High-Glucose DMEM with Phenol Red, Glutamine and HEPES

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• HEPES buffer in cell cultureHEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) is a zwitterionic organic buffer used in cell culture to hold medium at physiological pH without depending on incubator CO2. Its pKa is about 7.5 at 20-25 degrees C and about 7.3 at 37 degrees C, giving useful buffering across roughly pH 6.8-8.2, and it is normally added to medium at 10-25 mM from a sterile 1 M stock. Because HEPES buffering does not rely on the carbonic acid/bicarbonate equilibrium, HEPES-supplemented medium resists the fast alkaline drift that occurs when a flask leaves a 5% CO2 incubator.
• EMEM vs DMEM: What the Modification Actually ChangedEMEM (Eagle's Minimum Essential Medium, also sold as MEM) and DMEM (Dulbecco's Modified Eagle Medium) are the same medium one generation apart: DMEM is Eagle's formulation enriched, with roughly four times the vitamins, about twice most amino acids, twice the glutamine, added glycine and serine, ferric nitrate, and 3.7 g/L sodium bicarbonate against EMEM's 1.5-2.2 g/L. The practical consequence is that DMEM supports fast-growing, metabolically demanding lines such as HEK293 and NIH/3T3, while EMEM suits slower, less demanding adherent cells and primary lines - and because DMEM's higher bicarbonate is formulated for 10% CO2 while EMEM's suits 5%, the two are not interchangeable without checking your incubator.