I'm performing a robustness study for a method validation, and I have 6 conditions to test, with each condition requiring a 12 hour LC run. I have been preparing fresh standards/samples each day (samples are from the same batch)and was told this is incorrect!?! The standards/samples are stable for 3-5 days at 2-8C, (will degrad about 0.5% over 5 days). So what is the best way to perform robustness?? Since the LC system is started each day with a different mobile phase-does it matter if I use fresh standards/samples?

As robustness is the main aspect of your testing then surely having samples prepared from different batches is OK if not ideal. Samples are better prepared each day though so as not to introduce the issue of sample stability.
Just a comment!!!

If you consider stability to be an aspect outside of the robustness evaluation then surely the same solution injected throughout the study would be more appropriate. I would infact degrade the solution to enhance the study and consider the robustness of your method to determine those products.Are you using some sort of stats evaluation software?

I want to perform a robustness study for a HPLC method validation of an active ingredient assay. I wonder if someone can help me to construct an experimental design. A protocol or example would be the best help. Thank you very much.
Ha Minh Hien