Analysis of polymeric components

[hajdaei]

Hello

We are trying to determine the concentration of polymeric species in a pharmaceutical. Specifically, we are looking at things like Carbopol and cyclomethicone polymers.

It seems the main challenge with these types of components is getting them into solution - especially with carbopol which is a network polymer that does not dissolve in much of anything.

Are there any ideas out there. The only thing I can think of is some kind of derivatization; but these tend to be messy, especially when there are a number of other species present that might interfere with the reaction.

Thanks very much.

[Uwe Neue]

How about using size-exclusion techniques specifically for the polymers. The small molecules would usually elute later, and as unretained peaks. SEC techniques are isocratic, so you can even use a refractometer for detection.

[HW Mueller]

Just wonder what this is doing in a pharmaceutical and how it is put there, in powder form? Is it there to modify viscosity? How, if it doesn´t dissolve?
" . . . . carbopol which is a network polymer that does not dissolve in much of anything" means it is possibly soluble enough to do one form or another of LC?
If there is really an insurmountable solubility problem, how about filtering the polymer(s) out and doing infra red analysis?

[hajdaei]

Can a network polymer even pass through a column at all (any kind of column... reversed phase...size exclusion....etc). Or will it get tangled up and not pass through.

I wasn't sure if the chromatographic approach would work at all for this type of molecule (unless it was broken down by derivitization some how)

[hajdaei]

In further researching this I've been speaking to some experts and they tell me that network polymers can never be handled chromatographically. They just get tangled up in the column and don't elute.

This does make sense to me, but seems inconsistent with some of the earlier comments on this thread.

I would like to understand better. Could you please clarify: exactly what types of polymers (in general terms) have you been able to do by SEC.

Thanks very much!

[Uwe Neue]

This is a question of the overall size of the network polymer. If the entire pill is a single network polymer, it will not go through frits and filters. But then, what is the point of determining its concentration??? In many cases that I can think of, the network polymer is chewed up into smaller pieces and is a processing component. If it is small enough, you will be able to determine molecular size, and concentration.
So I suggest that you find out more about the properties of the polymers in your sample. As a reference, styrene polymers with a molecular weight of 20 million go without trouble through a 10 micron column.