Can I autoclave media to sterilise after having adjusted the pH (5, 6, 7, 8, 9)? Carrying out experiment involving growth under different pH ranges, but must be sterile and don't have access to appropriate filters.
If your media is already sterile, you can add a sterile buffer, such as HEPES to your medium. Agree with other answers provided that you can not autoclave culture media if for mammalian cell cultures. Several components in the media are heat labile and will become inactivated following autoclaving.
Hi Nicolas,
is this for ordinary bacterial media, or something more finicky? Working with LB and related media, we found that pH adjustment followed by autoclaving left the pH unchanged providing the autoclave was well calibrated, the media well mixed and the programme appropriate for the media and didn't cause caramelisation.
If (judging by your topics) this is for mammalian cell culture, the answer is that we never autoclave the medium : it is always prepared, pH adjusted and this is followed by ultrafiltration. Additives that need to be kept as concentrates are dissolved and then filter-sterilised (syringe / 50ml filter tubes) before storage. I appreciate that you don't have filters available, but don't have a better response in this instance.
Best of luck.
Dear Nicolas,
The vast majority of tissue culture media is ONLY able to be sterilized by filtration. However, tissue culture media formulations that are autoclavable are available, and the company will make a point of saying that it is an autoclavable formulation. While they are specially formulated to withstand the autoclave, you must still make up any evaporation that occurs during autoclaving by adding sterile water. For your experiment, you would probably have to change the pH by adding sterile acid or base after you autoclave it, since I am not sure that the formulations are stable for autoclaving at non-physiological pH (ask the company).
It would probably be much cheaper to buy filters, rather than buy new autoclavable media to mix and sterilize. I would also like to point out that, depending on the buffering system in the media, you will still get a slight pH shift during filtration. Since you are looking at points that are one pH unit apart, it probably won't be that important for this experiment.
Good Luck!
Jill
If your media is already sterile, you can add a sterile buffer, such as HEPES to your medium. Agree with other answers provided that you can not autoclave culture media if for mammalian cell cultures. Several components in the media are heat labile and will become inactivated following autoclaving.
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