How Much THF?

[Jimi]

So a bit of a mysterious question today. For those of you who use THF as part of your method development activities, I am curious to ask: How much do you typically use.

Now of course this is an open-ended question. And I realize that it would vary significantly depending on the sample, the column, etc. But I'm just asking for generalities.

Recently, I spoke to two people who said they often find adding fairly small amounts of THF makes a significant difference (one said 5%.....the other said 10%"......in both cases they are talking about adding these quantities of THF to a MeOH or ACN phase).

Therefore, I am now wondering how common this observation is. So I would be interested to hear whether others have also found that, when ACN and MeOH don't quite do the trick, often small amounts of THF will make the difference, and that it's rarely necessary to go to high levels of THF.

(There is a big picture reason why I'm asking, but I won't elaborate on this because it wouldn't be of much interest to chromatographers)

[Consumer Products Guy]

Yes, we've experienced that 5 to 10% THF replacing methanol or ACN can affect the selectivity of the analyte or interfering peak. so can help the analysis. We don't like to use THF, but we love it when it helps; it's a great addition to the toolbox.

[Gerhard Kratz]

I agree with Consumer Products Guy. But I would use 2-5% maximum.

[tom jupille]

The conventional wisdom is that ACN, MeOH, and THF are the three solvents whose selectivity is most different from one another and still miscible with water (hence, the "big three" for reversed-phase). most people will try to develop methods with MeOH and/or ACN and turn to THF only as a last resort because of it has stability issues, a high UV cutoff, and, quite frankly, it stinks. Aside from worries about compatibility with PEEK tubing, there really is no reason to limit THF to a few percent (aside from the fact that it stinks!). Here's an example where it was the only organic solvent:
http://www.ncbi.nlm.nih.gov/pubmed/16887315

[bunnahabhain]

Keep in mind that THF attacks PEEK capillaries. You're on the safe side with 2-5 % but I have seen PEEK burst after prolonged use with 10 %.
I have also seen the red color from color-coded PEEK being washed away by an unexperienced user (= me at that time) using 100 % THF...

[DR]

... and it's highly viscous, so just to keep pressures reasonable in your column's optimal flow range, as little as possible...

[Jimi]

Interesting stuff. So I've now heard from several people who say that one can see significant selectivity changes from fairly small amounts of THF. This is actually a very significant observation. Because, with the realization that you can often gain a lot by using only a little, many people who avoid THF may now be more inclined to add it to their arsenal.

Gerhard -- I'm curious to ask: why do you say 2 - 5% maximum? Why is it, exactly, that you draw a line at 5%? I am interested to know.

Thanks

[Jiri Urban]

Does THF addition work on "all" columns (silica)? I thought that it only works/helps on polymer-based columns (swelling).

PS: Tom, actually I kind of like smell of THF

[Gerhard Kratz]

Viscosity - backpressure and the PEEK problem. As little as possible I would run THF on a standard HPLC system. THF 100% for GPC is ok on a GPC system.

[KM-USA]

Gerhard -- I'm curious to ask: why do you say 2 - 5% maximum? Why is it, exactly, that you draw a line at 5%? I am interested to know.

We used 7 to 8% THF in a validated assay for years, no issues at all. We used THF for HPLC without added UV-absorbiing preservative.

When there was an ACN shortage a few years ago, we revalidated some methods and some used THF as the only organic, again no issues observed.