I want to measure some secretary proteins in the supernatant and I want use conditioned media. I have proceeded in this manner: seeded the same number of cells in the same volume of medium, treated the cells with different reagents (or vehicles) for the same period of time and taken the same volume of conditioned medium to test. I would say it is normalized. Note: IN DMEM I did not add FBS or any antibiotic. Is this method correct?