Hi,
I'm using a mobile phase 50/50 tetrahydrofuran/acetonitrile. I have had some peroxide problems due to dated THF. Anybody having some experience, would it be better to prepare large amount of the mobile phase at once. Or just mix the amount needed each time.

In another words wich way THF forms more peroxides; stored neat or stored with acetonitrile?

I gues this would be just a matter of testing but it would save me some time if somebody has tested this before.

Thanks

I would ask a futher question:

There is THF (stab with BHT) and 100% pure THF.

Does this have an influence for the HPLC or not?
Does this block peroxides in THF/ACN ?

I am not sure of the UV spectrum of BHT but I would expect it to absorb strongly in the "commonly used" regions. This will increase the background signal level which may cause baseline problems (noise). This is, of course, assuming you are using UV detection. I can't say for certain whether BHT would have any effect on the separation. For some applications it might, for others it might not. My preference is to prepare the amount of THF needed for a day and not use or refilter "old" THF or THF-containing mobile phases. You could extend the life of the THF by buying it in smaller bottles or by purging an opened bottle with a dry inert gas before closing it. You could also get a solvent reservoir that allows you to maintain an inert gas atmosphere in the reservoir. Be careful with this if you are using a prepared mobile phase (for example 50-50 AN/THF) as the inert gas purge could change the composition of the mobile phase. Obviously, the faster the gas purge, the greater risk of this happening and causing a problem.

This is purely theoretical: It could be expected that oxygen dissolves to a lesser extent in THF/ACN than in THF. Also, autoxidation is often accompanied by autocatalysis, ACN does not appear to autoxidize easily. These factors would tend to lead to the conclusion that THF/ACN has a somewhat longer shelf life.
Partially theoretical: BHT and peroxides can accumulate (depending on conditions) at the head of the column giving possibly delayed baseline drift and problems due to equilibrium shocks like injections (ghost peak...).
Practically: Russīs suggestion (made also above?) is something I will take up in the future as well, 2.5 L bottles could never be used to the "last drop".

I don't use THF much these days but has anyone tried using a small alumina column before the injector to remove the peroxides.

Thanks for all! Wery usefull discussion.

I use UV at 200 and HPLC grade THF without stabilizers (don't like the idea of loading BHT into the column). I've seen a reproducible ghost peak in the blank near to my analyte retention. This has been due to aged THF in the mobile phase (I'we done a peroxide test from the MP with acetic acid and potassium iodide and it was clearly positive). I also took the THF out from the gradient (I don't need it when I'm running blanks since it is only a column wash after each run to speed up long retained peaks in the sample matrix). The ghost peak got smaller after each run by this way. I have tried different HPLC THF suppliers and have found one satisfying grade with a peroxide spec. max 0.010% at the time of batch release. I'm still not completely happy yet because this one also goes off quite quickly (max 1 week) and there seems to be some bottle to bottle variations as well (greatly depending the closure of the bottle and storage conditions??).

Few questions:

1. How do you purge with nitrogen before closing the bottle? Is it just conducting some nitrogen into the bottle mouth (or bubble to the solvent) and close quicly and seal using arafilm?

2. Would it be better to store the THF in the fridge? Until now it has been in room temp.

3. Anybody know a good test strips to test THF for peroxides (product info)? I found one peroxide test (Mercoquant) but I have been told that this is only for water analysis.

Tom's idea sounds interesting. I'm not sure weather I could use it though, being a validated method..

Thank you for all!

We use Fisher THF in 1 liter bottles, so opened bottles don't last long. Also our THF reservoirs are brown glass.