Gel Sample Preparation Issue

[VJ]

I am developing a HPLC reverse phase method for the Finished product which is in GEL form using c18 column. GEL contains active drug, Carbopol 940(gelling agent, carbopol is water solubel), proplylene glycol and some other excipients.
Finished product which is in GEL form is water soluble. After adding some acetonitrile or methanol it gets cloudy. so it is insoluble in methanol and acetonitrile but soluble in water. when i inject active by it self i get a separation but problem here is the active drug in gel. My active drug is water and methanol souble.
What should i do ? have anyone worked with gel formulation?
should i filter through syringe? what type of filter?

[TimB]

If the entire gel is water soluble couldn't you just dissolve the gel in water and analyze it from there? You may get peaks from other things, but that shouldn't be a problem to deal with. If you can't use water what about buffers or THF?

[Consumer Products Guy]

I think I'd extract the gel with methanol containing some sodium hydroxide, so the polyacrylic acid gel agent will precipitate, then filter through a 0.45u membrane to clarify. I'd try to keep the gel agent from being injected, we've seen that accumulate on the columns and build up head pressure pretty quick.

[VJ]

Consumer Products Guy, i like the idea of precipitating the gelling agent. colud you explain the the reason of using NaOH with Methanol ? how strong NaOH has to be, for exampleL 1 N or 0.1 N ? Please let me know.

[Consumer Products Guy]

Na polyacrylate is insoluble (or mostly insoluble) in methanol, so it's held back by the membrane filter. We were assaying a hand sanitizer gel by HPLC and had a similar issue, all went fine until maybe 20 injections, and we could see that the backpressure was slowly increasing with each injection. Rather than limit ourselves to just a few injections per sequence, I decided to separate away the polyacrylate away before injection. I think I used about 0.5N NaOH in methanol, can't check, not at work now. Our mobile phase was slightly acidic so injecting a tiny bit of basic methanol did no damage.

#1. "Crap that never makes it to the column never needs to be cleaned out"

#2. Sometimes cost efficiencies dictate that #1 is over-ridden, due to labor costs being higher than equipment or supplies cost

[Uwe Neue]

Actually, your comment #2 is absolutely correct. When I first thought about the problem, I was inclined to say: just inject the stuff and see what is happening. I refrained from making this recommendation, when my second thought was that VJ may not have as easy an access to columns as I have.