Chromatography Forum

Is there any restriction on methanol content in mobile phase, when bare silica column used?

Is there a problem of "silica dissolution" and as result, shortened column-life?

Thanks in advance.

I am not sure what you mean by your question. Are you doing HILIC or normal phase chromatography?

Silica is more likely to dissolve in water than in methanol. I believe that even in water this process is very slow until a pH of 6-7 is reached and is clearly much more serious at high pH-alkaline solutions can etch glass.

If you are doing HILIC, you need to keep at least a few % water in the mobile phase for the mechanism to work. Alternatively, if you have a large proportion of water you may not be able to retain your compounds.

As you know methanol dissolve bare silica but, according to my opinion and experience (not much for real), it'is usually ok if you use less than 10% in methanol.
bye

Vincenzo

Vincenzo, 10% methanol ... and the rest?

Could this "methanol dissolves silica" come from statements which probably correctly mention that methanol is more likely to attack a reverse phase (ODS, etc.) column than ACN?

CH2Cl2 or ethyl acetate?

I am not sure what you mean by your question. Are you doing HILIC or normal phase chromatography?

Normal phase, with miscible solvents, of course.

I guess if you are doing normal phase, than you have a relatively small percentage of methanol in your mobile phase. You have nothing to worry about at all.

Just look at your bottle of methanol. Is it glass (silica)? Does the glass dissolve in methanol? This is an extreme example because the surface area of a glass bottle is much smaller than that of porous silica, but it will do as a guide.

Do make sure to use "dry" MeOH as a little water can foul up NP runs.

I've used anhydrous methanol 100% to wash silica columns in the past.

No problem.

I never heard of MeOH dissolving silica but... it is not an usual NP eluent anyway - at least in large proportions!

I agree with all that say it shouldn't be a problem!

I have used NP mobile phases saturated with water for some unusual slectivity and never had any problems . silica columns can be dehydrated by washing with anhydrous IPA/hexane.

JM

Methanol is not a problem, nor is any other alcohol. Don't forget that silica is sand ... you need to boil it in hot water, before it changes slowly.

However, at elevated temperature and under conditions where you remove water, alcohols can form esters on the silica surface and change the properties of the packing. It is an equilibrium, and water will reverse the reaction.

In any practical situation, methanol can be used without a problem.