Chromatography Forum

Can anyone tell me how a vendor can analyze and send a certificate of analysis of a compound based upon area% calculation on a UV-VIS DAD HPLC? This just blows my mind as not all compounds have chromophores. Impurities have the potential to not show up at all - or have wildly different response factors using HPLC.
What am I missing that I get some COAs based upon HPLC?

You are right, but the vendor generally doesn't have to produce COAs that fit for your purposes, unless the vendor is a manufacturer of certified reference materials developed to be suitable for your analytical methods.

You are entirely correct some things will just never show up by uv-vis so often other detectors are used such as fluorescence, charged aerosol or IR and mass spectrometry (much more than just a detector but as an example)
But if your CofA for example just said 99% by HPLC-UV then that is coming with essentially the caveats you stated, this product is 99% pure and 1% impurities *that have a chromophore *that absorb at the wavelengths we have set our detectors to or scanned across * that are present at levels above the sensitivity of our limit of detection.

You can compensate for these limitations in your impurity profiling by doing things like comparisons of peak sizes and %weight, if I have 1mg/mL of standard I know to be pure and get a response from the detector of 100units and I prepare a sample at 1 mg/mL and get a response of 95units then that sample is less pure than the standard whether I can see it on the chromatogram or not.

You can obviously do many other analytical methods and build a profile of impurities with no chromophores but every CofA is limited to the detection capabilities of the different analysis methods.

A good CoA generally offers a few different purity factors based on orthogonal testing methods (LC or GC, titration, moisture...) so that one can have a more complete characterization of the material in mind when using it. Of course the additional testing brings with it additional cost for the material.