Chromatography Forum

Please help me with two of my questions about HPLC assay:

1. I read a document saying" report HPLC assay results on the dry-basis as well as it's as-is value". What's the difference between the dry-basis value and as-is value?

2. "Weight/Weight assay result vs. %AUC results. My understandng is weight/weight result is obtained by using external standard method; %AUC result is obtained by assuming response factors are the same for every peak and calulation of %peak area. Am I correct about this?

Thanks for your help!

In the first case, the "as is" method weighs the sample without any treatment and runs the HPLC. The "dry basis" method does a % water (and/or % solvent) measurement on a separate aliquot, and adjusts the "as is" assay results for the volatiles. Either that or they dry some of the sample to constant weight before taking an aliquot for HPLC assay.

Just an additional note. If you are reporting on a dry basis, ensure that you dry the sample and standards as described in their methods/monographs, and use the data for both calculations.

Please don't just dry the sample, and use an "as is" standard without correcting for water/volatiles in the standard. That technique often explains results over 100%.

You are correct in understanding % weight/weight and % AUC.

Please keep having fun,

Bruce Hamilton

Thank you very much Mark and Bruce. That helps a lot.

I wil try to keep having fun