What Is HEPES Buffer? Its Role in Cell Culture

HEPES is a buffer added to cell culture media to keep the pH stable, especially when cells spend time outside a CO2 incubator. It is a “good” biological buffer that resists pH swings across the range cells care about. This guide explains what HEPES is, how it works, how to use it, and what to watch for.

What is HEPES?

HEPES is a synthetic zwitterionic buffer that holds pH steady in the physiological range, roughly pH 7.2 to 7.4. Unlike the bicarbonate buffer in most media, HEPES does not depend on a CO2 atmosphere, so it keeps media from drifting toward alkaline pH when cultures are handled on the bench.

Why use HEPES in cell culture?

Most media use a sodium bicarbonate buffer, which only holds the correct pH inside a CO2 incubator. As soon as you take cells out, CO2 escapes and the pH rises. Adding HEPES gives an extra layer of buffering that keeps pH stable during longer manipulations, such as imaging, cell counting, or lengthy setup steps. It is usually used together with the standard bicarbonate buffer rather than replacing it.

How to use HEPES

HEPES is typically added to media at a final concentration of about 10 to 25 mM, either as a component of the medium or from a concentrated stock solution. Use the lowest concentration that keeps pH stable for your workflow. Because HEPES does not replace nutrients or the bicarbonate system, cultures are still usually kept in a CO2 incubator for growth.

What to watch for

HEPES is generally well tolerated, but a few points are worth knowing. At higher concentrations it can be toxic to some sensitive cells, and HEPES-containing media exposed to light can generate reactive species that may harm cells, so protect it from strong light. Use only as much as your workflow needs.