Chromatography Forum

Been tasked with quantifying dimethicone in a body creme pilot batch. The upper managment says that FDA requires the testing for level of dimethicone and if it degrades faster than the other ingredients in the body creme. Seems like FTIR is the only method (at least from an initial forray into the literature) that was found. I know that it is non-flammable so GC would not work, thus HPLC could be a possible alternative? We don't have an FTIR but do have an HPLC and GC and UV spectrophotometer. But LC prolly best suited no? Any ideas on methodology? or Instrumentation? I realize that it will be tough customer notwithstanding the considerable intellect availed on this chrom forum.

I've not done dimethicone, but I've looked at cyclomethicones (D3, 4, 5, 6) using NARP (or nearly NARP) with RI detection. IIRC, IPA is a pretty good solvent. (Sidenote: Once, just for laughs, I tried a silicone based MP -DC 200 fluid I think - and actually separated some oil soluble vitamins just to see if I could.) Stupid, perhaps, but it worked.

JUDDCC: you've lost me in your acronyms buddy---heheh--what is ILIC? what is NARP? What is RIR? What is IIIRC?

Thanks!

Oops - Sorry!

NARP - Non aqueous reversed phase
IPA: 2-propanol (isopropyl alcohol)
IIRC: If I recall correctly...
RI: Refractive index

Hope this helps!

Ahh! A mixture of two FLAs and two different kinds of TLAs!

http://www.acronymfinder.com

That old saying applies...
" When holding a hammer, everything looks like a nail ".

HPLC is not a good option for quantitation of poorly-defined, mixed molecular weight polymers like dimethicone.

Spend the time writing a purchase requisition for an FTIR. If management really, really want the data, they'll find the Capex funds. If not, use a contract lab with one.

hummm...so the scheme that JUDDCC suggested is not feasible no?

Dimethicone quantifications, only feasible for FTIR?

Agreeably there are "mixed" dimethicones but the creme formulation would contain only one form of dimethicone.

With respect due to Mr. Hamilton, I heartily agree with his sentiment in general, however I tend to disagree with his assessment of this situation in particular. Sometimes one has to do with what one has in a short timeframe - and this is frequently the case in personal care, which is a trend driven business.

First, FTIR is no panacea when assaying complex cosmetic formulations, especially when trying to do so quantitatively.

Second, in my experience, at least, contract labs will frequently only apply an established method to the sample submitted - any modifications of the method to suit the sample in question results in significant up charges and delays.

Third, with a bit of creativity and luck, I would bet that it would be entirely possible to develop a reasonably accurate method for whatever dimethicone is being used. For instance, extraction with IPA or another solvent followed by GPC or another searation mode with either RI or ELS detection might work and could actually be a reltively simple solution to the problem. It certainly might not work, and there will be issues to work out, it's not really a terribly expensive or time consuming experiment to determine feasibility.

I've done just this kind of work on these kinds of samples for many years and it is often quite possible to quantify odd, amorphous mixtures using LC. I wouldn't hesitate to take a crack at it...and I might just spend some time and try it just for giggles...

Been tasked with quantifying dimethicone in a body creme pilot batch. The upper managment says that FDA requires the testing for level of dimethicone and if it degrades faster than the other ingredients in the body creme.

This doesn't make any sense to me, this doesn't sound like a pharmaceutical product, and dimethicone doesn't sound like a pharmaceutical active to me. Is there a pharmaceutical claim? Maybe I'm wrong. If I'm not wrong, then your upper management is misinterpreting the FDA regulations.

Pharmaceutical claims include kills germs on skin, reduces perspiration, reduces dandruff, have SPF actives, etc. Skin creams which claim smoother skin or moisturizing are not pharmaceutical claims.

Our label claim is that dimethicone is efficacious; however, the root issue in-play here is to derive an appropriate analytical methodology to quantify it (%w/w) in a creme formulation. A perusal of literature disclosed FTIR as the method of accomplishing this; however, I don't have FTIR thus, JUDDC has proposed an alternative that is both reasonable and (though not promissory) worth the effort to investigate. This was my rationale for querying the chrom forum, regardless of whether the attempt fails I will have a template for the process. I think that I shall use the raw material dimeth. as a test STD and go from there prior to ordering expensive USP STD so I can work out the kinks.

