I would like to add HEPES into my cell culture medium as I have an incubator but without CO2 supply, how much should I add and how long can it last until I change the medium again?
I saw a recommendation to use 10-25 mM HEPES. The higher the concentration, the better it will resist pH changes as the cells metabolize. If you include phenol red in the medium, you will be able to see if the pH departs significantly from the desired pH. If that occurs, you should replace the medium.
i agree, 10-20mM HEPES is reasonable. Before adding though, make sure to adjust the pH of your HEPES stock solution to the level you want to work at (usually pH 7-7.2).