TFA, HFBA stability

[pipettemonkey]

We do not have 1 mL ampules of TFA or HFBA, only larger volume bottles.

In Snyder's new book (High Performance Gradient..), he mentions something about TFA decomposing when exposed to air (and that over-laying the stock with N2 doesn't help).

What "happens" to the TFA, and can it be removed of these impurities by simple distillation? If so, how long before I should re-distill TFA?

As for HFBA- Even freshly distilled HFBA gave unstable baseline. Is this something inherent to HFBA, or due to impurity?

[juddc]

I'll leave the precise details of HFBA / TFA degradation chemistry to others, but I've found a few things about working with HFBA that I thought I'd share. First, remember that it's an IP agent and you need to equilibrate those somewhat longer - usually a good deal longer - than non-IP containing mobile phases. In my experience, it doesn't require as much time as an alkyl sulfonate, but you need to be somewhat patient. Second, if working with a UV detector, I try to limit HFBA use to separating compounds with chromophores that absorb outside the low UV range. Also, I find that HFBA is very handy for use with an ELSD...again depending upon the compound, of course. I would recommend getting TFA ampules - I do this and it keeps things simple. My HFBA is in a larger bottle and I've not had problems related to HFBA degradation, but I'm pretty conservative with it and try to keep my methods sufficiently rugged in order to be run well despite some degradation of the HFBA.

[Chromatographer2010]

I have had major issues in the past with TFA supplied in large bottles. I did looks at the contamination peaks with a unit mass resolution mass spec with .03vol% TFA in the water and ACN. I was unable to get any negative ion peaks(due to ion suppression of the TFA and the massive amount of background) on my mass spec but I did get peaks with masses 279, 372, 292, 574, 655, and 816 in positive ion mode. Also just as a warning it takes forever to get the TFA back out of the system.

This happened with brand new TFA as delivered from the supplier. I did try passing my solvents through a reversed-phase solid phase extraction device that could handle the acid and that helped a lot but not 100%.

I suspect that distillation would also help but seems excessive since its much easier to buy clean chemicals.

I agree with juddc that the TFA in ampules is the easiest solution. I now use the TFA delivered in 1 ml quantities in glass ampules and these peaks have disappeared. I have to change my solvents about every two days or peaks start appearing again.

I have also had ghost peaks in my water and ACN that only show up when there is TFA in the mobile phase so its not always the TFA. Swapping the water or ACN source fixes this problem.

You can also get wavy baselines from both TFA and HFBA which is a magnification of compositional variations from your HPLC pump. The TFA noise typically looks like waves or the occasional blip with a rise and fall or a fall and rise shape. You can usually correlate this noise with the pump stroke or pressure pulsations. The HFBA also has the same shape but the rise and fall or fall and rise are seperated in time depending on the organic concentration .

Adding additional mixing volume before the injector minimizes or eliminates this wavy problem. Also reducing the pump stroke volume, increasing the detector wavelength, balancing the TFA in both solvents to have the same absorbance, decreasing the TFA concentration, using a column with lower hydrophobicity, degassing your mobile phase, and making sure your pump is operating properly will reduce this problem as well.