Chromatography Forum

Hi,
we are synthesising block copolymers and are routinely doing size exclusion on these. Normally we use water, DMF and THF, depending on solubility.
A certain class of these polymers are only soluble in water and methanol however. Water is not working properly for size exclusion at least by the methods we normally use.
Inspired by a recent article on related copolymers we consider using methanol as solvent. The article uses a 0.2 M (!) LiClO4 in methanol and polyethylene oxide standards.
Our current problem is that we are not able to dissolve very much in this eluent and we have been wondering if this high concentration is a typo.

Anyway, does anyone have experience in doing SEC with methanolic eluents? There does not seem to be much literature as far as I have been able to find.

Thank you in advance!

Regards,

Jeppe

Though my experience is with biological macromolecules, it seems clear that water or MeOH should be no problem if the stationary phase is compatible (i.e. is wettable by water, probably all column manufacturers offer such columns). Of course, the shape of the polymer will depend on solvents, so the "size" you see (order of elution, peak shape) might be different when solvents are changed.

Thanks for your reply. Actually we do have compatible columns, somebody bought them...my question was more along the lines of what to use for standards and any experience on ionic additions to the solvents.
PEG's have a tendency to stick to columns in methanolic solutions, giving rather broad eluting peaks eluting late(if at all). The addition of salts might overcome this problem, my problem is just that I never saw anyone do this, except for the one reference...where the ionic strength is so hight that very little will actually dissolve.
Otherwise I agree with your considerations.

But basically we would of course like to get as little adsorption and as high a degree of real size exclusion as possible - but that is probably always the case

I guess I will have to try it out, thanks anyway.

Regards

Right, you wouldn´t want to put salts which increase a salting out effect, but then I don´t know how these chaotrope-lyotrope scales work in MeOH, thus I don´t dare to make a suggestion, except that there might be some parallels to protein SEC (adding something that lowers surface tension of MeOH, etc). Actually, if I had to do this I would look for a solvent to add to MeOH which increases the solubility of PEG´s.
I also wonder what the addition of urea would do.