Advice on paraben method

[chemgeek]

I trying to work out a method for the detection and quantitation of Methyl and Propyl parabens, the seperation and detection of these 2 components are the easy part, which we have easily figured out.

The issue we are having is the samples contain a relatively high level of Benzoyl Peroxide (aka BPO) (~200X that of the parabens). We have observed the BPO has killed all of the columns used within 10-20 injections (Compared to our BPO method in which the columns last longer with a lower concentration; ~500-1000 injections). We are looking at trying to selectively degrade the BPO, but are encountering some issues with the degradate products of the BPO co-eluting with the parabens as well as the chosen internal standard (Acetophenone). Sample formulations contain varying levels of components typically found in topical OTC treatments (I know, big help with this tidbit)

Currently I am looking at doing the standard screening process things:

• Doing some degradation experiments to determine the optimal conditions for degrading the BPO while maintaining the parabens.
  At the same time I'm going to look at alternate Internal standard choices for specificity
  Determine if we will have to wait to add the internal standard to matrix post heating.

Has anyone encountered this that can provide some illuminating guidance? (My first choice would be to do away with the internal standards and just go with an external standard, but our QC department doesn't like that...) Also I am limited to HPLC, with a DAD - no new and nifty detectors available <sigh>.

Thanks!
Dave

[Consumer Products Guy]

Do away with the internal standard - with today's modern autosamplers, internal standard quantitation is not used so much in the pharmaceutical industry for stuff like this. OK, for parabens, I assume you have some acid like phosphoric acid or acetic acid in your mobile phase, and are using UV at 280nm or so. I'd use a modern Type-B deactivated RP-18 column, use either methanol or water as the aqueous portion of my HPLC eluent. I would also degrade the BPO first since it's causing you short column life. Tell your QA department to join the 1980s and direct them towards external standard with autosampler for stuff like this.

[chemgeek]

Tell your QA department to join the 1980s and direct them towards external standard with autosampler for stuff like this.

Beleive me I'd very much like to do that, but since I'm the FNG guy and a contractor for the 1st six months I don't think it would be very wise for my career. Coming from the big pharma world I completely agree on using external standards, but we are still doing duplicate injections here and most methods are using 5 micron, or larger, columns. Only just now beginning to look at 3.5 micron columns, and 1.7's are not even an option now. I miss my optimized HT 1100's...

You are correct on the chromatography points, I guess I was not very clear, what I'm hoping is that someone can give me some guidance on getting the BPO out of my samples, either through temp degradation or otherwise.

[shaun78]

The company I work for currently makes a perscription BPO cream, at a higher concentration than what I would presume the OTC brands are ... hence the reason why it is a perscription.

Anyway, the point being, we have never had problems with the columns we have used for this method, and some columns are quite a few years old. Are you sure the BPO is really the root cause?

[chemgeek]

The company I work for currently makes a perscription BPO cream, at a higher concentration than what I would presume the OTC brands are ... hence the reason why it is a perscription.

Anyway, the point being, we have never had problems with the columns we have used for this method, and some columns are quite a few years old. Are you sure the BPO is really the root cause?

Are you able to share any of this information, (Column, diluent, mobile phase?) or is it considered proprietary? I am working from what I have been told by the current chemists running the method, and their experiences. Unfortunately I do not have much personal experience to rely on for this analysis.

Thanks, even if you can't share the method, your response give me a lot of hope that there is something out there that should work... FYI we are at 1 to 10% BPO (w/w) I beleive...

[shaun78]

I would not consider the method I am currently using to be proprietary at all.

If you have a somewhat recent edition of a USP, lookup BPO in that. You can run the method as is except in place of the L1 column, use a Synergi Max column (4.6 x 150 mm, 4 micron).

The methylparaben will closely elute with one of the degradation compounds (benzoic acid if I remember correctly), but you should always have a resolution greater than 2.0 if you use the Synergi Max column.

Also, this column substitution I made for our method is not "legal" by USP standards. A Synergi Max is not a L1 designated column.

[chemgeek]

Thanks Shaun, that work has been put on hold for now but I will go back and look at the Synergy Max, I have used them in the past with good results so I am hopeful things will work.