Chromatography Forum

greetings,

Dear cinematographers, I was asked three questions during my interview. They are:

If you can not get 100% assay, what could be the possible reasons. I can think of is: sample preparation of the finished product, weighing of your sample/std, what else could it be?

the assay is 97%, there is 1% impurities, 0.2% waters, 0.3% OVI. Where did the other 1.5% go? one of the reason is some impurities do not have UV absorbency at this wavelength. what else could it be?

when they did validation for a dissolution method, their std only get recovery of 97%, which is low, what could be the reason?

thanks a lot in advance

On that failure to get 100%, that partition coefficient that we love so well (because it gives us separations in chromatography) can turn around and give us a swift kick in the sample preparation. If you extract a spike from a matrix, you can lose some in partitioning - which can be improved with more exhaustive extraction. Or you may have irreversible adsorption to matrix or labware. (And if you do that exhaustive extraction, you may have to evaporate excess solvent and you are likely to see some analyte go away with the solvent as well.)

And if you are doing method development, you have to watch for decomposition of analytes. (I think of a GC method for an ethyl ester, with the standard made up in methanol - and there were two peaks that changed in ratio as the standards aged...)

On that 97% assay: the 1.5% is indeed for something you could not see. And it may have been the haze that was removed when the sample was filtered - if it was filtered. Or it was from losses in sample prep.

And losses of a standard - see reasons for losses above.

And, I'm a GC guy. But, sample prep is usually the killer for me.

The most straightforward (and important) reason for an assay of less than 100% is that there is indeed less than 100% in the sample !!

Peter