Chromatography Forum

Hi everyone

I have an HPLC method to determine three actives. The impurities of the API have a max impurity limit of 0.1%. At this concentration of the actives (eg. 0.1mg/ml) the impurities are not detected. If I increase the concetration of the impurities to ±10% with respect to the API the impurities are detected and they co-elute with the API. Under normal conditions we would only be concerned with the impurities at the max impurity limit (in this case 0.1%). Is my method still stability indicating although the impurities are co-eluting with the API at the 10% level?

Many Thanks
Mike

Only in case the impurities are also degradation products.At 0.1% level they will not affect.

If your known impurities co-elute with an API, your method is not stability indicating because it lacks selectivity.

Stability indicating assay means that no peaks interfe with the peak of analyte. The impurities are synthetic by-products and degradants. The first group isn't changed during the stability study and , in case you are to control their content ( for exanple 0.10% each) than you can adjust the concentration of the main peak in the range the those impurities are non detected even when co-eluted with the main peak. For the degradants , which supposed to growth during stability study, this doesn't work.

Bottom line: keep the synthetic impurities under the LOD level for the prescribed concentration of the main component and separate degradants. It will be stability indicating assay.

Of course, it's always better to separate everything, but in some cases you can follow the described above.

Thanks for your comments/suggestions.

MC

If your proposed specification for that related substance (degradant) is say 0.5%, then I would agree that if that related substance does not co-elute at say 1% (since you plan to validate a wider range than 0.5%) then it is okay to say your method is stability indication provided you show that it does not co-elute in the robustness study (hope you do the robustness study with related substances at the specification level). If the related substance does co-elute with the active in the robustness study you may have to tighten your mobile phase/sample preparation and/or have a resolution solution in the method, then you can claim that it is stability indicating method.

I found stability indicating assay in stress condition using hydrolysis with basic, acid, peroxide, light, and heat. Can we change the media (water) to a mixture of organic solvent-water or pure organic solvent for the method, especially for water insoluble- or slight soluble API?
Please give me information about any references or articles to this case.
Thanks,
SYX

We do it routinely in our daily practice. The choice of organic solvent is very important - should be extremly stable under stress conditions,with the boiling point close to those of water, pure enough not to interfere with the peaks from the sample (I prefer pure Dioxane). I guess I can find the references for you, if it's necessary.