XTerra coumn with low pH, TFA, high flow, high temperature

[marina1111]

Hello everyone!
I wanted to ask if it is reasonable to use XTerra column with TFA containing mobile phase (more than 0.1%, pH=1.3) at temperature of 40ºC and flow 1.7. Will the column be ruined in days? If, by chance it can be done, can I raise the temperature even more?
Thank you.
Marina

[Kostas Petritis]

The XTerra MS and Phenyl are stable from pH 1-12 while the XTerra RP is stable from pH 2-12 so if you use the XTerra RP it won't be wise to use it at the conditions you mention.

0.1% TFA has a approximate pH of 2.3 so you really operate at higher TFA concentrations. I would say that a priori you are OK with the conditions that you mention for the MS and Phenyl columns. I would expect though the column lifetime to go down lineary or even expondentially if you go even higher in temperatures...

[danko]

Hi Marina,

You don’t mention the particle size of your stationary phase support, so I assume it is 5 μm.
If so, I would recommend you to set the flow rate down to 0.9 – 1.1 mL/min instead of raising the temperature. Thus you will most probably achieve higher efficiency, longer column life (due to the lower temp.) and last but not least you’ll safe a lot of mobile phase. All this is valid if the retention time is adjusted to the same as your current retention time.

Good luck

[marina1111]

Thank you for the answers. I overlooked the differences between the Xterras. Hope there was not too much demage. I think Gemini column is stable at this pHs. I do work with the low pH – (Ammonium Acetate+Ammonium hydroxide+TFA to the pH). I work with this strange phase till I find something better, becouse I have peak broadening and even splitting at high concentrations (puity test) with normal ion pairing (sulphonates). I will be glad to here additional adwises.

[Uwe Neue]

All information that I have shows that the matrix of XTerra is more stable than that of Gemini. The difference that counts at acidic pH is the bonding type. A trifunctional bonding is more stable than a monofunctional bonding. XTerra MS is based on a trifunctional bonding, XTerra RP is a monofunctional bonding, and therefore has limitations at acidic pH. A trifunctional bonding or similar approaches are recommended for acidic pH.

Peak splitting is not caused by a dissolution of the surface, so you can count this out as the cause of your problem. However, if you are looking for the most stable phase at ACIDIC pH, I recommend Atlantis T3.

[HW Mueller]

Acetate, TFA, sulphonates..., an interesting concoction. It should be best to stop this immediatly to have more time to find a working method.

Danko,
how does one save a lot of mobile phase by lowering flow rate? Are you assuming long periods of idle (no analysis) flow?

[danko]

how does one save a lot of mobile phase by lowering flow rate? Are you assuming long periods of idle (no analysis) flow?

Hi Hans,

As I mentioned, the retention time should be adjusted to the normal/current. Let’s assume that the current retention time for the main peak is 10 min. And the whole run 20 min. So 1.7 mL/min multiplied by 20 min equals 34 mL per run. Now if one sets the flow rate down to 1 mL/min the result is of course 20 mL per run.
Naturally, there will be needed a little bit more organic modifier in order to achieve the same retention time, but the net result will be mobile phase savings especially on the waste front The latter is almost as important as the usage of chemicals under preparing the mobile phase – in my world anyway.

Best Regards

[marina1111]

Thank you for the answers. I do not use the TFA and sulfonates together. With sulfonates I have peak splitting – only at high loading. The other method – with Ammonium and TFA - I found for some compound. They do promise pH range 1-12 for Gemini. I have more than one main peak and a difficult matrix. May be a half polar mobile phase should be used.
Marina.

[HW Mueller]

Marina, it is difficult to see what you are doing without telling what compounds and matrix you have.

Danko, ok, more organic......