3/24/21

Dear Tejaswini,

Your e-mail doesn't provide enough information to formulate an accurate answer. Is your medium something that you formulated yourself, or is it a commercial, pre-sterilized formulation? Media for animal (e.g., epithelial) cells can be tricky to prepare as they often contain many ingredients that are temperature and/or pH sensitive.

If you are preparing the medium yourself from dry ingredients, you can make it up in phosphate buffer (instead of DI-water) at a pH between 6 & 7. A PO4 molarity of 25-50 mM should be appropriate. This should work, assuming the cells are not sensitive to PO4 and that PO4 won't cause precipitation of any of the medium ingredients. I would adjust the medium pH after all the ingredients have been dissolved in the buffer, as the ingredients may alter the pH. Adjustment can be made w/ NaOH (or KOH) and H3PO4. If the medium contains heat-sensitive ingredients, it will require filter sterilization, followed by transfer to sterile culture vessels.

If you are working w/ a commercial pre-made, pre-sterilized medium and want to adjust the pH, aseptically remove a small volume of the medium (10-20 mL; Be sure to accurately measure the exact volume.) and carefully titrate it on a pH meter to the desired pH with either acid or base (NaOH or H3PO4). Keep tract of the volume of titrant. After that, knowing the volume of medium in your culture vessels, you can calculate the volume of titrant to add (aseptically) to the medium. Make sure to sterilize the titrant(s).

I hope this information helps you.

Bill Colonna Ames, Iowa, USA [email protected]