Chromatography Forum

Hi, Im having trouble with the analysis of benzoyl peroxide gel containing an antibiotic (which is run on a separate method).

The solvent is acetonitrile water.

The method is run at low pH and is gradient.
Wavelength is 254 nm
The benzoyl peroxide degrades to form benzoic acid quite quickly, and im wondering if there is an issue with sample stability.

Anyone faced similar problems, or have any ideas what could be wrong

Also does anyone know what the USP limit for benzoic acid in benzoyl peroxide gel is?

Thanks

Tina

We looked at this about 5 years ago, and here's what I wrote down then. I just looked online for you, and USP doesn't appear to list any limit in BP gel for benzoic acid content. It also looks like the monograph hasn't changed since then.

2005, reference to USP 26 comments:
USP details conditions to verify system suitability of the chromatographic system but a column of different dimensions and detector wavelength is detailed for the actual assay. USP details the archaic 254nm wavelength and uncommon column dimensions. USP has apparently not modernized this to take advantage of readily-available variable wavength detectors or modern more efficient HPLC packings. The USP also details use of internal standard, common practice when manual injection was used (before the precise and accurate autosamplers in use today). We used 280nm and a modern Type B RP-18 column, and got very nice peaks. Mobile phase was ACN, water, a little acetic acid. We used external standard for quantitation, got one peak in BP standard, one peak in sample with BP, and no peaks in placebo sample (so we didn't observe any benzoic acid peak). Samples were shaken with ACN, then filtered. BP raw material has certain amount of water in it, so I don't think your sample would be breaking down after injection.