HEPES

HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid ) is an organic chemical buffering agent that is widely used in cell culture to maintain physiological pH.

HEPES is recommended for the protection of frozen solutions of enzymes from freezing-induced pH changes.

Lepe-Zuniga et al. reported a phototoxicity of HEPES when exposed to ambient light by the production of hydrogen peroxide. For best repeatability of results it is then strongly advised to keep any HEPES containing solution in darkness as much as possible.

Fears that HEPES may serve as a nutrient source for aerobic bacteria have been shown to be unfounded.