Method validation for active substance - interference

[H.Thomas]

Dear Listmembers,

we have to validate analytical methods for the determination of pesticide active substances in preparations according to SANCO/3030
http://ec.europa.eu/food/plant/protecti ... c13_en.pdf.

The specificity of the method has to be shown by evaluating the degree of interference from impurities; they should not contribute more than 3% to the total peak area of the target analyte.

You could say, just use a blank, but usually you dont have one and OTOH you do not catch the intereference from impurities in the technical product even if you had one. So the only solution is to do standard additions of the pure active substance to the preparation.

Does anybody have an idea, how one could calculate the % interference from the measurement of the preparation and standard additions?

Best regards,

Hartmut

[Bruce Hamilton]

Because I keep getting an access error, I'll keep this brief.

You need to show you have resolved the impurities from the main peak, and the best method is to analyse on columns of differing chemistry and improved resolution, preferably with a suitable detector ( mass spectrometry or, less preferred, DAD ).

If you achieve resolution, you don't need to perform standard additions.
I can't see how you can use standard additions of the main compound, even by adding an internal standard to improve precision, as you don't have the spectrum of the putative impurities - which could be very different or even identical to your compound. If the extinction
coefficient is identical, then UV detection would be unsuitable.

Only if the impurities have a significantly-different spectrum and molar absorbance will you pick them up if they co-elute with your compound..

Please keep having fun,

Bruce Hamilton