OptiMEM is the best media to use for transfection, but this is just used for complex formation and contain may substances like glutamax etc. which can show instability in analysis results .

Have you considered that factors in Opti-MEM media can reduce and prevent quantitative extraction of your analyte?

Thank you Karen and Bruce for the help. I want to add that from literature, I know that there are no recovery/stability problems when using DMEM + 10% FBS for this compound that I am testing.

Bruce Neagle : I do not know. Nothing from the 'ingredients' in Opti-MEM sounds alarming. That's why we have used it for the experiments, because we didn't expect difficulties. Can you give an example of something that can reduce and prevent quantitative extraction? I will look the principles up in literature and try to see if anything like that can be the case.

Karen A. Darbinyan : You are right about instable results. However, I don't understand what mechanism can cause this. Should glutamax ring an alarm bell to me? Because as far as I know it is not reactive to other compounds? And, do you mean for example precipitation/cluster-forming/adsoption to the walls? In that case, I can set up experiments for testing these hypothesis.

Depends on your analyte. But the Opti-MEM media is described as reduced. So I would expect some residual molecules are reduced. See attached;

https://www.thermofisher.com/ca/en/home/life-science/cell-culture/mammalian-cell-culture/classical-media/opti-mem.html