Kindly follow the link also.
http://www.mpbio.com/product_info.php?products_id=15884Importantly keep in mind phototoxicity of HEPES when exposed to ambient light due to the production of hydrogen peroxide. So its strongly advised to keep any HEPES containing solution in dark.
see theses refs :
* Toxicity of light-exposed Hepes
media. Lepe-Zuniga JL, Zigler JS Jr, Gery I. Journal of Immunological Methods. 1987 Oct 23;103(1):145.
* Analysis of the cytotoxic effects of light-exposed HEPES-containing culture medium.
* Zigler JS Jr, Lepe-Zuniga JL, Vistica B, Gery I., In Vitro Cell Dev Biol. 1985 May;21(5):282-7.