Chromatography Forum

Hi everyone !
A technical question about a situation I was hoping you could help understand. I am not a HPLC specialist, so it could be quite easy, I don't know.
I use to work with analytical standards from Sigma Aldrich for HPLC concentration measures. This works fine for me, but looking at the analysis certificate provided with the standard, I couldn't understand where they got the precise concentration value for this sample.
I don't know if they use the same technique for all their standards, but with mine they use the peak area % value from a HPLC test with a UV detector to establish the concentration of the substance. This seems a bit approximatical to me, as depending on the wavelenght, the peaks of some impurities could be underestimated, or even invisible because of the solvent choice.
Could anyone confirm that this method is sufficiently precise (to justify the price of such tiny samples...) ? And why it is ?
Thanks a lot guys !

I would say that most of the time the method suffices. Think about this: to obtain the final pure compounds, many steps are needed to purify some raw material. The first steps will remove impurities which are very different from the desidered product. At each step, the purity of the product increases, and impurities which are very similar to the product become predominant over other unrelated impurities. Ideally the final step(s) will remove these last "product-similar" impurities and leave only the compound of interest.

Therefore if any trace of contaminant is left, it will be something similar to the compound, with a similar structure and similar structural groups. Therefore, if you can see the compound in HPLC, it is very likely that you will be able to see also the impurities, and these impurities, if present, will have an absorption coefficient similar to the analyte. The same could be said for using other detection methods, such as fluorescence or electrochemical detection.

I agree that sometimes, however, this check is not enough, especially for ultrasensitive MS work...