It's only my opinion, and it's free, so why would it be correct?.

Almost any assay is possible if you throw time and money at it, but it's not always rational. However, for fun, lets follow my perceptions. First, and most importantly, this is not a single chemical entity, but a polymeric mixture. If you are not set up for GPC, or have an appropriate system, there may be quite a significant cost involved.

How does the National Formulary ( USP ), assay Dimethicone?
I don't have a current edition, but my older edition used IR, and no HPLC ( eg GPC with suitable detection - which is the most obvious method ) is performed on the product.

Has the NF changed?
If HPLC is used as a assay method by regulators, then developing an HPLC method becomes more rational, but if it hasn't...

How are you going to show regulators that you method works for a product when the supplier may not control, or even monitor, using that parameter?. Their batches could be different chromatographically ( even in GPC ), yet still pass NF. You may need to validate the method for each new supplier batch.

Unless the regulator is comfortable with your methodology, you may have perform further work. I suppose it depends whether you want to set up a GPC system.

If it was me, I'd tell management to purchase a more suitable hammer.

HI Bruce

Your argument is entirely rational, your points are well made, and worthy of consideration. An IR may indeed be the best way to go in the long run, but it doesn't address the question he asked. He asked how he might go about assaying for dimethicone with an LC.

If this is to become a QC release assay, then the IR method may be necessary. If it's a one off analysis, then GPC might be the easiest way for him to go and to do that he wouldn't need any specialized system beyond the appropriate column(s) (in my opinion). It's his decision. Developing an assay, looking at batch to batch variation of his raw material, then looking at a placebo should give an indication of whether he might have a hope at a reasonable method.

I'd guess that 2-5 days fooling with GPC columns and MP's, then another day looking at various batches of raw material & a placebo and he'll know whether he'll need to buy an IR or not. In my experience, mgmt would look much more kindly upon such a capital expenditure after you show them the results of a few experiments demonstrating that you cannot or should not do the assay with existing equipment.

The NF is lovely, but it's anything but definitive. For instance, the NF specifies GC/FID for analysis of a number of sunscreens, but that doesn't mean that LC isn't an entirely reasonable method to use. I'd argue that LC may actually be superior given that the NF methods are for drug substances and the matrix of a sunscreen product is significantly more complex than a single component - and there's usually lots of water around. GC's hate water, last I checked.

In a pinch, I've used an LC to assay for some things that folks here might consider crazy. Two recent examples come to mind:

Fe2+ (phenanthroline complex, then RP with PDA detection -I saw single digit ppb levels easily). I would have much rather used an AA or ICP, but don't have one and it would have taken longer to send samples out. The matrix was relatively simple, it was a one time deal, and a known addition spike gave good recovery, so it was done.

FD&C Dye lakes (metal chelated dyes). I'd be surprised if you find a single HPLC method for these in the literature, but it can be done and it works quite well. It took me a couple of weeks to get squared away.

The hammer can be used pretty creatively and I'm don't think one should limit one's creativity because it falls outside what the NF specifies. As long as the important variables are accounted for, there's no reason not to give it a shot. If it doesn't work, it could buy him an IR after all.

Just a note, not disputing your post, but just to clarify for readers.

Typically, NF was for excipients, USP was for drug substances. Dimethicone was considered an antifoam and a water-repelling agent, not an active drug.

You are indeed correct...

Perspect to this issue, we are investigating tricking out this HPLC with an ELSD unit in lieu of the UV detector. Apparantly, PDMS do not contain a chromophore; however, quantifying the amount of scattered light generated by the sample residue per a fixed droplet size of mobile phase from which the analyte is evaporated may hold promise. But I realize none of this will be as easy as the manufacturer's say it will be . Any tips or user notes?