Leibovitz L-15 Medium w/L-Glutamine, HEPES, TrisDescription Product Name: Leibovitz L 15 Medium w L Glutamine, HEPES, Tris, Low Sodium, Phosphate Free Catalog No: PG060 Product Format: Liquid Storage: 4C General Information: The most commonly used buffering system for mammalian cell cultures is a bicarbonate CO2 system, which requires CO2 regulators and incubators to supply a constant level of CO2. As a replacement, Leibovitz developed a bicarbonate free medium, L15, with relatively high levels of