We'been preparing B5 media for plant cell culture (MS + Gamborg vit+ 3% sucrose) with and without agar, adjusting with KOH to pH 5.7. We noticed that the pH changes after autoclaving, around 0.7 units, so we have to readjust..
Has anyone had this problem? any suggestions? Thanks
The (NH4)2SO4 is probably the cause. When autoclaving the ammonia is driven off and would change the pH. You are also destroying most of your vitamins by autoclaving. Autoclaving will also cause the magnesium phosphate to precipitate out. Best to autoclave the inert parts of the formulation and filter sterilize the volatile/labile compounds. You then combine under a laminar flow hood (magnesium stock included) to make the final formulation. If using agar make sure it has cooled to
Haven't specifically checked this or used B5 but for our normal MS medium recipe we use MES as buffer, maybe this could help?
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