Merck, SRE0065-1L, HEPES solution, 1M

Application
HEPES buffer preserves a normal physiological pH environment and is commonly used as a buffer in cell culture applications. HEPES buffer provides no nutritional benefit to cells, but adds extra buffering capacity to the cell culture particularly during experiments performed outside the carbon dioxide incubator.
This 1 M stock solution contains HEPES adjusted to pH 7.35 with sodium hydroxide. Add the concentrated buffer to the cell culture medium to reach the desired concentration (typically 10–25 mM).

Notes: If precipitation is present in the concentrated buffer, gently warm the bottle to 37 °C and mix until completely dissolved prior to dilution.