Chromatography Forum

Dear all,
Maybe my question looks a bit stupid; however I would be thankful to have your point.
Ethanol is not used (not preferred?) as solvent for HPLC; while the lower alcohol and the higher ones are often used. Is there any reason behind?
Thanking u in advance

Probably because you can drink it and pricing is relatively cheep compare to Absolute.

Probably because you can drink it and pricing is relatively cheep compare to Absolute.

I don't know about that. Personally, I find that THF has sort of a piquant aftertaste (but gives a helluva hangover ).

Just joking! Seriously, from the point of view of selectivity, all the alcohols are expected to be roughly similar, so from that point of view, they are more or less interchangeable. Methanol has the lowest viscosity of the three (therefore provides a higher plate count and a lower back pressure), which makes it the usual first choice. Isopropanol is used occasionally in normal-phase chromatography (it is miscible with hexane in all proportions) and in protein separations (for solubility reasons).

There is a hesitancy due to the licensing issue involved. This depends on your locality, and really won't be a serious cost or management headache in many instances. There is a potential for abuse, but there are many other laboratory chemicals with the same issue, toluene, nitrous oxide, etc. Reasonable inventory control measures can address the abuse issue.

My understanding is that ethanol should make an excellent HPLC solvent. I believe it has a significantly lower viscosity over 2-propanol and 1-propanol, but still gives similar polarity/London adjustments over methanol.

I have seen a few references regarding this, but not many.

Anyone with some experience out there?

We very occasionally use ethanol as HPLC solvent, only when a procedure taken from literature used it, and we didn't run enough or care enough to investigate. Our HPLC ethanol does contain 5% methanol and 5% IPA as denaturants, just be consistent with your ethanol supply. This brings to mind an experience with a contract lab about 10 years ago which was doing a GC ethanol assay; they used HPLC grade ethanol as standard, and it was only 90% ethanol due to the denaturants (they just assumed HPLC grade was absolutely the purest). For that GC assay we use here 200 proof 40-B ethanol as standard, about 99.7% ethanol.

The only problem using EtOH (99.9%, gradient grade) in a normal phase (silica) analysis of proline derivatives is that it takes up air relatively fast after degassing via vacuum.
(We are using EtOH because evetntualy the effluent will be infused into living beings, Tom please don´t have a fit, its done all the time!)

Ricardinio,

Here are some references about the use of ethanol. I think Collins works in Brazil, where I seem to remember cars are run on ethanol. I think it is produced on a large scale from bio-fermentation. If there is so much of the stuff around, and there are no regulations which makes it difficult to use in the laboratory due to the possibility of the staff drinking it, then why not use it? Otherwise, I see no compelling reason to switch from methanol, which has very similar chromatographic properties but is less viscous than ethanol.

Ribeiro RLV, Bottoli CBG, Collins KE, et al.
Reevaluation of ethanol as organic modifier for use in HPLC-RP mobile phases
JOURNAL OF THE BRAZILIAN CHEMICAL SOCIETY 15 (2): 300-306 MAR-APR 2004
Times Cited: 0

2. Ribeiro RLV, Grespan CB, Collins CH, et al.
Optimization through factorial planning of the use of ethanol : water as a mobile phase for reversed phase HPLC
HRC-JOURNAL OF HIGH RESOLUTION CHROMATOGRAPHY 22 (1): 52-54 JAN 1999
Times Cited: 5

One other problem with 100% ethanol is that it is famously hygroscopic. That is a real nuisance for normal phase.

Mark,

Thanks for bringing up the hygroscopic nature of ethanol. I thought about that after my orginal post here.

Are there any common HPLC solvents that are significantly hygroscopic?

What about pure 2-propanol?

If ethanol is cheaper but has similar properties with methanol; why not favor it?

Ethanol has higher viscosity = higher back pressure and lower plate count.

Ricardinio, where do you get EtOH that is cheaper than MeOH? Here MeOH is cheaper by up to a factor of 2.

In the United States, 100% ethanol is heavily taxed because it is drinkable. Strangely enough, ethanol manufacture for fuel is subsidized.

Many states, Pennsylvania for one, will allow laboratories to purchase a wholesale liquor license for the purpose of using ethanol in the laboratory. With such a license, the cost of ethanol can be quite cheap, provided the volume of usage is enough to justify the cost of the license.

If you are doing reversed phase or normal phase ethanol will contain a certain amount of water which makes its performance variable.

Since ethanol will attract water from the air, it will increase its water content with time even when tightly sealed.

While with reversed phase chromatography this water content can be compensated for, it will sometimes damage a normal phase column by absorbing water irreversibly, or at least requiring its removal and a lot of work, time, and testing to verify the column works as it did before its contact with water. (in orther words: IT COSTS A LOT OF MONEY)

Since it is often denatured, ethanol is difficult to purify, expensive because of taxes if bought in pure form, and can be stolen and used for entertainment purposes if not guarded carefully.

Methanol, isopropanol, and butanol can easily substitute for ethanol for most applications at a greatly reduced cost.

So why use ethanol?