Analysing topical pharmaceuticals

[Martina]

Dear Experts,
I am developing methods for the analysis of topical formulations such as creams and currently troches. The Progesterone troche has a polyethylene glycol (MW1500) base and I need to extract the Progesterone from the troche. I have a method from USP25 for progesterone suppositories (PEG) which I am going to use. My worry is the potential fouling of my columns with the constituents of these applications. As per the method I am using mobile phase (H2O:ROH) (45:55) where ROH = Ethanol:2-Propanol:Methanol (90:5:5) to extract the active from the troche. Is there any way I can be sure that the PEG will not foul the column(C18)?
regards
Martina

[gbalock]

Martina,
There are two approaches to the PEG problem. One is to try to keep it off the column in the first place. You could try a SPE method to isolate your analyte and then proceed with your analysis. Two would be to clean up your column after the analysis is complete. A high concentration of Methanol should wash the PEG off the column.

[Mark Tracy]

PEG is very weakly retained on reversed-phase columns. With a MW of 1500 it is sufficiently soluble in your mobile phase that there will be no serious issues. Just use a good membrane filter to keep insoluble matter out of the column. If there are oils, greases, surfactants, or emulsifiers in the formulation, that is a different story.