.

[dcobice]

[quote="fabienco"]You mean using much less. What kind of % did you go to if you used it before.
Thank you.[/

Hi, I worked in a C18 platform with (Meoh/H2O) + 0.1% of TFA and run in LC/ESI/MS and didn t have a great ionization supression before adjust my tuning program.