Extracting an API from a topical cream/lotion

[TimB]

Good morning Chromatography forum.

I've recently been assigned another project, and this one is actually a straight forward Reversed Phase seperation. We have to perform a stability, and that means breaking the formula and extracting the API. While i have worked on topical creams in the past, it was always on non-compendial excipients.

So does anyone have any experience with this? The HPLC seperation is actually isocratic using a mobile phase of 75% 20 mM Phosphoric Acid 25% ACN.

My first guess would be to just dilute it with the Phosphoric acid/ACN..

Thanks,
Tim

[Consumer Products Guy]

Use a solvent that dissolves the API and dissolves or disperses the matrix. In your case, if using you mobile phase as diluent doesn't work well, I'd try ACN first, then DMF and CH3OH. That's what we'd do, except we'd likely try DMF and CH3OH first, from our experience. We rarely use mobile phase as diluent, as we find no need to. When using organic-only to dissolve your sample, remember to keep your injection volume relatively low so the solvent from the injection doesn't negatively affect the chromatography.

[Dan]

Tim,

In addition to using solvents as CPG suggest, you may want to consider using heating with shaking.

Using gentle heating and shaking in a shaker-water bath, you may be able to use just your mobile phase or water:ACN, 75:25.

I would add the cream sample into an erlenmeyer flask or some other sample bottle and just pipet in (or dispense in) the solvent and then heat and shake. Then filter and inject.

As CPG noted, your solvent choice depends on your API solubility.

Regards,
Dan

[yangz00g]

Have ever heard of matrix solid-phase dispersion, check it out if not. When I was in graduate school, I had a project using MSPD tp extract capacisain from tropical cream.

You can also try to dissolve the cream in hot methonal for direct injection.

[TimB]

All very good suggestions, thank you.

I'd be interested to learn more about this matrix solid-phase dispersion. Any good papers on it?

[unmgvar]

what you can also do to help you out if your sample contains alot of oil based excipients is after dissolving your sample (generally with temp involved in the process) to put it in the fridge for several minutes and then the oily compounds will generally agregate together while your API will stay in solution.
it will work fine if your API is not in itself of oily nature

[vickig]

We have developed a number of HPLC methods for API in creams, ointments, and even toothpastes. In most cases, 100% ACN with an appropriate internal standard works the best. The idea is that you want to extract and dissolve the API but not the other crap in the matrix.
We weigh the sample directly into the volumetric, then qs w/ ACN/IS. In some cases it helps to heat the ACN (a few seconds in the microwave works well) before shaking and sonicating. If your recovery is low you may have to prepare your standard in the cream matrix as well.
Good luck!

[Consumer Products Guy]

We weigh the sample directly into the volumetric, then qs w/ ACN/IS.

Vickig: if you're using internal standard, why are you bothering using a volumetric flask - qs to volume with ACN containing IS??? Most add the exact same amount of internal standard to each sample, that is: a known repeatable amount, such as from a pipet or automated dispenser. When you qs to volume the amount of IS added actually varies depending on how much sample you have weighed out. Granted, if your sample amount is consistent, then that part may be reproducible, but I find that a little "different". At my company 98% of our test procedures, including API actives, are external standard. Many IS test procedures out there are carryovers from the manual injection days, today's autosamplers are excellent and repeatable.

[vickig]

CPS: I am happy for you that your autosamplers are so excellent and repeatable, unfortunately not every company can afford "today's autosamplers" at "today's prices". The addition of an IS, besides letting us know that our equipment is working well, also eliminates any effects of sample evaporation (not so much a problem with ACN, but can be significant with MeOH or EtOH or THF).
You have a valid point about the amount of IS varying with amount of sample weighed out, but it saves us an additional step.

[Dan]

An old method that we had used 100% MeOH to extract the analyte from toothpaste (actually, the extraction was done three times in order to "improve" the accuracy). The analyte has very low solubility in water but is soluble in MeOH. The problem with this is that the addition of MeOH to the sample of toothpaste causes a clumping of the toothpaste matrix which in turn leads to a lower extraction of the analyte.

I would expect the same problem when using 100% ACN for a toothpaste sample.

We greatly improved the accuracy (and efficiency) of the method by changing the sample preparation to first add water and stirring to thin out the sample matrix. Then the MeOH was added with some more stirring. Then filtering and getting basically 100% extraction efficiency.

The sample flask was an erlenmeyer. We pipetted in the water and MeOH. You can correct for the volume of dilution.

No internal standard needed.

Regards,
Dan

[Consumer Products Guy]

CPS: I am happy for you that your autosamplers are so excellent and repeatable, unfortunately not every company can afford "today's autosamplers" at "today's prices". The addition of an IS, besides letting us know that our equipment is working well, also eliminates any effects of sample evaporation (not so much a problem with ACN, but can be significant with MeOH or EtOH or THF).
You have a valid point about the amount of IS varying with amount of sample weighed out, but it saves us an additional step.

Autosamplers are one reason I've got three autosamplers going overnight tonight, just with stuff I prepped today. That would take me days with manual injections, and I'm on vacation Wednesday. You've got to sell to your boss that the autosamplers would increase your productivity, run during lunch, run during his/her extremely interesting meetings, etc.

[sfe-co2]

We try MeOH, ACN or even THF in my lab, sometimes with gentle warming or ultrasonication. Seems to work for us.

[sfe-co2]

We try MeOH, ACN or even THF in my lab, sometimes with gentle warming or ultrasonication. Seems to work for us.